Institutional Repository | Satya Wacana Christian University: Sistem Otomatisasi Pengatur pH Pada Air Penampungan Kolam Renang

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" ! !

(400 Volts Peak)

The MOC3020 Series consists of gallium arsenide infrared emitting diodes, optically coupled to a silicon bilateral switch.

• To order devices that are tested and marked per VDE 0884 requirements, the suffix ”V” must be included at end of part number. VDE 0884 is a test option. They are designed for applications requiring isolated triac triggering.

Recommended for 115/240 Vac(rms) Applications:

• Solenoid/Valve Controls • Static ac Power Switch

• Lamp Ballasts • Solid State Relays

• Interfacing Microprocessors to 115 Vac Peripherals • Incandescent Lamp Dimmers

• Motor Controls

MAXIMUM RATINGS _{(TA = 25}°C unless otherwise noted)

Rating Symbol Value Unit

INFRARED EMITTING DIODE

Reverse Voltage _VR 3 Volts

Forward Current — Continuous _IF 60 mA

Total Power Dissipation @ TA = 25°C Negligible Power in Triac Driver Derate above 25°C

PD 100

1.33

mW mW/°C OUTPUT DRIVER

Off–State Output Terminal Voltage _VDRM 400 Volts

Peak Repetitive Surge Current (PW = 1 ms, 120 pps)

ITSM 1 A

Total Power Dissipation @ TA = 25°C Derate above 25°C

PD 300

mW mW/°C TOTAL DEVICE

Isolation Surge Voltage(1)

(Peak ac Voltage, 60 Hz, 1 Second Duration)

VISO 7500 Vac(pk)

Total Power Dissipation @ TA = 25°C Derate above 25°C

PD 330

4.4

mW mW/°C

Junction Temperature Range _TJ – 40 to +100 °C

Ambient Operating Temperature Range(2) _TA – 40 to +85 °C

Storage Temperature Range(2) _Tstg – 40 to +150 °C

Soldering Temperature (10 s) _TL 260 °C

1. Isolation surge voltage, VISO, is an internal device dielectric breakdown rating. 1. For this test, Pins 1 and 2 are common, and Pins 4, 5 and 6 are common.

2. Refer to Quality and Reliability Section in Opto Data Book for information on test conditions.

Preferred devices are Motorola recommended choices for future use and best overall value.

GlobalOptoisolator is a trademark of Motorola, Inc.

Order this document by MOC3020/D

SEMICONDUCTOR TECHNICAL DATA

GlobalOptoisolator

*Motorola Preferred Device

SCHEMATIC

[IFT = 15 mA Max]

STANDARD THRU HOLE CASE 730A–04

[IFT = 10 mA Max]

[IFT = 5 mA Max]

1. ANODE 2. CATHODE 3. NC

4. MAIN TERMINAL 5. SUBSTRATE 5.DO NOT CONNECT 6. MAIN TERMINAL

1 2 3 6 5 4 6 1 STYLE 6 PLASTIC

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ELECTRICAL CHARACTERISTICS _{(TA = 25}°C unless otherwise noted)

Characteristic Symbol Min Typ Max Unit

INPUT LED

Reverse Leakage Current (VR = 3 V)

IR — 0.05 100 µA

Forward Voltage (IF = 10 mA)

VF — 1.15 1.5 Volts

OUTPUT DETECTOR (IF = 0 unless otherwise noted) Peak Blocking Current, Either Direction

(Rated VDRM(1))

IDRM — 10 100 nA

Peak On–State Voltage, Either Direction (ITM = 100 mA Peak)

VTM — 1.8 3 Volts

Critical Rate of Rise of Off–State Voltage (Figure 7, Note 2) dv/dt — 10 — V/µs COUPLED

LED Trigger Current, Current Required to Latch Output

(Main Terminal Voltage = 3 V(3)) MOC3021 MOC3022 MOC3023 IFT — — — 8 — — 15 10 5 mA

Holding Current, Either Direction _IH — 100 — µA

1. Test voltage must be applied within dv/dt rating.

2. This is static dv/dt. See Figure 7 for test circuit. Commutating dv/dt is a function of the load–driving thyristor(s) only.

3. All devices are guaranteed to trigger at an IF value less than or equal to max IFT. Therefore, recommended operating IF lies between max 3. _{IFT (15 mA for MOC3021, 10 mA for MOC3022, 5 mA for MOC3023) and absolute max IF (60 mA).}

–800

TYPICAL ELECTRICAL CHARACTERISTICS

TA = 25°C

Figure 1. LED Forward Voltage versus Forward Current

2 1.8 1.6 1.4 1.2 1

1 10 100 1000

IF, LED FORWARD CURRENT (mA)

VF , FOR W ARD VOL TAGE (VOL TS)

85°C 25°C

Figure 2. On–State Characteristics

–3

VTM, ON–STATE VOLTAGE (VOLTS)

–400 0 +400 +800

–2 –1 0 1 2 3

, ON-ST

TE CURRENT

(mA)

TA = –40°C PULSE ONLY PULSE OR DC

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TA, AMBIENT TEMPERATURE (°C) – 40

100

– 30 – 20 –10 0 10 20 30 40 50 60 70 80 10

I DRM

, LEAKAGE CURRENT

(nA)

0.7

Figure 3. Trigger Current versus Temperature

–40

TA, AMBIENT TEMPERATURE (°C) 0.8

1.1 1.3 1.4

–20 0 20 40 60 80

FTI

0.6

100

PWin, LED TRIGGER WIDTH (µs) 10

15 20 25

2 5 10 20 50

100

FTI

, NORMALIZED LED

TRIGGER CURRENT

NORMALIZED TO: PWin q 100 µs

Figure 4. LED Current Required to Trigger versus LED Pulse Width

TA, AMBIENT TEMPERATURE (°C) 4

6 8 10

25 30 50 60 70 80

100 90 12

STATIC dv/dt CIRCUIT IN FIGURE 7

Figure 5. dv/dt versus Temperature

+400 Vdc PULSE INPUT MERCURY WETTED RELAY RTEST CTEST

R = 10 kΩ

X100 SCOPE PROBE D.U.T.

APPLIED VOLTAGE

WAVEFORM 252 V

0 VOLTS

tRC

Vmax = 400 V

dvńdt +0.63 Vmax_t

RC +

252 t_RC

1. The mercury wetted relay provides a high speed repeated pulse to the D.U.T.

2. 100x scope probes are used, to allow high speeds and voltages.

3. The worst–case condition for static dv/dt is established by triggering the D.U.T. with a normal LED input current, then removing the current. The variable RTEST allows the dv/dt to be gradually increased until the D.U.T. continues to trigger in response to the applied voltage pulse, even after the LED current has been removed. The dv/dt is then decreased until the D.U.T. stops triggering. _t_{RC is measured at this point and} recorded.

, TRIGGER CURRENT

– NORMALIZED 0.9 1 1.2 µ dv/dt, ST A TIC (V/ s)

Figure 6. Leakage Current, IDRM versus Temperature

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Rin 1 2

4 360 MOC

3021/ 3022/ 3023

470

0.05 µF

Figure 8. Typical Application Circuit

0.01 µF 39

HOT 240 VAC

GROUND LOAD

VCC

* This optoisolator should not be used to drive a load directly. It is in-tended to be a trigger device only.

In this circuit the “hot” side of the line is switched and the load connected to the cold or ground side.

The 39 ohm resistor and 0.01 µF capacitor are for snub-bing of the triac, and the 470 ohm resistor and 0.05 µF ca-pacitor are for snubbing the coupler. These components may or may not be necessary depending upon the particu-lar triac and load used.

Additional information on the use of optically coupled triac drivers is available in Application Note AN–780A.

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PACKAGE DIMENSIONS

CASE 730A–04 ISSUE G

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH. 3. DIMENSION L TO CENTER OF LEAD WHEN

FORMED PARALLEL. 6 4 1 3 –A– –B– SEATING PLANE –T– 4 PL F K C N G 6 PL D 6 PL E M A M

0.13 (0.005) T B M L M 6 PL J M B M

0.13 (0.005) T A M

DIM MIN MAX MIN MAX MILLIMETERS INCHES

A 0.320 0.350 8.13 8.89 B 0.240 0.260 6.10 6.60 C 0.115 0.200 2.93 5.08 D 0.016 0.020 0.41 0.50 E 0.040 0.070 1.02 1.77 F 0.010 0.014 0.25 0.36 G 0.100 BSC 2.54 BSC J 0.008 0.012 0.21 0.30 K 0.100 0.150 2.54 3.81 L 0.300 BSC 7.62 BSC M 0 15 0 15 N 0.015_ 0.100_ 0.38_ 2.54_

STYLE 6: PIN 1. ANODE

2. CATHODE 3. NC 4. MAIN TERMINAL 5. SUBSTRATE 6. MAIN TERMINAL

CASE 730C–04 ISSUE D –A– –B– _S SEATING PLANE –T– J K L 6 PL M B M

0.13 (0.005) _T A M C

D6 PL

M A M

0.13 (0.005) T B M H

G E6 PL

F4 PL

3 1

4 6

NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH.

DIM MIN MAX MIN MAX MILLIMETERS INCHES

A 0.320 0.350 8.13 8.89 B 0.240 0.260 6.10 6.60 C 0.115 0.200 2.93 5.08 D 0.016 0.020 0.41 0.50 E 0.040 0.070 1.02 1.77 F 0.010 0.014 0.25 0.36 G 0.100 BSC 2.54 BSC H 0.020 0.025 0.51 0.63 J 0.008 0.012 0.20 0.30 K 0.006 0.035 0.16 0.88 L 0.320 BSC 8.13 BSC S 0.332 0.390 8.43 9.90

*Consult factory for leadform option availability

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6 Motorola Optoelectronics Device Data

*Consult factory for leadform option availability NOTES:

1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982.

2. CONTROLLING DIMENSION: INCH. 3. DIMENSION L TO CENTER OF LEAD WHEN

FORMED PARALLEL. CASE 730D–05 ISSUE D 6 4 1 3 –A– –B– N C K G F4 PL

SEATING

D6 PL E6 PL

PLANE –T–

M A M

0.13 (0.005) _T B M L

DIM MIN MAX MIN MAX MILLIMETERS INCHES

Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. “Typical” parameters can and do vary in different applications. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury or death may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer.

How to reach us:

USA / EUROPE: Motorola Literature Distribution; JAPAN: Nippon Motorola Ltd.; Tatsumi–SPD–JLDC, Toshikatsu Otsuki,

P.O. Box 20912; Phoenix, Arizona 85036. 1–800–441–2447 6F Seibu–Butsuryu–Center, 3–14–2 Tatsumi Koto–Ku, Tokyo 135, Japan. 03–3521–8315 MFAX: RMFAX0@email.sps.mot.com – TOUCHTONE (602) 244–6609 HONG KONG: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park, INTERNET: http://Design–NET.com 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852–26629298

MOC3020/D

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This datasheet has been download from:

www.datasheetcatalog.com

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pH

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Preface

The importance of pH

Many of nature's processes are highly dependent on pH. This is also the case for the chemical reactions which take place in industry or in a labo-ratory. In 1909, the founder of the modern pH concept, S.P.L. Sørensen, proved that pH is essential for many enzymatic processes. One example is the cleavage of cane sugar using invertase.

pH can also have an influence on the colour of certain dyestuffs. For ex-ample, although cyanidin chloride gives the cornflower its blue hue, it is the same dyestuff which gives a rose its red colour. The explanation is that cyanidin chloride is blue at a high pH while it is red at a low pH. It is essential as regards living organisms that the pH of the biological fluids is maintained within a narrow pH range.

Swimming pool water is disinfected using a chlorine compound. The chlo-rine's optimal effectiveness and the avoidance of eye irritation can only be assured at a specific pH level.

In galvanic baths, quality and current efficiency is critically dependent on the correct pH. When the residual metals in the rinse water from such baths are precipitated, pH also plays a very important role.

These few though wide-ranging examples illustrate the importance of pH. It is appropriate to mention at this point that it is the pH value which is of significance and therefore not the total concentration of acid or alkaline species.

The booklet

The subject of this booklet is the potentiometric measurement of pH. This is the way in which pH is defined and is the optimal method for ob-taining precise results. Reliable and accurate measurements depend on a number of factors: the quality of the equipment used, the electrode type, the accuracy of the calibration, the maintenance level, good labora-tory practice and so forth.

The scope of this booklet is to discuss these various factors and their importance. Hints and recommendations are given and short theoretical

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Definition of pH ... 4

pH measurements ... 5

Electrode types ... 10

Choosing the right electrode ... 13

Electrode maintenance ... 15

The pH meter ... 19

Buffers ... 21

Calibration ... 23

Temperature influence ... 24

Measuring precautions ... 26

Checking the meter ... 27

Appendix ... 28

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Definition of pH

pH is an abbreviation of “pondus hydrogenii” and was proposed by the Danish scientist S.P.L. Sørensen in 1909 in order to express the very small concentrations of hydrogen ions.

In 1909, pH was defined as the negative base 10 logarithm of the hydro-gen ion concentration. However, as most chemical and biological reac-tions are governed by the hydrogen ion activity, the definition was quickly changed. As a matter of fact, the first potentiometric methods used actually resulted in measurements of ion activity.

The definition based on hydrogen ion activity is the definition we use to-day:

pH = - log₁₀a_H+

This definition is closely related to the operational pH definition which is currently defined using a standardised hydrogen electrode setup and buffers standardised in accordance with IUPAC recommendations.

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pH measurements

The electrode chain

pH is measured using a setup with two electrodes: the indicator elec-trode and the reference elecelec-trode. These two elecelec-trodes are often com-bined into one - a comcom-bined electrode.

When the two electrodes are immersed in a solution, a small galvanic cell is established. The potential developed is dependent on both elec-trodes.

Ideal measuring conditions exist when only the potential of the indicator electrode changes in response to varying pH, while the potential of the reference electrode remains constant.

The measured voltage can be expressed by the Nernst equation in the following way:

E = E_ind - E_ref= E'_T - R • T/F • ln a_H+

where

E = Measured voltage (mV)

E_ind = Voltage of indicator electrode (mV) E_ref = Voltage of reference electrode (mV) E'_T = Temperature dependent constant (mV) R = Gas Constant (8.3144 J/K)

T = Absolute Temperature (K) F = Faraday's constant (96485 C)

By using the base ten logarithm, the formula can be written as: E = E'_T - 2.303 • R • T/F • log a_H+

By introducing the pH definition as pH = -loga_H+, pH can be expressed at the temperature T as follows:

pH_T = pH_T° - E R' • S • T

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where

R' = constant = 0.1984 mV/K

S = sensitivity, a correction factor which takes into account that the electrode response may differ from the theoretical value.

pH° = zero pH which is defined as the pH value at which the measured potential is zero. Figure 2 illustrates that the pH° will change with temperature and that another slope will be observed.

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Electrode construction

The construction of glass indicator electrodes and reference electrodes can be made in various ways. A typical glass electrode and a typical calomel reference electrode are shown below.

Fig. 3. Typical electrode constructions

Salt-bridge solution

'Red Rod' Reference element

Crystals Filling hole

Porous pin Shield

Red Rod inner electrode encap-sulated by red glass tube Inner buffer solution

saturated with KCl

pH sensitive glass bulb

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Both the composition of the glass electrode's pH-sensitive glassand the composition of the glass electrode's inner solution have an influence on the potential which will develop.

The response of the electrode is the voltage developed between the in-side and outin-side of the membrane. This voltage is proportional to the dif-ference in pH in the inner solution and in the sample. The response is caused by an exchange at both surfaces of the swollen membrane be-tween the ions of the glass and the H+_{ions of the solution - an ion}

ex-change which is controlled by the concentration of H+_{in both solutions.}

As the structure of the glass membrane may not be uniform, an asym-metry potential may develop even if pH is the same on both sides. The reference electrode shown on the previous page is a saturated sil-ver/silver chloride electrode (Ag/AgCl) where the two components and the KCl are encapsulated in a red tube. The red tubing affords protection from the harmful effects of light. Contact with the chamber is made by means of a platinum wire and the Ag/AgCl is surrounded by a saturated solution of KCl. The liquid junction, i.e. contact to the measuring solu-tion, is achieved through a porous ceramic pin. The potential which oc-curs is determined by the solubility product of the silver chloride and the concentration of the KCl solution and is therefore constant.

A similar electrode construction can be made using mercury and mercurous chloride (calomel) instead. Such electrodes are not suitable for varying temperatures or temperatures above 60°C.

The potential of the reference electrode should be independent of the sample solution. This ideal situation will occur if all transport in the po-rous pin only involves the K+ and Cl- ions, and if they move at the same speed. This is the case in most samples in the pH range 1 to 13 and when a saturated or 3 M KCl salt-bridge solution is used. Deviation from this optimal situation creates the so-called liquid junction potential. Red Rod electrodes should always used saturated KCl.

Table 1 lists the liquid junction potentials in different samples obtained with saturated KCl as the salt-bridge solution. The liquid junction poten-tial's dependence on sample composition and especially on pH is obvi-ous.

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Table 1. Liquid junction potentials in different samples The table below shows the equivalent conductivity in infinitely diluted so-lutions (λ) of the ions commonly used in salt-bridge solutions. Equal con-ductivity of the cation and anion, used as a measure of their mobility, re-sults in the lowest liquid junction potentials.

Cation λλλλλ Anion λλλλλ

Li+ 38.7 CH₃COO- 40.9

Na+ 50.1 ClO₄- 67.4

K+ _73.5 _NO

- _71.5

NH₄+ 73.6 Cl- 76.4

Br- 78.1

1_/

2 SO₄- - 80.0

H+ _349.8 _OH- _198.3

Table 2. Equivalent conductivity of ions in infinite dilutions (S • cm2_{/equivalent) at 25°C}

Sample Liquid Junction Potential

1M HCl 14.1 mV 0.1M HCl 4.6 mV 0.01M HCl 3.0 mV 0.1M KCl 1.8 mV pH 1.68 buffer 3.3 mV pH 4.01 buffer 2.6 mV pH 4.65 buffer 3.1 mV pH 7.00 buffer 1.9 mV pH 10.01 buffer 1.8 mV 0.01M NaOH 2.3 mV 0.1M NaOH -0.4 mV

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Electrode types

Fig. 4. Different glass electrodes for different applications Glass electrodes

The types shown in Figure 4 are examples of glass electrodes. However, glass electrodes are available in a number of different shapes and lengths to fit a wide range of applications. There are very thin electrodes, spear types, electrodes with a flat membrane for surface measurements and so forth. The shape, size and type of the inner electrode can vary, as can the glass composition of the membrane. The composition of the pH-sensitive glass will, to a large extent, determine the electrode's re-sponse time and its sensitivity to ions other than H+. Sodium and lithium ions and, to a lesser extent, potassium ions, may interfere at high pH values (> pH 11). This is normally called the salt or alkaline error. If there is an abundance of sodium ions and few hydrogen ions, they may penetrate into the swollen glass surface layer. This means that the elec-trode will sense a higher ion concentration and therefore a pH value which is too low will be obtained by the pH meter.

Two disadvantages of glass electrodes are that measuring solutions can damage the glass membrane and that the glass membrane is easily bro-ken. Alternatives to the glass electrode are available but are seldom used as they have other drawbacks, e.g. a long response time. The

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anti-Reference electrodes

A number of different reference electrodes are available. These varia-tions relate to:

• the physical construction of the liquid junction • the composition of the salt-bridge solution • the electrode's electrochemical composition

The most common type of liquid junction is formed by a porous pin. However, depending on the application, other types can be used: circular ceramic junctions, sleeve junctions or an open junction through a thin glass tube. These will ensure a higher outflow of salt-bridge solution which is beneficial when measuring in solutions of very high or very low ionic strength. Certain buffers and samples, for example, tris buffer and slurry also require these types of liquid junctions.

Four different liquid junctions are shown in Fig. 5. The typical outflow of KCl salt-bridge solution for each type is also stated.

Fig. 5. Liquid junction constructions with typical KCl outflow

< 10 µl/h Fibre Porous pin Double junction Annular Reversed sleeve

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KCl should not be used as the salt-bridge solution if: • it will interfere with the measuring solution

• if there is a risk that the liquid junction will become blocked due to precipitation

• if it is immiscible with the sample.

Two alternatives are available: a double junction system, i.e. with a sec-ond salt-bridge which does not contain KCl, or a modified electrode sys-tem can be used. A syssys-tem with mercurous sulfate and potassium sulfate is one example. An overview of some of the combinations is pro-vided in Table 3.

Type of Salt- Potential vs. Potential vs. reference bridge standard H₂ sat. calomel electrode solution(s) electrode electrode Hg/Hg₂Cl₂ sat. KCl 244 mV 0 mV

Ag/AgCl sat. KCl 200 mV - 44 mV

Hg/Hg₂SO₄ sat. K₂SO₄ 640 mV 408 mV Calomel sat. LiCl ~ 200 mV ~ - 45 mV Hg/Hg₂Cl₂ sat. KCl/KNO₃ 244 mV ~ 0 mV Table 3. Potentials for different reference electrodes Combined electrodes

Since it is easier to handle one electrode instead of two, combined elec-trodes (single stem) are very popular. The indicating glass electrode and the reference electrode are simply built into a single physical entity. This helps to ensure that the two electrodes have the same temperature dur-ing operation.

Combined electrodes with symmetrical electrode chains are the optimal construction for obtaining temperature equality in the two electrodes. In these electrodes the inner electrode of the glass electrode is the same type (Ag/AgCl) and has the same dimensions as the reference electrode, and the inner solutions are as identical as possible (saturated with KCl).

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Choosing the right electrode

Choosing the right physical dimensions is straightforward as the sample size and sample vessel will dictate the type you should use. If the elec-trodes are to be used under harsh conditions, types with a plastic stem and protection cap will be suitable. Measurements which are to be per-formed directly on a surface require a flat electrode and so forth.

Fig. 6. Selection of the correct reference electrode for different measuring conditions

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Measurements at high temperatures restrict your choice of electrodes as only certain electrochemical systems can withstand higher temperatures. Calomel electrodes, for example, cannot withstand temperatures above 60°C. However, certain Ag/AgCl reference electrodes can be used in-stead. The temperature range used may also be restricted depending on what the electrode is made of. Low temperature prolongs the response time of the electrodes. Long response times are often caused by branes with high electric resistance which occurs in small or thick mem-branes and in glass compositions which are alkali-resistant.

High pH and high salt concentrations call for electrodes with alkali-resist-ant glass membranes. In all other cases, an electrode with a standard glass composition should be used.

When measuring in emulsions or fatty solutions, it is important to select the correct type of liquid junction. It is also important that the junction is easy to renew and clean. Open liquid junctions or sleeve junctions can therefore be recommended. These types can in some cases also be used for measurements in non-aqueous solutions. However, a salt-bridge solution containing lithium chloride is often preferable. LiCl is soluble in many organic media whereas KCl has a very limited solubility.

If there is a risk that chloride will interfere/contaminate, a reference elec-trode with a chloride-free reference system must be used (e.g. Hg/ Hg₂SO₄ with K₂SO₄ salt-bridge), or a reference electrode with a double salt-bridge construction.

Measuring pH in pure water and other solutions with low ionic strength can pose problems. Although contamination of the measuring solution must be avoided, a fairly high outflow of KCl is necessary to minimise the liquid junction potential. Junctions with annular rings are therefore recommended. Sleeve junctions can also be used although their junction potential is less stable.

High ionic strength solutions and certain buffers also require a high out-flow to ensure that the ionic transport in the junction is still dominated by the KCl ions. Open liquid junctions and sleeve junctions are recom-mended (see figure 5). High precision measurements can sometimes be facilitated by using open liquid junctions with a controlled and small out-flow.

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Electrode maintenance

Proper electrode maintenance ensures: • a faster response

• more reliable measurements • a longer lifetime.

The glass electrode and the reference electrode have different mainte-nance requirements and will therefore be described separately. The infor-mation concerning glass and reference electrodes also applies to com-bined electrodes.

The GK ANNEX Electrode Maintenance Kit from Radiometer Analytical contains all the items necessary for maintaining glass electrodes plus combined and reference electrodes with saturated KCl as the salt-bridge solution.

Glass electrode

The glass membrane must always be clean. For measurements in aque-ous solutions, rinsing with distilled water will often suffice. Rinsing the electrode with a mild detergent solution once a week, such as Radio-meter Analytical's RENOVO•N, will be beneficial. Measurements per-formed in solutions containing fat or protein require stronger cleaning agents, e.g. alkaline hypochlorite solution. RENOVO•X has been devel-oped to meet these requirements.

The glass electrode should be stored in distilled water or in a weak acidic buffer between measurements. Prolonged use of strong alkaline solu-tions or even weak solusolu-tions of hydrofluoric acid will severely reduce the lifetime of the electrode as the glass membrane will gradually be dis-solved. This occurs more rapidly at high temperatures.

For overnight storage, combined electrodes should be stored in refilling solution.

If the electrode is not to be used for 2 weeks or more, dry storage is rec-ommended. Remember to soak the electrode well before use.

No air bubbles must be trapped around the inner reference electrode as unstable readings may result. Tap the electrode gently or swing it in

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cir-cles by its cable. If the air bubbles are trapped by KCl crystals, heating the electrode gently to max. 60°C in a water bath may also prove neces-sary.

To establish a stable, swollen, glass layer around the pH-sensitive glass, new or dry-stored glass electrodes have to be soaked in distilled water or an acidic buffer for some hours before use. Normal response times will be achieved after approx. 24 hours, although a longer soaking period may be needed for small electrodes. If measurements are needed before this time, calibrations should be repeated often due to drifting po-tentials.

If the response of a glass electrode has become sluggish, slight etching of the outer glass layer may help. The recommended treatment (which should only be performed when other measures have failed) consists of 1 minute in 20% ammonium bifluoride solution followed by 15 seconds in 6 M hydrochloric acid. Care should be exercised when carrying out this treatment as the risk of the formation of hydrofluoric acid is present. The electrode should then be thoroughly rinsed and soaked for 24 hours in water or in an acidic buffer solution.

In aqueous solutions, the function of the glass electrode depends on the hydration (swelling) of the glass layer which takes place on the surface of the pH-sensitive glass during soaking and measurement. However, measurements in non-aqueous or partly non-aqueous solutions are also possible as long as the electrode is frequently rehydrated, i.e. soaked in water or an acidic buffer. Between measurements in a non-aqueous sol-vent which is immiscible with water and before soaking, the electrode should first be rinsed with a solvent which is miscible with both water and the solvent before finally rinsing with water.

Because of the extremely small currents which pass through the glass electrode, the cable, plug and connector must be kept clean and dry if reliable measurements are to be obtained.

The lifetime of a glass electrode depends on a number of factors and is therefore highly individual. Good maintenance will prolong the lifetime whereas high temperatures, alkaline solutions, repeated etchings and im-proper maintenance will reduce the electrode's lifetime. However, the composition of the glass membrane will gradually deteriorate even during dry storage. As a guide, standard glass electrodes in normal use can last for a year or two.

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Reference electrode

It is also important that the reference electrode is kept clean. As a mat-ter of fact, most electrode problems can

be traced to the reference electrode. It can be rinsed in the same solutions as those used for the glass electrode. The reference electrode must always be nearly filled with salt-bridge solution. Po-tassium chloride in a high concentration is normally used.

Calomel and red rod electrodes from Radi-ometer Analytical require saturated potas-sium chloride solution (KCl•L). This means that KCl crystals should always be present in the salt-bridge solution.

The special reference electrodes for chlo-ride-free solutions or for non-aqueous so-lutions should, of course, be filled with the appropriate solution. This will normally be potassium sulfate and lithium chloride

re-spectively. Reference electrodes with a double salt-bridge contain potas-sium chloride in the inner one and a suitable salt in the outer one (high concentrations of KNO₃, NH₄NO₃ and Li-Acetate are some of the most often used solutions).

If the reference electrode is not capped and stored dry, it should prefer-ably be stored in a beaker containing salt-bridge solution. The ability of concentrated KCl solutions to creep should, however, be kept in mind. The direction of flow in the reference electrode should always be from the electrode to the measuring solution. As this one-way flow can only be partly achieved, the salt-bridge solution should be changed regularly, e.g. once a month.

Liquid junctions with fibres or ceramic pins can occasionally become blocked due to crystallisation (e.g. of KCl). If soaking in KCl solution does not solve the problem, raising the temperature to the maximum al-lowable for the reference system will often help. Other types of blockage can also occur, for example, in the form of a precipitate (black) of silver chloride or mercury sulfide in the porous pin. Gentle use of abrasive pa-per can sometimes remove the precipitate. In other cases, chemical

pro-Saturated KCl

inner reservoir

Second salt-bridge

outer reservoir

Fig. 7. Double junction reference electrode

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cedures such as soaking the electrode for a few hours in an acidic solu-tion of thiourea (1 M thiourea in 0.1 M HCl) can be used.

A malfunction can also be caused by trapped air bubbles. These bubbles can be removed by gently tapping the electrode. If this does not alleviate the problem, the electrode shaft should be dipped in salt-bridge solution and heated to 60°C.

The lifetime of reference electrodes also depends on maintenance and especially on the liquid junction zone not becoming blocked. The elec-trode must never dry out and should therefore always be filled with the proper and uncontaminated, salt-bridge solution. A lifetime of 2 years or more is, in most cases, obtainable.

If the above recommendations have been followed, a proper calibration should be able to be performed easily. If this is not the case, the elec-trodes should be exchanged or examined more closely. The response time of the electrodes can be checked during a calibration.

The pH reading obtained in each of the two buffers should be stable within approx. one minute, otherwise the electrode's condition is poor. It is strongly recommended that the zero pH and sensitivity are noted down after each calibration since a large deviation from one calibration to the next indicates that there is a problem. Radiometer Analytical recom-mends the use of the GLP•LOGBOOK for this purpose. It is part of the GK ANNEX kit.

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The pH meter

A pH meter measures the potential difference (in mV) between the elec-trodes and converts it to a display of pH.

In order to obtain a correct measurement, the input amplifier and the converting circuit must meet certain requirements. The principal con-struction of a pH meter can be seen in the simplified diagram below.

Fig. 8. Simplified pH meter diagram.

The potential difference between the reference electrode and the glass electrode is amplified in the mV amplifier before the A/D converter feeds the signal to the microprocessor for result calculation.

As the glass electrode typically has an inner resistance of the order of 108Ω, the amplifier’s input resistance, R_i, must be considerably higher. A value of 1012 is required. For the same reason it is also important that the amplifier does not send any current through the glass electrode as this will give an error potential and could even disturb the electrode. The so-called terminal or bias current, I_term, should therefore be below 10-12A. When R_i >> R_g, I_term = 10-12_{A and R}

g = 108Ω, the error introduced can be

calculated according to Ohm's Law:

V_error = 10-12A • 108Ω = 10-4V = 0.1 mV

To attain reliable and consistent results, the amplifier and other circuits must have a small temperature coefficient, i.e. the influence of tempera-ture variations must be under control.

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Fig. 9. The PHM240 pH/Ion Meter for high-precision pH measurements Normally, the result is displayed in numeric form although a few pH me-ters with poinme-ters are still available. The term analog or digital pH meme-ters is often used to distinguish between these two forms of display. How-ever, it is also used to differentiate between control convert circuitry in analog or digital form.

In an analog pH meter, the adjustment of zero pH and sensitivity is car-ried out using adjustable resistances (dials) and the amplification factor is under direct manual control. The signal is then sent through an A/D converter. The output is a digital signal for the numeric display. In a dig-ital pH meter, the amplifier works under the same conditions all the time and is directly connected to an A/D converter. The converter's output is then manipulated by digital circuitry (microprocessor-based) and the cal-culated pH is then displayed. Use of a temperature sensor provides both temperature correction and a temperature display. For microprocessor systems, the software will often provide automatic recognition of the calibration buffers and even automatic stability control of the electrode signal. To avoid interference, the following points should be checked: • Proper grounding of all types of pH meters will alleviate a lot of

problems related to noisy electrode signals.

• If the pH meter is part of a larger measuring system, all the instru-ments should be connected to the same point.

• If the wall power outlet does not include a proper ground, a separate grounding lead must be used.

• The electrode cables should not run parallel to power lines as they may pick up noise.

• If the measuring solution is grounded (e.g. through pipes or stirrers), the pH meter circuitry must be isolated from ground and connection to other instruments (e.g. recorders or printers) should be performed with great care (galvanic insulation is required). Otherwise there is a great risk of current being passed through the reference electrode, disturbing the measurement and causing irreparable damage.

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Buffers

A calibration is required to match the pH meter to the electrodes. For this purpose a solution with a precisely known pH has to be used. Such a solution must have a certain insensitivity to being lightly contaminated with acid or alkaline species, i.e. it must have a buffering capacity. This is where the terms buffer solution or buffer originate from.

The chemicals used in buffer solutions must be pure and stable, the pH values should be well-defined and the liquid junction potential should be the same size as the one for the unknown sample solutions. As these requirements partly contradict each other, two kinds of buffer solutions have been developed: the so-called technical buffers with a high buffer capacity and IUPAC/NIST buffers with a lower buffer capacity. The latter ones are, however, directly in accordance with the pH definition thus en-suring better accuracy, and the different buffers in the series have a high degree of consistency.

Fig. 10. IUPAC Series certified standards in thick, plastic bottles placed in tins assure long shelf life

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The problem of varying liquid junction potentials is minimal as regards normal, diluted sample solutions. Radiometer Analytical buffers are therefore based on this concept.

It should be mentioned in this connection that the Radiometer Analytical buffers are defined using the hydrogen electrode measuring setup. Radiometer Analytical buffers are directly traceable to the hydrogen elec-trode measuring setup at one of the few Primary Laboratories (including NIST and Radiometer Medical A/S). For further information, please refer to the References at the end of the booklet).

The buffers used today have evolved over the years. However, it is inter-esting to note that it was actually S.P.L. Sørensen who proposed many of them. R.G. Bates (formerly employed at the National Bureau of Stand-ards) has made research on a number of buffers and it is his work which forms the basis of the current series of IUPAC/NIST buffers. The series consists of 10 buffers which are listed in the Appendix, together with the temperature dependency of the pH values.

The temperature dependency of the buffers can be expressed using the formula: pH = A/T + B + C • T + D •T2, where T is the temperature in Kelvin. The coefficients A, B, C and D are also listed for each buffer. High precision buffers have only a limited stability. It is therefore recom-mended that they are used within a short period of time, depending though on how precise your measurements have to be. A solution in an opened (but, of course, capped) bottle will only last for a limited period of time. It is the alkaline buffers which pose most problems because they absorb carbon dioxide from the atmosphere. Therefore, even buffers in unopened, thin, plastic bottles have a relatively short shelf life. For the best protection and long shelf life, thick, plastic bottles placed in tins are the optimal solution.

Addition of small amounts of germicide is necessary in order to avoid microbiological growth as several of the buffers are excellent culture me-dia. On the other hand, addition of other substances should be avoided as they could disturb the pH value or the stability of the solution. Some colour compounds may cause problems as they have an adverse effect on the liquid junction.

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Calibration

Electrodes cannot be produced with exactly identical characteristics. Zero pH and sensitivity will vary with time and different manufacturers produce electrodes with different nominal values. The calibration matches the pH meter to the current characteristics of the electrodes. The calibration process is generally performed by measuring in two dif-ferent buffer solutions. This enables both pH° (zero pH) and the slope (sensitivity) to be determined.

Fig. 11. Calibration curve

If the last calibration was performed recently or if you are in a hurry, a one-point calibration with measurement in only one buffer solution can be carried out. In this case, only pH° will be determined and the former sen-sitivity will be used.

The sensitivity is usually stated as a percentage of the theoretical value and should be independent of temperature. However, as mentioned be-fore, the slope expressed as mV/pH is directly dependent on tempera-ture. As an alternative to the sensitivity in %, a slope at 25°C is often used (100% = 59 mV/pH).

pH° is generally used to describe the electrode characteristics. However, the potential at pH 0 or pH 7 at 25 °C can also be given.

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The calibration should be performed in a consistent manner, i.e. always with the same stirring and the same stability criteria or waiting time. The two buffers should also have the same temperature and this must be close to the temperature of the unknown samples. The two buffers should bracket the measuring interval, i.e. for sample measurements be-tween pH 4.5 and 6.7, it would be appropriate to use buffers with pH 4.01 and pH 7.00. Still, the same buffers could also be used in the pH 3 - 8 sample range.

The buffer pH values can be entered from a keyboard or by means of ad-justing dials. However, a number of microprocessor-controlled instru-ments allow autocalibration. This means that the instrument itself will se-lect the right buffer value from a preprogrammed list. The temperature dependency will also be taken into account. It is obvious that the buffers used in autocalibration must have significantly different pH values. Using a buffer which is not included in the list, e.g. a pH 6.86 instead of a pH 7.00 buffer, will result in an incorrect calibration.

Temperature influence

Temperature plays an important role as regards sample and buffer pH and an electrode's characteristics. The temperature dependency of the buffers is fully known and is shown on the rear of the buffer bottles from Radiometer Analytical. The pH variation due to temperature is minimal for inorganic acid buffers, whereas it is significant for alkaline buffers and some organic buffers (please see the buffer tables in the Appendix). As regards the electrodes, compensation can be made for the influence of temperature on the slope. On the other hand, no compensation can been made for the pH shifts caused by altered reference potentials or a change of pH in the inner solution in the glass bulb. Finally, almost noth-ing is known about the influence of temperature on a sample's pH. It is therefore essential that the temperature is registered together with the pH value.

To sum up, samples, buffers and electrodes should all have the same temperature. Some compensation can be performed but it is not possible to calculate the pH of a sample measured at one temperature back to the sample pH at another (reference) temperature.

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Plotting the pH versus mV at a number of different temperatures will, for most electrodes, reveal that the lines intersect at almost the same point (see Figure 12). This point is called the iso potential point or iso-pH. If, by electrical circuitry or calculation, the pH° and iso-pH are made to co-incide, compensation is made for the electrode's temperature depend-ence and measurements in a fairly large temperature range will be possi-ble. The errors can be controlled if sample measurement and calibration are performed at two distinct temperatures. If the glass and reference electrode comprise the same electrochemical system like, for example, the Radiometer Analytical pHC2xxx series of electrodes, the tempera-ture range allowed is larger than it would be with an unequal electrode construction.

The iso-pH is usually determined after a normal two-point calibration by making a third calibration. The third buffer should be the same as one of the first two buffers but the calibration temperature must differ by at least 20°C.

When pH°, sensitivity and iso-pH have all been determined, the pH can be calculated using the following formula:

pH_T = pH° • - + pH_iso (1- T_cal/ T)

Fig. 12. Definition of iso-pH.

The intersection points do not coincide for isotherms at great variations in temperature

E R' • S • T Tcal

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Measuring precautions

The obtainment of reliable measurement results depends on: • the use of high quality equipment

• the maintenance of electrodes • a meter in good condition

• proper procedures being followed.

This means that the calibrations should be performed regularly and that the results should be documented. It is of the utmost importance that the same procedure is used for measurements of the same type. For ex-ample, the stirring conditions should be the same during both calibration and sample measurement. Similarly, the electrode signal's stability crite-ria should not vary within the same measuring situation. This is most easily achieved using modern microprocessor pH meters as the elec-trode signal's stability is monitored automatically.

Odd results are sometimes obtained in suspensions and colloids. In fact, three different pH values may be measured. If the solution is stirred thoroughly, one value is obtained. On the other hand, in a sample which has not been stirred and in which the sediment is precipitated, two other values may be measured: one when the electrode(s) is dipped into the layer of sediment, and another if the electrode(s) is only in contact with the liquid above the sediment.

The electrodes should be held firmly in place and the sample beaker should be in a secure position. Use of an electrode stand specifically constructed to fulfill these requirements is therefore recommended. Temperature should be controlled and, for accurate research measure-ments, a thermostatting bath should be used.

For measurements in solutions with a very low conductivity (these are usually non-aqueous), metal screening of the measuring beaker may be necessary. The alternative, adding a conductive (soluble) salt, is only al-lowed in special cases as the pH may change. These cases also require special reference electrodes which are compatible with the non-aqueous solutions, or which have a large outflow of salt-bridge solution.

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Checking the meter

If problems occur, e.g. during calibration, it is recommended that you check the meter without electrodes in order to separate the two possible problem areas. Electrode simulators exist but are not readily available and are often rather expensive. A less expensive yet still effective check can be made using only simple items and is described below. 1. First of all, check the pH meter in the mV range. Connect the high

impedance input (for the glass electrode) to the low input (for the reference electrode). For Radiometer Analytical pH meters supplied with both a black and red banana bushing, use the black one. 2. The pH meter should now display only a few mV, ideally 0.0 mV.

Now connect a normal 1.5 V dry cell to the same electrode inputs. The meter should, depending on the state of the dry cell, display a reading in the vicinity of 1.5 V.

3. Switch the pH meter to pH mode and connect the high and low impedance inputs to each other again. The red banana bushing must be used for Radiometer Analytical pH meters.

4. Adjust the temperature to 25°C and (if adjustable) the sensitivity to 100% (59 mV/pH). Most meters will now display a value between pH 5.5 and 8.0. If the meter has a buffer adjustment (standardising) dial, turning this dial should alter the display value.

5. Connect the 1.5 V dry cell again. The display should go off range. As 60 mV is approximately 1 pH, the 1.5 V correspond to pH 25.

The above checks indicate that the pH meter is operating correctly and that the display and microprocessor, if any, are working. However, any misalignment and need for internal calibration will not be revealed. The input circuitry of the input amplifier may also be faulty, i.e. low input im-pedance and high terminal current. This can be checked if a high ohmic resistor is available. Perform the check in the following way:

1. Short-circuit the high and low impedance inputs as above (mV range). Note the reading on the display.

2. Now repeat this action but use a resistance of 1GΩ (1000 MΩ). Note the reading on the display. The difference should not be more than approx. 1 mV.

3. Connect the 1.5 V dry cell again and note the reading on the display. 4. Connect the dry cell through the 1 GΩ resistor and note the display

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Appendix

pH values of buffer solutions at different temperatures

The tables below list the coefficients describing the temperature depend-ency for the buffers: pH 1.094, 1.679, 3.557, 3.776, 4.005, 4.650, 6.865, 7.000, 7.413, 7.699, 9.180, 10.012 and 12.454 at 25°C. The pH values at different temperatures are listed on the following pages.

The coefficients A, B, C and D refer to the formula: pH = A/T + B + C • T + D •T2 where T is the temperature in Kelvin.

BUFFER

HCl Saturated Citrate

0.1 M Oxalate Tartrate 0.05 m

pH, 25°C 1.094 1.679 3.557 3.776

A 0 -362.76 -1727.96 1280.40

B 1.0148 6.1765 23.7406 -4.1650 102 • C 0.0062 -1.8710 -7.5947 1.2230

105 • D 0.0678 2.5847 9.2873 0

BUFFER

Phthalate Acetate Phosphate Phosphate

0.1 M

pH, 25°C 4.005 4.650 6.865 7.000

A 0 0 3459.39 1722.78

B 6.6146 7.4245 -21.0574 -3.6787 102 _{• C} _-1.8509 _-1.8746 _7.3301 _1.6436

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BUFFER

Phosphate Tris Borate Carbonate Ca(OH)₂

0.01/0.05

pH, 25°C 7.413 7.699 9.180 10.012 12.454

A 5706.61 3879.39 5259.02 2557.10 7613.65 B -43.9428 -12.9846 -33.1064 -4.2846 -38.5892 102 • C 15.4785 3.5539 11.4826 1.9185 11.9217 105 • D -15.6745 -3.2893 -10.7860 0 -11.2918

Fig. 13. The pH at different temperatures is clearly shown on the buffer bottles from Radiometer Analytical

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BUFFER / pH

Temp. HCl Oxalate Tartrate Citrate

0°C 1.082 1.666 3.863

5°C 1.085 1.668 3.840

10°C 1.087 1.670 3.820

15°C 1.089 1.672 3.803

18°C 1.090 1.674 3.793

19°C 1.091 1.675 3.791

20°C 1.091 1.675 3.788

21°C 1.092 1.676 3.785

22°C 1.092 1.677 3.783

23°C 1.093 1.678 3.780

24°C 1.093 1.678 3.778

25°C 1.094 1.679 3.557 3.776

26°C 1.094 1.680 3.556 3.774

27°C 1.094 1.681 3.555 3.772

28°C 1.095 1.681 3.554 3.770

29°C 1.095 1.682 3.553 3.768

30°C 1.096 1.683 3.552 3.766

35°C 1.098 1.688 3.549 3.759

37°C 1.099 1.690 3.548 3.756

40°C 1.101 1.694 3.547 3.754

45°C 1.103 1.700 3.547 3.750

50°C 1.106 1.707 3.549 3.749

55°C 1.108 1.715 3.554

60°C 1.111 1.723 3.560

65°C 1.113 1.732 3.569

70°C 1.116 1.743 3.580

75°C 1.119 1.754 3.593

80°C 1.121 1.765 3.610

85°C 1.124 1.778 3.628

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BUFFER / pH

Temp. Phthalate Acetate Phosphate Phosphate

0°C 4.000 4.667 6.984 7.118

5°C 3.998 4.660 6.951 7.087

10°C 3.997 4.655 6.923 7.059

15°C 3.998 4.652 6.900 7.036

18°C 3.999 4.651 6.888 7.024

19°C 4.000 4.651 6.884 7.020

20°C 4.001 4.650 6.881 7.016

21°C 4.001 4.650 6.877 7.013

22°C 4.002 4.650 6.874 7.009

23°C 4.003 4.650 6.871 7.006

24°C 4.004 4.650 6.868 7.003

25°C 4.005 4.650 6.865 7.000

26°C 4.006 4.650 6.862 6.997

27°C 4.007 4.651 6.860 6.994

28°C 4.008 4.651 6.857 6.992

29°C 4.009 4.651 6.855 6.989

30°C 4.011 4.652 6.853 6.987

35°C 4.018 4.655 6.844 6.977

37°C 4.022 4.656 6.841 6.974

40°C 4.027 4.659 6.838 6.970

45°C 4.038 4.666 6.834 6.965

50°C 4.050 4.673 6.833 6.964

55°C 4.064 4.683 6.833 6.965

60°C 4.080 4.694 6.836 6.968

65°C 4.097 4.706 6.840 6.974

70°C 4.116 4.720 6.845 6.982

75°C 4.137 4.736 6.852 6.992

80°C 4.159 4.753 6.859 7.004

85°C 4.183 4.772 6.867 7.018

90°C 4.208 4.793 6.876 7.034

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BUFFER / pH

Temp. Phosphate Tris Borate Carbonate Ca(OH)₂

0°C 7.534 8.471 9.464 10.317 13.424

5°C 7.500 8.303 9.395 10.245 13.207

10°C 7.472 8.142 9.332 10.179 13.003

15°C 7.448 7.988 9.276 10.118 12.810

18°C 7.436 7.899 9.245 10.084 12.699

19°C 7.432 7.869 9.235 10.073 12.663

20°C 7.429 7.840 9.225 10.062 12.627

21°C 7.425 7.812 9.216 10.052 12.592

22°C 7.422 7.783 9.207 10.042 12.557

23°C 7.419 7.755 9.197 10.032 12.522

24°C 7.416 7.727 9.189 10.022 12.488

25°C 7.413 7.699 9.180 10.012 12.454

26°C 7.410 7.671 9.171 10.002 12.420

27°C 7.407 7.644 9.163 9.993 12.387

28°C 7.405 7.617 9.155 9.984 12.354

29°C 7.402 7.590 9.147 9.975 12.322

30°C 7.400 7.563 9.139 9.966 12.289

35°C 7.389 7.433 9.102 9.925 12.133

37°C 7.386 7.382 9.088 9.910 12.072

40°C 7.380 7.307 9.068 9.889 11.984

45°C 7.373 7.186 9.038 9.857 11.841

50°C 7.367 7.070 9.010 9.828 11.705

55°C 8.985 11.574

60°C 8.962 11.449

65°C 8.941

70°C 8.921

75°C 8.902

80°C 8.884

85°C 8.867

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The composition of the buffers is as follows: Available from Radiometer Analytical:

Oxalate (pH 1.679): 0.05 m KH₃C₄O₈,, part no. S11M001. Phthalate (pH 4.005): 0.05 m KHC₈H₄O₄,part no. S11M002. Phosphate (pH 6.865): 0.025/0.025 m KH₂PO₄/Na₂HPO₄, part no. S11M003.

Phosphate (pH 7.000): KH₂PO₄/Na₂HPO₄, part no. S11M004. Phosphate (pH 7.413): 0.008695/0.03043 m KH₂PO₄/Na₂HPO₄, part no. S11M005.

Borate (pH 9.180): 0.01 m Na₂B₄O₇, part no. S11M006

Carbonate (10.012): 0.025/0.025 m NaHCO₃/Na₂CO₃, part no. S11M007. Ca(OH)₂(pH 12.45): Saturated (at 25°C) and filtered,part no. S11M008. The second phosphate buffer is Radiometer Analytical's own recipe. The other buffers are specified by IUPAC/NIST and DIN 19266.

Not available from Radiometer Analytical:

Tartrate (pH 3.557): Saturated (at 25°C) KHC₄H₄O₆. Citrate (pH 3.776): 0.05 m KH₂C₆H₅O₇.

Acetate (pH 4.650): 0.1/0.1 M C₂H₄O₂/C₂H₃0₂Na. Tris (pH 7.699): 0.01667/0.05 m Tris/Tris-HCl.

Ca(OH)₂(pH 12.454): Saturated (at 25°C) and filtered.

References

1. S.P.L. Sørensen, Comptes-Rendus des Travaux du Laboratoire de Carlsberg 8me Volume 1re Livraison, Copenhague, 1909.

2. R.G. Bates, Determination of pH, Wiley, New York, 1965. 3. Hans Bjarne Christensen, Arne Salomon and Gert Kokholm,

International pH Scales and Certification of pH, Anal. Chem. vol. 63, no. 18, 885A - 891A ,1991.

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-full line

PH ELECTRODE

Model : PE- 03, PE- 11, PE- 01

ISO-9001, CE, IEC1010

PE- 06HD, PE- 04HD, PE- 03K7, PE- 05T

PE-11 PE-03 PE-01 PE-06HD PE-05T PE-03K7

PE-6HD

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full line

pH ELECTRODE

PH ELECTRODE

* General purpose, laboratory and field usage.

Model : PE-03

* 12.3 mm dia. x 160 mm.

* Epoxy body, 1 - 13 pH.

PH ELECTRODE

* General purpose, laboratory and field usage.

Model : PE-11

* 10 mm dia. x 130 mm.

* Epoxy body.

* 1 - 13 pH. (0 - 14 pH typical)

PH ELECTRODE

* Professional, laboratory and field usage.

* 9.5 mm dia. x 130 mm.

* Epoxy body.

* 0 - 14 pH.

SPEAR TI P

* The " Spear Tip pH electrode " is perfect for those pH

PH ELECTRODE

measurements in applications where sample piercing

is required. Meat, sausage and cheese are ideal

Model : PE-06HD

applications. The electrodefeatures a very durable

PE-04HD

glass measuring spear packaged in a rugged virtually

unbreakable epoxy body.

* Range : 0 to 14 pH ( PE-04HD)

* Range : 1 to 13 pH ( PE-06HD)

pH ELECTRODE + Temp. PROBE

* One kit combine of PH electrode PE-03 and Temp.

( combination kit of pH electrode )

probe TP-07 as a whole unit.

* Easy operation for the pH measurement under

Model : PE-03K7

the ATC ( Automatic Temp. Compensation ).

* Available for PH-208, PH-207, PH-207HA, PH-221

YK-2005WA.

pH electrode build in Temp. thermister inside.

pH electrode build in Temp.

* pH meter when make the temperature compensation,

thermister inside.

* the extra optional Temp. probe is not necessary.

Available for PH-207, PH-208, PH-207HA, PH-221,

Model : PE-05T

YK-2005WA,

General purpose, laboratory & field usage. 1 to 13 pH

* ( typical 0 to 14 pH ).

pH Operation Temp. : 5 to 60

℃

( 41 to 140

℉

).

* Temp. Probe Range : 0 to 60

℃

( 32 to 140

℉

).

* Epoxy Body Material.

* Connector :

* BNC plug for pH, ear phone plug for Temp.

(44)

pH Sensor

(Order Code PH-BTA or PH-DIN

)

Our pH Sensor can be used for any lab or demonstration that can be done with a traditional pH meter. This sensor offers the additional

advantages of automated data collection, graphing, and data analysis. Typical activities using our pH sensor include studies of household acids and bases, acid-base titrations, monitoring pH change during chemical reactions or in an aquarium as a result of photosynthesis, investigations of acid rain and buffering, and investigations of water quality in streams and lakes.

Vernier Software & Technology also publishes the following lab books that offer a wide variety of experiments using the pH Sensor:

• Chemistry with Computers and Chemistry with Calculators

• Water Quality with Computers and Water Quality with Calculators

• Biology with Computers and Biology with Calculators

• Physical Science with Computers and Physical Science with Calculators

• Middle School Science with Computers and Middle School Science with Calculators

• Science with Handhelds

• Advanced Chemistry with Vernier

NOTE: This product is to be used for educational purposes only. It is not appropriate for industrial, medical, research, or commercial applications.

Using the pH Sensor with a Computer

This sensor can be used with a computer and any of the following lab interfaces: Vernier LabPro®_{, Go!}®

Link, Universal Lab Interface, or Serial Box Interface. Here is the general procedure to follow when using the pH Sensor with a computer: 1. Connect the pH Sensor to any of the analog ports on the interface.

2. Start the Logger Pro®_{or Logger Lite}® _{software on the computer.}

3. You are now ready to collect data. Logger Pro_{or Logger Lite will identify the pH}

Sensor and load a calibration.2 Click Collect and begin collecting data. 4. If you are using Logger Pro_{software, an alternative to Step 3 is to open an}

experiment file for the pH Sensor in the Probes & Sensors folder. 5. Measure the pH of some known solutions or pH buffers.

6. For the best accuracy, you may want to calibrate your pH sensor. Follow the

•

If you purchased a PH-DIN, you have received a PH-BTA with a BTA-DIN adapter.

If your system does not support auto-ID, open an experiment file in Logger Pro_{, and you are}

ready to collect data.

calibration instructions on the screen. Additional calibration tips are described in the next section.

Using the pH Sensor with TI Graphing Calculators

This sensor can be used with a TI graphing calculator and any of the following lab interfaces: LabPro, CBL 2™, and Vernier EasyLink®. Here is the general procedure to follow when using the pH Sensor with a graphing calculator:

1. Connect the data-collection interface to the graphing calculator.

2. Connect the pH Sensor to any of the analog ports on the interface or to EasyLink. 3. Start the EasyData® or DataMate App—the application you choose to use

depends on your calculator and interface. See the chart for more information.

4. The pH Sensor will be identified automatically, and you are ready to collect data. If the data-collection application is not on your calculator, use the following

instructions to load it onto the calculator.

• EasyData App–This program may already be installed on your calculator. Check to see that it is EasyData version 2.0 or newer. If it is not installed or is an older version, it can be downloaded to your computer from the Vernier web site, www.vernier.com/easy/easydata.html. It can then be transferred from the computer to the calculator using TI-Connect and a TI unit-to-computer cable or TI-GRAPH LINK cable. See the Vernier web site,

www.vernier.com/calc/software/index.html for more information on the App and Program Transfer Guidebook.

• DataMate program–This program can be transferred directly from LabPro or CBL 2 to the TI graphing calculator. Use the calculator-to-calculator link cable to connect the two devices. Put the calculator into Receive mode, and then press the Transfer button on the interface.

Using the pH Sensor with Palm Powered™ Handhelds

This sensor can be used with a Palm Powered handheld and the LabPro. 1. Connect the Palm Powered handheld, LabPro and the pH sensor. 2. Start DataPro.

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set up a new experiment. The pH Sensor will be identified automatically. 4. You are now ready to collect data.

pH Electrode Specifications

Type: Sealed, gel-filled, epoxy body, Ag/AgCl Response time: 90% of final reading in 1 second Temperature range: 5 to 80°C

12 mm OD Range: pH 0-14

12-bit Resolution (LabPro, ULI II, Serial Box Interface) 0.005 pH units 10-bit Resolution (CBL 2): 0.02 pH units

Isopotential pH: pH 7 (point at which temperature has no effect on output) Output: 59.2 mV/pH at 25°C

How the pH Sensor Works

The pH Amplifier inside the handle is a circuit which allows a standard combination pH electrode (such as the Vernier 7120B) to be monitored by a lab interface. The cable from the pH Amplifier ends in a BTA plug.

The pH Sensor will produce a voltage of 1.75 volts in a pH 7 buffer. The voltage will increase by about 0.25 volts for every pH number decrease. The voltage will decrease by about 0.25 volts/pH number as the pH increases.

The Vernier gel-filled pH Sensor is designed to make measurements in the pH range of 0 to 14. A polycarbonate body that extends below the glass sensing bulb of the electrode makes this probe ideal for the demands of a middle school, high school, or university level science class or for making measurements in the environment. The gel-filled reference half cell is sealed—it never needs to be refilled.

This sensor is equipped with circuitry that supports auto-ID. When used with LabPro, Go! Link, EasyLink, or CBL 2, the data-collection software identifies the sensor and uses pre-defined parameters to configure an experiment appropriate to the recognized sensor.

Preparing for Use

To prepare the electrode to make pH measurements, follow this procedure:

• Remove the storage bottle from the electrode by first unscrewing the lid, then removing the bottle and lid. Thoroughly rinse the lower section of the probe, especially the region of the bulb, using distilled or deionized water.

• When the probe is not being stored in the storage bottle, it can be stored for short periods of time (up to 24 hours) in pH-4 or pH-7 buffer solution. It should never be stored in distilled water.

• Connect the pH Sensor to your lab interface, load or perform a calibration (as described in the next section), and you are ready to make pH measurements.

Note: Do not completely submerge the sensor. The handle is not waterproof.

distilled water. Slide the cap onto the electrode body, then screw the cap onto the storage bottle. Note: When the level of storage solution left in the bottle gets low, you can replenish it with small amounts of tap water the first few times you use the probe (but not indefinitely!). A better solution is to prepare a quantity of pH-4 buffer/KCl storage solution (see the section on Maintenance and Storage) and use it to replace lost solution.

Do I Need to Calibrate the pH Sensor?

We feel that you should not have to perform a new calibration when using the pH Sensor for most experiments in the classroom. We have set the sensor to match our stored calibration before shipping it. You can simply use the appropriate calibration file that is stored in your data-collection program from Vernier in any of these ways: 1. If you ordered the PH-BTA version of the sensor, and you are using it with a

LabPro or CBL 2 interface, then a calibration (in pH) is automatically loaded when the pH Sensor is connected. Note: Each pH Sensor (PH-BTA version) is now calibrated at Vernier. This custom calibration is then stored on the sensor. This means that when you first use it, you will very likely see pH readings that are accurate to +/- 0.02 pH units, without calibration! With time, you may see some minor loss of the initial custom calibration accuracy, but for most purposes (see below), it should not be necessary to calibrate the pH Sensor.

2. If you are using Logger Pro_{software (version 2.0 or newer) on a Macintosh or}

Windows computer, open an experiment file for the pH Sensor, and its stored calibration will be loaded at the same time. Note: If you have an earlier version of Logger Pro_{, a free upgrade is available from our web site.}

3. Any version of the DataMate program (with LabPro or CBL 2) has stored calibrations for this sensor.

4. Any version of Data Pro has stored calibrations for this sensor. Stored Calibration Values for the pH Sensor:

Intercept (k₀): 13.720 Slope (k₁): –3.838

If you are performing a chemistry experiment, or doing water quality testing that requires a very accurate calibration, you can calibrate the Vernier pH Electrode following this procedure:

• Use the 2-point calibration option of the Vernier data-collection program. Rinse the tip of the electrode in distilled water. Place the electrode into one of the buffer solutions (e.g., pH 4). When the voltage reading displayed on the computer or calculator screen stabilizes, enter a pH value, “4”.

• For the next calibration point, rinse the electrode and place it into a second buffer solution (e.g., pH 7). When the displayed voltage stabilizes, enter a pH value, “7”.

• Rinse the electrode with distilled water and place it in the sample to be measured.

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full line

PH ELECTRODE

Model : PE- 03, PE- 11, PE- 01

ISO-9001, CE, IEC1010

PE- 06HD, PE- 04HD, PE- 03K7, PE- 05T

PE-11 PE-03 PE-01 PE-06HD PE-05T PE-03K7

PE-6HD

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full line

pH ELECTRODE

PH ELECTRODE

* General purpose, laboratory and field usage.

Model : PE-03

* 12.3 mm dia. x 160 mm.

* Epoxy body, 1 - 13 pH.

PH ELECTRODE

* General purpose, laboratory and field usage.

Model : PE-11

* 10 mm dia. x 130 mm.

* Epoxy body.

* 1 - 13 pH. (0 - 14 pH typical)

PH ELECTRODE

* Professional, laboratory and field usage.

* 9.5 mm dia. x 130 mm.

* Epoxy body.

* 0 - 14 pH.

SPEAR TI P

* The " Spear Tip pH electrode " is perfect for those pH

PH ELECTRODE

measurements in applications where sample piercing

is required. Meat, sausage and cheese are ideal

Model : PE-06HD

applications. The electrodefeatures a very durable

PE-04HD

glass measuring spear packaged in a rugged virtually

unbreakable epoxy body.

* Range : 0 to 14 pH ( PE-04HD)

* Range : 1 to 13 pH ( PE-06HD)

pH ELECTRODE + Temp. PROBE

* One kit combine of PH electrode PE-03 and Temp.

( combination kit of pH electrode )

probe TP-07 as a whole unit.

* Easy operation for the pH measurement under

Model : PE-03K7

the ATC ( Automatic Temp. Compensation ).

* Available for PH-208, PH-207, PH-207HA, PH-221

YK-2005WA.

pH electrode build in Temp. thermister inside.

pH electrode build in Temp.

* pH meter when make the temperature compensation,

thermister inside.

* the extra optional Temp. probe is not necessary.

Available for PH-207, PH-208, PH-207HA, PH-221,

Model : PE-05T

YK-2005WA,

General purpose, laboratory & field usage. 1 to 13 pH

* ( typical 0 to 14 pH ).

pH Operation Temp. : 5 to 60

℃

( 41 to 140

℉

).

* Temp. Probe Range : 0 to 60

℃

( 32 to 140

℉

).

* Epoxy Body Material.

* Connector :

* BNC plug for pH, ear phone plug for Temp.

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pH Sensor

(Order Code PH-BTA or PH-DIN

)

Our pH Sensor can be used for any lab or demonstration that can be done with a traditional pH meter. This sensor offers the additional

Vernier Software & Technology also publishes the following lab books that offer a wide variety of experiments using the pH Sensor:

• Chemistry with Computers and Chemistry with Calculators

• Water Quality with Computers and Water Quality with Calculators

• Biology with Computers and Biology with Calculators

• Physical Science with Computers and Physical Science with Calculators

• Middle School Science with Computers and Middle School Science with Calculators

• Science with Handhelds

• Advanced Chemistry with Vernier

NOTE: This product is to be used for educational purposes only. It is not appropriate for industrial, medical, research, or commercial applications.

Using the pH Sensor with a Computer

This sensor can be used with a computer and any of the following lab interfaces: Vernier LabPro®_{, Go!}®

2. Start the Logger Pro®_{or Logger Lite}® _{software on the computer.}

3. You are now ready to collect data. Logger Pro_{or Logger Lite will identify the pH}

Sensor and load a calibration.2 Click Collect and begin collecting data. 4. If you are using Logger Pro_{software, an alternative to Step 3 is to open an}

experiment file for the pH Sensor in the Probes & Sensors folder. 5. Measure the pH of some known solutions or pH buffers.

6. For the best accuracy, you may want to calibrate your pH sensor. Follow the

•

If you purchased a PH-DIN, you have received a PH-BTA with a BTA-DIN adapter.

If your system does not support auto-ID, open an experiment file in Logger Pro_{, and you are}

ready to collect data.

2

calibration instructions on the screen. Additional calibration tips are described in the next section.

Using the pH Sensor with TI Graphing Calculators

1. Connect the data-collection interface to the graphing calculator.

2. Connect the pH Sensor to any of the analog ports on the interface or to EasyLink. 3. Start the EasyData® or DataMate App—the application you choose to use

depends on your calculator and interface. See the chart for more information.

4. The pH Sensor will be identified automatically, and you are ready to collect data. If the data-collection application is not on your calculator, use the following

instructions to load it onto the calculator.

www.vernier.com/calc/software/index.html for more information on the App and Program Transfer Guidebook.

Using the pH Sensor with Palm Powered™ Handhelds

This sensor can be used with a Palm Powered handheld and the LabPro. 1. Connect the Palm Powered handheld, LabPro and the pH sensor. 2. Start DataPro.

(4)

set up a new experiment. The pH Sensor will be identified automatically. 4. You are now ready to collect data.

pH Electrode Specifications

Type: Sealed, gel-filled, epoxy body, Ag/AgCl Response time: 90% of final reading in 1 second Temperature range: 5 to 80°C

12 mm OD Range: pH 0-14

12-bit Resolution (LabPro, ULI II, Serial Box Interface) 0.005 pH units 10-bit Resolution (CBL 2): 0.02 pH units

Isopotential pH: pH 7 (point at which temperature has no effect on output) Output: 59.2 mV/pH at 25°C

How the pH Sensor Works

Preparing for Use

To prepare the electrode to make pH measurements, follow this procedure:

• Connect the pH Sensor to your lab interface, load or perform a calibration (as described in the next section), and you are ready to make pH measurements.

Note: Do not completely submerge the sensor. The handle is not waterproof. When you are finished making measurements, rinse the tip of the electrode with

Do I Need to Calibrate the pH Sensor?

2. If you are using Logger Pro_{software (version 2.0 or newer) on a Macintosh or}

3. Any version of the DataMate program (with LabPro or CBL 2) has stored calibrations for this sensor.

4. Any version of Data Pro has stored calibrations for this sensor. Stored Calibration Values for the pH Sensor:

Intercept (k₀): 13.720 Slope (k₁): –3.838

If you are performing a chemistry experiment, or doing water quality testing that requires a very accurate calibration, you can calibrate the Vernier pH Electrode following this procedure:

• For the next calibration point, rinse the electrode and place it into a second buffer solution (e.g., pH 7). When the displayed voltage stabilizes, enter a pH value, “7”.

• Rinse the electrode with distilled water and place it in the sample to be measured.

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5

pH Buffer Solutions

In order to do a calibration of the pH Sensor, or to confirm that a saved pH calibration is accurate, you need to have a supply of pH buffer solutions that cover the range of pH values you will be measuring. We recommend buffer solutions of pH 4, 7, and 10.

• Vernier sells a pH buffer kit (order code PHB, $10.00). The kit has 10 tablets: two tablets each of buffer pH 4, 7, and 10. Each tablet is added to 100 mL of distilled or deionized water to prepare respective pH buffer solutions.

• Flinn Scientific (www.flinnsci.com, Tel: 800-452-1261) sells a wide variety of buffer tablets and prepared buffer solutions.

• You can prepare your own buffer solutions using the following recipes:

• pH 4.00

• Add 2.0 mL of 0.1 M HCl to 1000 mL of 0.1 M potassium

hydrogen phthalate.

• pH 7.00

• Add 582 mL of 0.1 M NaOH to 1000 mL of 0.1 M potassium

dihydrogen phosphate.

• pH 10.00

• Add 214 mL of 0.1 M NaOH to 1000 mL of 0.05 M sodium bicarbonate.

Maintenance and Storage

Short-term storage (up to 24 hours): Place the electrode in pH-4 or pH-7 buffer solution.

Long-term storage (more than 24 hours): Store the electrode in a buffer pH-4/KCl storage solution in the storage bottle. The pH Electrode is shipped in this solution. Vernier sells 500 mL bottles of replacement pH Storage Solution (order code PH-SS, $12.00), or you can prepare additional storage solution by adding 10 g of solid potassium chloride (KCl) to 100 mL of buffer pH-4 solution. Flinn Scientific 452-1261) sells a Buffer Solution Preservative (order code B0175) that can be added to this storage solution. By storing the electrode in this solution, the reference portion of the electrode is kept moist. Keeping the reference junction moist adds to electrode longevity and retains electrode response time when the unit is placed back into service. If the electrode is inadvertently stored dry (we don’t recommend this!), immerse the unit in soaking solution for a minimum of eight hours prior to service. When testing a pH Sensor, it is best to place it into a known buffer solution. This allows you to see if the sensor is reading correctly (e.g., in a buffer pH 7, is the sensor reading close to pH 7). Do not place your sensor into distilled water to check for readings—distilled water can have a pH reading anywhere between 5.5 and 7.0, due to variable amounts of carbon dioxide dissolved from the atmosphere.

Furthermore, due to a lack of ions, the pH values reported with the sensor in distilled water will be erratic.

If your pH Sensor is reading slightly off of the known buffer pH (e.g., reads 6.7 in a buffer 7), you may simply need to calibrate the sensor. You can calibrate the sensor

6

in two buffer solutions for two calibration points. If you do not remember or know how to perform a calibration, refer to the booklet that came with the pH sensor. If your readings are off by several pH values, the pH readings do not change when moved from one buffer solution to another different buffer, or the sensor’s response seems slow, the problem may be more serious. Sometimes a method called "shocking" is used to revive pH electrodes. To shock your pH Sensor, perform the following: 1. Let the pH Electrode soak for 4-8 hours in an HCl solution between 0.1 and

1.0 M.

2. Rinse off the electrode and let it sit in some buffer pH 7 for an hour or so. 3. Rinse the electrode and give it another try.

Mold growth in the buffer/KCl storage solution can be prevented by adding a commercial growth inhibitor. This mold will not harm the electrode and can easily be removed using a light detergent solution.

This sensor is designed to be used in aqueous solutions. The polycarbonate body of the sensor can be damaged by many organic solvents. In addition, do not use the sensor in solutions containing: perchlorates, silver ions, sulfide ions, biological samples with high concentrations of proteins, or Tris buffered solutions. Do not use it in hydrofluoric acid or in acid or base solutions with a concentration greater than 1.0 molar. The electrode may be used to measure the pH of sodium hydroxide solutions with a concentration near 1.0 molar, but should not be left in this concentration of sodium hydroxide for periods longer than 5 minutes. Using or storing the electrode at very high temperatures or very low temperatures (near 0°C) can damage it beyond repair.

Warranty

Vernier warrants this product to be free from defects in materials and workmanship for a period of five years from the date of shipment to the customer. This warranty does not cover damage to the product caused by abuse or improper use.

Additionally, the warranty does not cover accidental breakage of the glass bulb of the pH Sensor.

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Vernier Software & Technology 13979 S.W. Millikan Way • Beaverton, OR 97005-2886 Toll Free (888) 837-6437 • (503) 277-2299 • FAX (503) 277-2440

info@vernier.com • www.vernier.com Rev 12/27/06

Logger Pro, Logger Lite, Vernier LabPro, Go!Link, Vernier EasyLink and other marks shown are our registered trademarks in the United States.

CBL 2, TI-GRAPH LINK, and TI Connect are trademarks of Texas Instruments.

All other marks not owned by us that appear herein are the property of their respective owners, who may or may not be affiliated with, connected to, or sponsored by us.

Institutional Repository | Satya Wacana Christian University: Sistem Otomatisasi Pengatur pH Pada Air Penampungan Kolam Renang

" ! !

(400 Volts Peak)

SEMICONDUCTOR TECHNICAL DATA

This datasheet has been download from:

www.datasheetcatalog.com

pH

Preface

Contents

Definition of pH

pH measurements

Electrode types

Choosing the right electrode

Electrode maintenance

The pH meter

Buffers

Calibration

Temperature influence

Measuring precautions

Checking the meter

Appendix

References

-full line

PH ELECTRODE

Model : PE- 03, PE- 11, PE- 01

ISO-9001, CE, IEC1010

PE- 06HD, PE- 04HD, PE- 03K7, PE- 05T

full line

pH ELECTRODE

PH ELECTRODE

* General purpose, laboratory and field usage.

Model : PE-03

* 12.3 mm dia. x 160 mm.

* Epoxy body, 1 - 13 pH.

PH ELECTRODE

* General purpose, laboratory and field usage.

Model : PE-11

* 10 mm dia. x 130 mm.

* Epoxy body.

* 1 - 13 pH. (0 - 14 pH typical)

PH ELECTRODE

* Professional, laboratory and field usage.

* 9.5 mm dia. x 130 mm.

* Epoxy body.

* 0 - 14 pH.

SPEAR TI P

* The " Spear Tip pH electrode " is perfect for those pH

PH ELECTRODE

measurements in applications where sample piercing

is required. Meat, sausage and cheese are ideal

Model : PE-06HD

applications. The electrodefeatures a very durable

PE-04HD

glass measuring spear packaged in a rugged virtually

unbreakable epoxy body.

* Range : 0 to 14 pH ( PE-04HD)

* Range : 1 to 13 pH ( PE-06HD)

pH ELECTRODE + Temp. PROBE

* One kit combine of PH electrode PE-03 and Temp.

( combination kit of pH electrode )

probe TP-07 as a whole unit.

* Easy operation for the pH measurement under

Model : PE-03K7

the ATC ( Automatic Temp. Compensation ).

* Available for PH-208, PH-207, PH-207HA, PH-221

YK-2005WA.

pH electrode build in Temp. thermister inside.

pH electrode build in Temp.

* pH meter when make the temperature compensation,

thermister inside.

* the extra optional Temp. probe is not necessary.

Available for PH-207, PH-208, PH-207HA, PH-221,

Model : PE-05T

YK-2005WA,

General purpose, laboratory & field usage. 1 to 13 pH

* ( typical 0 to 14 pH ).

pH Operation Temp. : 5 to 60

℃

( 41 to 140

℉