Sam ple T itration
Sam ple T itration
1. Fill the sam ple bottle to overflow ing to ensure N ote: T he sam ple can be titrated w ith either a H ach that no air bubbles are trapped in the bottle.
“ D igital T itrator” or a standard burette. R eplace the glass stopper. Invert to check for air bubbles. T his m inim izes the risk of
additional aeration of the sam ple.
6 B.O.D. is a measure of the amount of oxygen consumed in the
biological processes that break down organic matter in water. The greater the BOD, the less oxygen is available for other biological uses (including salmonid respiration).
O ption 1: H ach D igital T itrator M ethod O ption 2: B urette T itration M ethod U se H ach M ethod 8215 as described below , using
1. R em ove the glass stopper and fill a 200 m l 0.2N sodium thiosulfate titrant.
volum etric flask w ith a sam ple. T ransfer this 200 m l portion to a 500-m l E rlenm eyer flask.
1. R em ove the glass stopper and fill a 200 m l volum etric flask w ith a sam ple. T ransfer this
2. Fill a 10 m l burette w ith standard sodium 200 m l portion to a 500-m l E rlenm eyer flask.
thiosulfate titrant (0.025N ). Slow ly add titrant Insert sodium thiosulfate cartridge into the
to the sam ple drop by drop. titrator. 7
3. Sw irl the flask w hile titrating to ensure good
2. Insert a clean delivery tube (approxim ately m ixing. T he sam ple w ill turn a pale yellow 1/16th diam eter “ hook” ) into the titration
color, w hich m eans the endpoint is cartridge (that com es w ith the m onitoring kit).
approaching.
4. A dd 1 m l of Starch Indicator Solution. N ote: A the plunger for the titrator gently until it
A ttach the cartridge to the titrator body. L ow er
d a rk b lu e co lo r w ill d e v e lo p . . contacts the sodium thiosulfate cartridge.
5. C ontinue addition of titrant drop by drop until
3. T urn the delivery knob to eject a few drops of the sam ple changes from dark blue to clear. titrant. R eset the counter to zero and w ipe the
N O T E : Take care not to overrun the end tip of the delivery tube.
p o in t.
4. Place the delivery tube tip into the sam ple.
6. R ead the am ount of titrant used to reach the T urn the delivery knob clockw ise to add titrant
endpoint. 1 m l of titrant = 1 m g/l D O . to the sam ple. N O T E : swirl the flask while
a d d in g titra n t to m a ke su re it m ixes . T he
O xygen Percent Saturation
sam ple w ill gradually turn a pale yellow color.
A tm ospheric pressure varies w ith w eather and
5. O nce the sam ple is pale yellow , the endpoint of elevation. A t sea level, it averages near 760 m m
the titration is approaching. A dd a 1 m l
H g. A s elevation increases, pressure decreases. dropper of Starch Indicator Solution (also a
T he average pressure at B urns (4,200 feet) is 750 part of the kit) and sw irl to m ix. N ote: A dark m m H g. E xtrem es observed in O regon average
b lu e co lo r w ill d e v e lo p . from a low of 632 to a high of 780 m m H g.
6. C ontinue the titration until the sam ple turns from blue to colorless. T his is the endpoint!
D eterm ine the percent saturation of D O using R ecord the num ber of digits on the D igital
T able 7-2 and the follow ing calculation m ethod: T itrator’s counter.
7. M ultiply the num ber on the counter by 0.01. T he result is the sam ple D O in m g/l.
7 Contact the DO monitors listed in this chapter for more information
about equipment or techniques needed in the titration process.
T able 7-2. O xygen solubility (saturation) in fresh w ater (m g/L )
Elevation Correction Water
Percent Saturation Table
Elevation Temperature C
Elevation in
Saturation Temperature C
Saturation
feet Factor 0.0 14.60 20.5 9.10 0 1.00 0.5 14.40 21.0 9.00 500
Dissolved Oxygen Protocol
7-5
Water Quality Monitoring Guidebook
A lternative M ethod U sing D O Probes
D epartm en t of E n viron m en tal Q uality. 1997. M eth odologies an d quality assuran ce procedures for
D O m eters are an altern ative m eth od for collectin g collectin g dissolved oxygen con cen tration data in data on w ater tem perature an d D O . H ow ever, D O surface w aters. Surface W ater Section , D E Q m eters are n ot as accurate as th e W in kler T itration
L aboratory. 17 pp.
M eth od an d m ay be subject to “ drift,” th us requirin g frequen t re-calibration . A useable m eter w ill be in
E PA . 1996. V olun teer m on itors guide to quality th e $1200 to $2000 price ran ge. For th ese an d oth er
assuran ce project plan s. E PA 841-B -96-003 reason s, usin g th e W rin kler T itration m eth od is
(Septem ber 1996). 60 pp.
probably m ore reliable for volun teer groups collectin g D O data in a cost effective, credible an d
H itch m an , M .L . 1978. M easurem en t of dissolved tim ely m an n er. For m ore in form ation about D O
oxygen . Joh n W iley & Son s an d O rpisph ere m eters, con tact th e m en tors listed in th is ch apter.
L aboratories, G en eva, Sw itzerlan d. 255 p. M cC ullough , D .A , an d E spin osa, F.A . 1996. A
m on itorin g strategy for application to
R eferences
salm on -bearin g w atersh eds. T ech n ical report 96-5.
A PH A . 1998. Stan dard m eth ods for th e exam in ation
C olum bia R iver In ter-T ribal C om m ission , Portlan d,