AUTOMATED WATER ANALYSES

24.8. AUTOMATED WATER ANALYSES

Huge numbers of water analyses must often be performed in order to get mean- ingful results and for reasons of economics. This has resulted in the development of

a number of automated procedures in which the samples are introduced through a sampler and the analyses performed and results posted without manual manipulation of reagents and apparatus. Such procedures have been developed and instruments

marketed for the determination of a number of analytes, including alkalinity, sulfate,

Filter

Sampler Filtered sample

Buffer and indicator

Mixing coils Air

Proportioning pump

Colorimeter

Data processing and readout

Figure 24.9. Automated analyzer system for the determination of total alkalinity in water. Addition of a water sample to a methyl orange solution buffered to pH 3.1 causes a loss of color in proportion to the alkalinity in the sample.

Table 24.4. Chemical Parameters Commonly Determined in Water

Chemical species Significance in water Methods of analysis

Acidity Indicative of industrial pollution or Titration acid mine drainage

Alkalinity Water treatment, buffering, algal Titration productivity

Aluminum Water treatment, buffering AA, 1 ICP 2 Ammonia

Algal productivity, pollutant Spectrophotometry Arsenic

Toxic pollutant Spectrophotometry, AA, ICP

Barium Toxic pollutant AA, ICP Beryllium

Toxic pollutant AA, ICP, fluorimetry Boron

Toxic to plants Spectrophotometry, ICP Bromide

Seawater intrusion, industrial waste Spectrophotometry, potentiometry, ion chromatography

Cadmium Toxic pollutant AA, ICP Calcium

Hardness, productivity, treatment AA, ICP, titration Carbon dioxide

Bacterial action, corrosion Titration, calculation Chloride

Saline water contamination Titration, electrochemical, ion chromatography

Chlorine Water treatment Spectrophotometry Chromium

Toxic pollutant (hexavalent Cr) AA, ICP, colorimetry Copper

Plant growth AA, ICP Cyanide

Toxic pollutant Spectrophotometry, potentiometry, ion chromatography

Fluoride Water treatment, toxic at high Spectrophotometry, levels

potentiometry, ion chromatography

Hardness Water quality, water treatment AA, titration Iodide

Seawater intrusion, industrial waste Catalytic effect, potenti- ometry, ion chrom- atography

Iron Water quality, water treatment AA, ICP, colorimetry Lead

Toxic pollutant AA, ICP, voltammetry

Table 24.4 (Cont.)

Lithium May indicate some pollution AA, ICP, flame photometry

Magnesium Hardness AA, ICP Manganese

Water quality (staining) AA, ICP Mercury

Toxic pollutant Flameless atomic absorption

Methane Anaerobic bacterial action Combustible-gas indicator Nitrate

Algal productivity, toxicity Spectrophotometry, ion chromatography

Nitrite Toxic pollutant Spectrophotometry, ion chromatography

Nitrogen Proteinaceous material Spectrophotometry (albuminoid) (organic)

Organic pollution indicator Spectrophotometry Oil and grease

Industrial pollution Gravimetry Organic carbon

Organic pollution indicator Oxidation-CO 2 measurement

Organic Organic pollution indicator Activated carbon contaminants

adsorption Oxygen

Water quality Titration, electrochemical Oxygen demand

Water quality and pollution Microbiological-titration (biochemical)

(chemical) Water quality and pollution Chemical oxidation- titration

Ozone Water treatment Titration Pesticides

Water pollution Gas chromatography pH

Water quality and pollution Potentiometry Phenols

Water pollution Distillation-colorimetry Phosphate

Productivity, pollution Spectrophotometry Phosphorus

Water quality and pollution Spectrophotometry (hydrolyzable)

Potassium Productivity, pollution AA, ICP, flame photometry

Selenium Toxic pollutant Spectrophotometry, ICP, neutron activation

Silica Water quality Spectrophotometry, ICP Silver

Water pollution AA, ICP

Table 24.4 (Cont.)

Sodium Water quality, saltwater intrusion AA, ICP, flame photometry

Strontium Water quality AA, ICP, flame photometry

Sulfate Water quality, water pollution Ion chromatography Sulfide

Water quality, water pollution Spectrophotometry, titra- ion, chromatography

Sulfite Water pollution, oxygen Titration, ion scavenger

chromatography Surfactants

Water pollution Spectrophotometry Tannin, Lignin

Water quality, water pollution Spectrophotometry Vanadium

Water quality, water pollution ICP Zinc

Water quality, water pollution AA, ICP

1 AA denotes atomic absorption 2 ICP stands for inductively coupled plasma techniques, including atomic emission

and detection of plasma-atomized atoms by mass spectrometry. ammonia, nitrate/nitrite, and metals. Colorimetric procedures are popular for such

automated analytical instruments, using simple, rugged colorimeters for absorbance measurements. Figure 24.9 shows an automated analytical system for the determination of alkalinity. The reagents and sample liquids are transported through the analyzer by a peristaltic pump consisting basically of rollers moving over flexible tubing. By using different sizes of tubing, the flow rates of the reagents are proportioned. Air bubbles are introduced into the liquid stream to aid mixing and to separate one sample from another. Mixing of the sample and various reagents is accomplished in mixing coils. Since many color-developing reactions are not rapid,

a delay coil is provided that allows the color to develop before reaching the colorimeter. Bubbles are removed from the liquid stream by a debubbler pror to introduction into the flowcell for colorimetric analysis.