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.