12 Extraction Techniques for the Determination of Cobalt, Nickel, and Lead in Fresh Water by Atomic Absorption M A R V I N J. F I S H M A N and M A R Y L A N D R. M I D G E T T Downloaded by UNIV OF OTTAWA on April 17, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0073.ch012
U . S. Geological Survey, Denver, Colo.
The detection limits for cobalt, nickel, and lead in aqueous solution by atomic absorption are about 50 μg. per liter. Nor mally these elements occur at lower concentrations in fresh waters, and direct measurement by atomic absorption is not possible. A rapid, simple, accurate, and sensitive chelation -extraction method for determining lead, cobalt, and nickel is attained by chelating the metals with ammonium pyr rolidine dithiocarbamate at a pH of 2.8, extracting the metal-chelates with methyl isobutyl ketone, and aspirating the ketone layer. Results obtained by this method agreed well with results obtained by spectrographic methods. As little as 1 μg. of lead, cobalt, and nickel per liter can be de tected. This is at least one order of magnitude lower than most other wet chemical procedures.
A tomic absorption is being used routinely for the direct determination of sodium, potassium, calcium, magnesium, and several trace elements: strontium, lithium, manganese, copper, and zinc i n natural waters (4). There is ordinarily no need to concentrate these trace elements since most waters contain detectable amounts. However, certain other trace elements, such as cobalt, nickel, and lead normally occur i n fresh waters at concentrations less than can be detected by atomic absorption directly. Table I shows the minimum, maximum, and median concentrations for lead, cobalt, and nickel i n the water supplies of the 100 largest cities i n the United States ( 3 ) . Spectrographic methods were used to obtain these data. Only nine samples contained detectable concentrations of cobalt. The highest concentration was 9.5 μg. per liter, whereas the cobalt found in the other samples were listed as "less-than" values. Ninety-five per cent 230
Baker; Trace Inorganics In Water Advances in Chemistry; American Chemical Society: Washington, DC, 1968.
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Extraction Techniques
of the water supplies contained less than 10 μg. per liter of both nickel and lead. The detection limits for lead, cobalt, and nickel by atomic absorption are approximately 50, 30, and 20 /tg. per liter, respectively. These detection limits were determined with a Perkin-Elmer Model 303 atomic absorption spectrophotometer by aspirating aqueous standards. A preconcentration procedure is, therefore, essential if these elements are to be determined b y atomic absorption. Table I.
Concentration of Lead, Cobalt, and Nickel in Public Water Supplies of the 100 Largest Cities in the United States
Downloaded by UNIV OF OTTAWA on April 17, 2016 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0073.ch012
1
Minimum Pb Co Ni
ND* ND* ND*
Maximum
Median
62.0 9.5 34.0
3.7 ND*
