USGS Test Method I-2667-85

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Method Name:
Selenium in water by atomic absorption, hydride, dissolved. Official Name: Selenium, atomic absorption spectrometric, hydride, automated

Organic selenium containing compounds are decomposed by hydrochloric acid-potassium persulfate digestion. The selenium so liberated, with the inorganic selenium originally present, is then reduced to the tetravalent state using a stannous chloride-potassium iodide mixture and is further converted to selenium hydride with sodium borohydride. The selenium hydride gas is stripped from the solution by a stream of nitrogen gas and conveyed to a tube furnace placed in the optical path of an atomic absorption spectrometer, where it is decomposed to atomic selenium. The optical absorbance is measured and related to the selenium concentration in the original sample. For additional information on the determination of selenium in water, see Goulden and Brooksbank (1974), and Pierce and others (1976).

This method may be used to analyze water containing at least 1 ug/L of selenium. Samples containing more than 15 ng/L need to be diluted.

Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments, Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, Chapter A1 Edited by Marvin J. Fishman and Linda C. Friedman

No interferences have been observed with the decomposition of selenium hydride in the tube furnace and its subsequent measurement. Goulden and Brooksbank (1974) reported no significant interferences in the digestion, reduction, and selenium hydride generation processes. Pierce and Brown (1976) reported interferences from trace elements commonly found in water at concentrations greater than 300 mg/L when sodium borohydride was introduced in the sample stream before hydrochloric acid. Nitric acid in excess of that usually added as a preservative in water and water suspended sediment samples, is reported to cause erratic results.

QC Requirements:
Quality-control samples area analyzed at a minimum of one in every ten samples. These QC samples include at least one of each of the following: blanks, quality control samples, third party check solutions, replicates, and spikes. Correlation coefficients for calibration curves must be at least 0.99. QC samples must fall within 1.5 standard deviations of the mean value. If all of the data-acceptance criteria in the SOPs are met, then the analytical data are acceptable.

Maximum Holding Time:
180 days after sampling



1.0-15.0 (undiluted)

Analysis of four samples for dissolved selenium five times each by one operator resulted in mean values of 3.3, 4.2, 6.4, and 8.5 mg/L and standard deviations of 0.1, 0.4, 0.2, and 0.1 mg/L, respectively. Precision for dissolved selenium may be expressed in terms of percent relative standard deviation: No. of replicates, Mean concentration (ug/L), and %-RSD: 5, 3.3, 3; 5, 4.2, 10; 5, 6.4, 3; 5, 8.5, 1.

Method detection limits (MDLs) were determined for this method using the procedures of the U.S. Environmental Protection Agency (1997).

Revision Number:

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