National Water Quality Laboratory

Friday October 19, 2018

U.S. GEOLOGICAL SURVEY Open-File Report 93-449

Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory - Determination of Chromium in Water by Graphite Furnace Atomic Absorption Spectrophotometry

By Betty J. McLain

Graphite furnace atomic absorption spectrophotometry is a sensitive, precise, and accurate method for the determination of chromium in natural-water samples. The detection limit for this analytical method is 0.4 µg/L (microgram per liter) with a working linear limit of 25.0 µg/L. The precision at the detection limit ranges from 20 to 57 percent relative standard deviation (RSD) with an improvement to 4.6 percent RSD for concentrations greater than 3 µg/L.

Accuracy of this method was determined for a variety of reference standards that was representative of the analytical range. The results were found to be well within the established standard deviations. Samples were spiked with known concentrations of chromium with recoveries ranging from 84 to 122 percent. In addition, a comparison of chromium concentrations analyzed by graphite furnace atomic absorption spectrophotometry and direct-current plasma atomic emission spectrometry resulted in suitable agreement between the two methods, with an average deviation of 2.0 µg/L throughout the analytical range.

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