USGS Test Method I-2138-89

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Method Name:
Cadmium in Water by GFAA, Dissolved. Official Name: Cadmium, Atomic Absorption Spectrophotometry, Graphite Furnace

Cadmium is determined by atomic absorption spectrophotometry in conjunction with a graphite furnace containing a graphite platform (Hinderberger and others, 1981). A sample is placed on the graphite platform and a matrix modifier is added. The sample then is evaporated to dryness, charred, and atomized using high-temperature ramping. The absorption signal produced during atomization is recorded and compared with standards.

This method is used to determine cadmium in samples of water and water-suspended sediment with a specific conductance not greater than 10,000 uS/cm. With Zeeman background correction and a 20-uL sample, the method is applicable in the range from 1 to 5 ug/L. Sample solutions that contain cadmium concentrations greater than 5 ug/L must be diluted or be analyzed by an alternate method. The analytical range and detection limit can be increased or possibly decreased by varying the volume of sample injected or the instrumental settings.

M.J. Fishman, 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of inorganic and organic constituents in water and fluvial sediments: U.S. Geological Survey Open-File Report 93-125

Interferences for samples with specific conductances less than 10,000 uS/cm normally are small. In addition, the use of the graphite platform reduces the effects of many interferences. Special precautionary measures to prevent contamination need to be used during sample collection and laboratory determination.

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 from sampling



1 - 5 (undiluted)

Analysis of five samples for dissolved cadmium by a single operator is as follows: for determinations with 5, 36, 5, 34 and 10 replicates the mean recovery is 1.1, 5.1, 5.2, 17.7 and 19.9 ug/L with standard deviations of 0.04, 0.2, 0.38, 1.88 and 0.94 ug/L, and %-RSD of 3.6, 3.9, 7.3, 10.6 and 4.7, respectively.

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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Analytical testing dots