USGS Test Method I-2243

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Method Name:
Cobalt, dissolved, water, GFAA. Official Name: Cobalt, atomic absorption spectrophotometry, graphite furnace

Cobalt 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 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 cobalt 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 25 ug/L. Sample solutions that contain cobalt concentrations greater than 25 ug/L must be diluted or be analyzed by an alternate method. This method was implemented in the National Water Quality Laboratory in May 1989.

Methods for the Determination of Radioactive Substances in Water and Fluvial Sediments, USGS TWRI Book 5, Ch. A5

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:
Calibrate instrument using calibration standards (CAL). Quality control samples (QCS) and laboratory blanks (LB) analyzed at a minimum of I each after every 10 samples. (Reference OFR 95-443).

Maximum Holding Time:
180 days



1-25 ug/L

Precision based on 6 replicates of a sample by a single operator.

The analytical range and detection limit can be increased or possibly decreased by varying the volume of sample injected or the instrumental settings.

Revision Number:
Revised 1989

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