NEMI Method Summary

Method Summary Information

Method Number: I-3239 Media: WATER
Revision: Revised 1985
Method Source: U.S. Geological Survey (USGS)
Subcategory: INORGANIC Analytes in this method
Official Name: Cobalt, atomic absorption spectrometric, direct
Descriptive Name Cobalt, total-recoverable, water, FLAA
Source Info: USGS Branch of Information Services
Box 25286, MS 417
Federal Center
Denver, CO 80225-0286
Phone: 303-202-4700
Citation: USGS Methods, Volume A1
115669 Byte file
Brief Method
Summary:
 Cobalt is determined by atomic absorption spectrometry by direct aspiration of the sample into an air-acetylene flame without additional treatment of the sample other than the addition of ammonium chloride to mask certain interferences.
Scope And
Application:
 This method may be used to analyze water and water-suspended sediment containing at least 50 ug/L of cobalt. Samples solutions containing more than 1,000 ug/L need either to be diluted or to be read on a less expanded scale. Sample solutions containing less than 50 ug/L need to be analyzed by the atomic absorption spectrometric chelation-extraction method, providing the interference limits discussed in that method are not exceeded.
Total recoverable cobalt in water-suspended sediment needs to undergo preliminary digestion-solubilization by method I-3485, and recoverable cobalt in bottom material needs to undergo preliminary digestion-solubilization by method I-5485 before being determined.
Applicable
Conc Range:
 50-1000 ug/L
Interferences: Nitrate at 1 mg/L interferes by suppressing the absorption of the cobalt. This interference is eliminated in solutions containing about 18,000 mg/L of ammonium chloride. Samples adjusted to this concentration of ammonium chloride show no interference from 800 mg/L of nitrate.
Individual concentrations of sodium (9,000 mg/L), potassium (9,000 mg/L), calcium (4,500 mg/L), magnesium (4,500 mg/L), sulfate (9,000 mg/L), chloride (15,000 mg/L), iron (4 X 106 ug/L), and cadmium, nickel, copper, zinc, lead, and chromium (10,000 ug/L) do not interfere. Higher concentrations of each constituent were not investigated.
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).
Sample Handling: Container Description: 250 mL Polyethylene bottle, acid-rinsed.
Treatment and Preservation: Use unfiltered sample to rinse bottles, then acidify collected sample with HNO3 to pH < 2.
Max Holding Time:
 180 days
Sample Prep Met I-3485
Relative Cost: Less than $50
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