USGS Test Method I-2724


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Source:
USGS

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

Description:
Silver is determined by atomic absorption spectrophotometry in conjunction with a graphite furnace containing a graphite platform (Hinderberger and others, 1981). Whole water recoverable silver samples are evaporated to dryness and then brought back to volume with 0.1N HNO3 prior to introduction to the graphite furnace. 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.

Scope:
This method is used to determine silver in samples of water 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 10 ug/L. Sample solutions that contain silver concentrations greater than 10 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.The analytical range and detection limit can be increased or possibly decreased by varying the volume of sample injected or the instrumental settings.

Citation:
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:
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.Hydrochloric acid added to the water-suspended samples during the digestion process causes false silver signals. A concentration of 30 uL HCl per milliliter of water will cause false readings of 2 to 3 ug/L of silver.Concentrations increase proportionately with increased additions of HCl. Evaporate digested samples to dryness to remove excess HC1.Special precautionary measures to prevent contamination are 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 1 for every 10 samples.

Maximum Holding Time:
180 days

Media:
WATER

Subcategory:
Inorganic

Concentration:
1 to 10 ug/L

Precision:
Accuracy based on recovery of 1.6 ug/L added to a sample with an ambient 2.1 ug/L silver background concentration. Based on 6 replicates.

Detection:
Reporting Level defined as smallest measured concentration of a constituent that may be reliably reported using a given analytical method.

Revision Number:
May-89

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Analytical testing dots