USGS-NWQL: I-1233: Chromium, dissolved, water, GFAA

Summary
Analytes
Revision
Data and Sites

Official Method Name

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

Current Revision

1993

Media

WATER

Instrumentation

Graphite Furnace-Atomic Absorption Spectrometer

Method Subcategory

Inorganic

Method Source

USGS-NWQL

Citation

McLain, Betty, 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of chromium in water by graphite furnace atomic absorption spectrophotometry: U.S. Geological Survey Open-File Report 93-449

Brief Method Summary

Chromium is determined by atomic absorption spectrophotometry in conjunction with a graphite furnace containing a pyrolytically coated tube and 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, pyrolized, and atomized using maximum-power heating. Maximum-power heating is a term associated with stabilized temperature platform furnace technology, which refers to a zero time ramp that allows for a 2,000^oC per second heating rate of the tube and creates the longest temperature lag between the platform and the tube wall (Carnrick and Slavin, 1989). The absorption signal produced during atomization is recorded and compared with standards.

Scope and Application

This method is applicable in the range from 0.5 to 25.0 ug/L of chromium in water and water-suspended sediment. Sample solutions that contain chromium in concentrations greater than 25.0 ug/L or have a specific conductance greater than 10,000 uS/cm will need to be diluted prior to analysis or analyzed by an alternate method.

Applicable Concentration Range

0.5-25 ug/L

Interferences

Refractive elements such as chromium have the potential to form carbides. The use of pyrolytically coated tubes and platforms (Fishman and Friedman, 1989, p. 169) improves sensitivity and reduces carbide formation and memory effect.
The use of pyrolytically coated tubes and platforms in conjunction with a matrix modifier reduces the potential for interferences. Multiple natural-water samples and Standard Reference Water Samples were spiked with known concentrations of chromium with no indication of signal suppression or enhancement. These samples contained major cation concentrations as great as 300 mg/L sodium, 200 mg/L calcium, 111 mg/L magnesium, and 20 mg/L potassium; and major anion concentrations with 620 mg/L sulfate and 210 mg/L chloride.

Quality Control Requirements

Calibrate instrument using calibration standards (CAL). Quality control sample (QCS), laboratory blank (LB), or standard (CAL) analyzed in every tenth cup. Analyze samples in duplicate (LD).

Sample Handling

Container Description: 250 mL Polyethylene bottle, acid-rinsed.
Treatment and Preservation: Filter through 0.45-um filter, use filtered sample to rinse containers and acidify sample with HNO₃ to pH < 2.

Maximum Holding Time

180 days

Relative Cost

$51 to $200

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Chromium(7440-47-3) Chromium Cr	0.500 ug/L	96% Rec (SL)	57.00			0.70 ug/L

Precision Descriptor Notes:	Precision based on 24 replicates analyzed over 15 days by a single operator.
Detection Level Note:	The method detection limit (MDL), using the procedure from the U.S. Environmental Protection Agency (1990, p. 537-539), is defined as the minimum concentration of a substance that can be measured and reported with 99 percent confidence that the analyte concentration is greater than zero. The theoretical detection limit was determined to be 0.5 ug/L, based on three times the standard deviation of multiple blank determinations. A chromium standard was prepared with a concentration of 1.0 ug/L (two times the theoretical detection limit). This standard then was analyzed ten times non-consecutively. From these data, a mean and a standard deviation were calculated (table 1) to determine the MDL. The MDL was determined to be 0.4 ug/L with a reporting limit of 0.5 + 0.1 ug/L.

Precision Descriptor Notes:

Precision based on 24 replicates analyzed over 15 days by a single operator.

Detection Level Note:

The method detection limit (MDL), using the procedure from the U.S. Environmental Protection Agency (1990, p. 537-539), is defined as the minimum concentration of a substance that can be measured and reported with 99 percent confidence that the analyte concentration is greater than zero. The theoretical detection limit was determined to be 0.5 ug/L, based on three times the standard deviation of multiple blank determinations. A chromium standard was prepared with a concentration of 1.0 ug/L (two times the theoretical detection limit). This standard then was analyzed ten times non-consecutively. From these data, a mean and a standard deviation were calculated (table 1) to determine the MDL. The MDL was determined to be 0.4 ug/L with a reporting limit of 0.5 + 0.1 ug/L.

Revision	PDF/Link
1993

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USGS-NWQL: I-1233: Chromium, dissolved, water, GFAA

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