USGS-NWQL: I-1601-85: Phosphorus, orthophosphate, dissolved in water by colorimetry, phosphomolybdate

Summary
Analytes
Revision
Data and Sites

Official Method Name

Phosphorus, orthophosphate, dissolved by colorimetry, phosphomolybdate

Current Revision

1985

Media

WATER

Instrumentation

Colorimeter

Method Subcategory

Inorganic

Method Source

USGS-NWQL

Citation

Skougstad, M.W., Fishman, M.J., Friedman, L.C., Erdmann, D.E., and Duncan, S.S., eds., 1979, Methods for determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, chap. A1, 626 p.

Brief Method Summary

This method is no longer available through the USGS National Water Quality Laboratory. If using a local laboratory, refer to method report for more information.

Scope and Application

This method may be used to analyze most water and wastewater containing between 0.02 and 0.4 mg/L of orthophosphate-phosphorus. Samples containing greater concentrations need to be diluted.

Applicable Concentration Range

0.02-0.4 mg/L

Interferences

Barium, lead, and silver interfere by forming a precipitate. Silica produces a pale-blue color that is additive to the phosphate color, and may require correction. The effect of silica is somewhat dependent on the reagents; therefore, an appropriate silica correction should be determined for each batch of reagents. Nitrite interferes but can be oxidized to nitrate with hydrogen peroxide before analysis. Residual chlorine must be removed by boiling the sample. Mercuric chloride interferes when the chloride concentration is less than 50 mg/L. Mercuric chloride-preserved samples are fortified with a minimum of 85 mg/L NaCl to over come this interference. Arsenic as arsenate produces a color similar to that of phosphate and may cause a positive interference. Arsenic concentrations as much as 100 ug/L do not interfere.

Quality Control Requirements

Sample Handling

Maximum Holding Time

Relative Cost

Unknown

Sample Preparation Methods

This method has 2 analytes associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Phosphate(14265-44-2) Orthophosphate Orthophosphate, total Phosphate Phosphorus (as phosphate) Phosphorus, phosphate, ortho Reactive phosphorus Total orthophosphate Total phosphorus	N/A	N/A	N/A
Phosphorus(7723-14-0) Black phosphorus P Phosphorous, Red Phosphorus Phosphorus (yellow or white) Red phosphorus Violet phosphorus White phosphorus Yellow phosphorus	N/A	N/A	11.00			0.41 mg/L

Precision Descriptor Notes:	Inactive method; included for informational purposes as it is approved by EPA for regulatory use but no longer used by the USGS.
Detection Level Note:	Method can be use to detect orthophosphate-phosphorus between 0.02 and 0.4 mg/L. Samples containing greater concentrations need to be diluted.

Revision	PDF/Link
1985

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USGS-NWQL: I-1601-85: Phosphorus, orthophosphate, dissolved in water by colorimetry, phosphomolybdate

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