USGS-NWQL: I-4602: Phosphorus, orthophosphate plus hydrolyzable, total, colorimetric, ASF

Summary
Analytes
Revision
Data and Sites

Official Method Name

Phosphorus, orthophosphate plus hydrolyzable, colorimetric,phosphomolybdate, automated-segmented flow

Current Revision

1973

Media

WATER

Instrumentation

Automated Spectrophotometer

Method Subcategory

Inorganic

Method Source

USGS-NWQL

Citation

Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments, Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, Chapter A1 Edited by Marvin J. Fishman and Linda C. Friedman

Brief Method Summary

Polyphosphates (P₂O₇)^-4, (P₃O₁₀)^-5, etc., and a few organic phosphorus compounds are converted to orthophosphate by an acid hydrolysis.
Orthophosphate ion reacts with ammonium molybdate in acidic solution to form phosphomolybdic acid, which, upon reduction with ascorbic acid, produces an intensely colored blue complex. Antimony potassium tartrate is added to increase the rate of reduction (Murphy and Riley, 1962; Gales and others, 1966).
Mercuric chloride-preserved samples are fortified with a minimum of 85 mg/L NaCl to overcome the interference from mercury in the analysis.

Scope and Application

This method may be used to analyze most water-suspended sediment containing between 0.01 and 1.0 mg/L combined acid hydrolyzable and orthophosphate phosphorus. Samples containing greater concentrations need to be diluted.

Applicable Concentration Range

0.01 to 1.0 mg/L

Interferences

Barium, lead, and silver interfere by forming a phosphate precipitate, but the effect is usually negligible in natural waters. The interference from silica, which forms a pale-blue complex, is slight and can be considered negligible. Nitrite interferes, but can be oxidized to nitrate with hydrogen peroxide before analysis. Residual chlorine must be removed by boiling the sample.

Quality Control 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.

Sample Handling

Container Description: 125 mL brown polyethylene bottle.
Treatment and Handling: Use unfiltered sample to rinse container; preservation with mercuric chloride; chilled to 4 degrees C and ship immediately.

Maximum Holding Time

30 days

Relative Cost

Less than $50

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Phosphorus(7723-14-0) Black phosphorus P Phosphorous, Red Phosphorus Phosphorus (yellow or white) Red phosphorus Violet phosphorus White phosphorus Yellow phosphorus	0.010 mg/L	N/A	N/A

Precision Descriptor Notes:	It is estimated that the percent relative standard deviation for total orthophosphate plus hydrolyzable phosphorus will be equal to that reported for phosphorus by the automated phosphomolybdate method.
Detection Level Note:	Reporting Level defined as smallest measured concentration of a constituent that may be reliably reported using a given analytical method.

Revision	PDF/Link
1973

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USGS-NWQL: I-4602: Phosphorus, orthophosphate plus hydrolyzable, total, colorimetric, ASF

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