NEMI Method Summary

Method Summary Information

Method Number: I-2607 Media: WATER
Revision: Mar-90
Method Source: U.S. Geological Survey (USGS)
Subcategory: INORGANIC Analytes in this method
Official Name: Phosphorus, low ionic-strength water, colorimetry, phosphomolybdate, automated-segmented flow
Descriptive Name Phosphorus, dissolved, low ionic-strength, colorimetric, ASF
Source Info: USGS Branch of Information Services
Box 25286, MS 417
Federal Center
Denver, CO 80225-0286
Phone: 303-202-4700
Citation: U.S. Geological Survey Open-File Report 93-125
226219 Byte file
Brief Method
Summary:
 All forms of phosphorus, including organic phosphorus compounds, are converted to orthophosphate by an acid-persulfate digestion.
Orthophosphate ion reacts with ammonium molybdate in acidic solution to form phosphomolybdic acid, which upon reaction with ascorbic acid produces an intensely blue complex. Antimony potassium tartrate is added to increase the rate of reduction (Murphy and Riley, 1962; Gales and others, 1966; Pai and others, 1990).
Scope And
Application:
 This method is used to analyze samples of precipitation or natural water with a specific conductance of less than 100 uS/cm containing from 0.001 to 0.20 mg/L of phosphorus. Concentrations greater than 0.20 mg/L must be diluted. This method was implemented in the National Water Quality Laboratory in March 1990.
Applicable
Conc Range:
 0.001 to 0.200 mg/L
Interferences: Barium, lead, and silver interfere by forming a phosphorus precipitate but the effect is negligible in natural water. The interference from silica, which forms a pale blue complex, is small and may be considered negligible. Nitrite interferes but can be oxidized to nitrate with hydrogen peroxide before analysis. Residual chloride needs to be removed by boiling the sample.
Arsenic as arsenate(AsO4-3) produces a similar color as phosphate (Murphy and Riley, 1962) and might cause a positive interference. Arsenic concentrations as much as 100 ug/L do not interfere.
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.
Sample Handling: Container Description: 125 mL brown polyethylene bottle.
Treatment and Handling: Filter through 0.45 micron filter; use filtered sample to rinse container; preservation with mercuric chloride; chilled to 4 degrees C and ship immediately.
Max Holding Time:
 30 days
 
Relative Cost: Less than $50
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