Hach Co.: 8048: Orthophosphate by Colorimetry

Summary
Analytes
Revisions
Data and Sites

Official Method Name

Phosphorous, Reactive - Ascorbic Acid Method

Current Revision

Revised 1999; USEPA Accepted: May 1, 1999

Media

WATER

Instrumentation

Spectroscopy (Colorimetry; Photometry)

Method Subcategory

Inorganic

Method Source

Hach Co.

Citation

1997 Edition of the Hach Water Analysis Handbook

Brief Method Summary

Ammonium molybdate and antimony potassium tartrate react in an acid medium (potassium pyrosulfate) with dilute solutions of phosphorus to form a yellow colored antimony-phospho-molybdate complex. This complex is reduced to an intensely blue-colored (molybdenum blue) complex by ascorbic acid. This color is proportional to the phosphorus concentration. All reagents for this reaction are contained in PhosVer 3 Phosphate Reagent.

Scope and Application

Applicable to water, wastewater and seawater.

Applicable Concentration Range

0 - 5.0 mg/L Phosphate (1.7 mg/L as Phosphorous)

Interferences

Arsenate reacts with the molybdate reagent to produce a blue color similar to that formed with phosphate. Concentrations as low as 0.1 mg/L as interfere with the phosphate determination.
Sulfide (Na₂S) and silicate do not interfere at concentrations of 1.0 and 10.0 mg/L, respectively.
Hexavalent chromium and NO2- interfere to give results about 3% low at concentrations of 1 mg/L and 10 to 15% low at concentrations of 10 mg/L.
Large amounts of turbidity may cause inconsistent results in the phosphate tests because the acid present in the powder pillow may dissolve some of the suspended particles and because of variable desorption of orthophosphate from the particles. For highly turbid or colored samples, add the contents of one Phosphate Pretreatment Powder Pillow to 25 mL of sample. Mix well. Use this solution to zero the instrument.

Quality Control Requirements

Analysis of standards for accuracy check. Also, the Hach Water Handbook contains a general discussion of QC practices.

Sample Handling

If prompt analysis is impossible, preserve samples by filtering immediately and storing the sample at 4^oC for a maximum holding time of 48 hours in either plastic or glass.

Maximum Holding Time

48 hours.

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
Phosphate(14265-44-2) Orthophosphate Orthophosphate, total Phosphate Phosphorus (as phosphate) Phosphorus, phosphate, ortho Reactive phosphorus Total orthophosphate Total phosphorus	0.004 mg/L	95% Rec (SL)	1.00 % RSD (SL)			1.00 mg/L

Precision Descriptor Notes:	Precision and accuracy values are based on replicate analyses of a sample in a single laboratory.
Detection Level Note:	MDL was determined per 40 CFR 136, Appendix B.

Revision	PDF/Link
Revised 1999; USEPA Accepted: May 1, 1999
1998

The Water Quality Portal contains sample results from sites that use this method.

Download WQP data

Select data:

Sites only
Sample results only

File format:

Comma-separated
Tab-separated
MS Excel 2007+

Sites where this method was used

Loading Sites ...

Hach Co.: 8048: Orthophosphate by Colorimetry

WHO WE ARE

LEGAL