Continuous Flow Colorimetric Assay for ortho-Phosphate

Last revised July 22, 1997

Page contents: (click to skip down)

[Appropriate samples]

[Details of the method]

[Sample preparation and handling]

The color reaction chemistry used in this process (automated Murphy/Riley 1962) is appropriate for water samples containing native ortho-phosphate and for other liquid samples in which ortho-P is present as the product of a digest or extract procedure.

A discussion of principles and practical considerations in continuous-flow colorimetry is available in the [Colorimetry Overview] document. The ortho-PO4 procedure is specified in replicable detail in [assay for Phosphorus-all forms].

Samples must be free of turbidity and particulate matter and must not contain any color that absorbes at the same wavelength as the analytical color chemistry tint. Liquid samples which cannot be analyzed immediately after collection must be preserved for shipment. The U.S. E.P.A. has published a table of [acceptable preservation methods] and holding times for many analytes. Detailed sample-handling instructions specific to this laboratory are available in the [Sample collection] instructions.