Continuous Flow Colorimetric Assay for Total N Digests

Last revised July 22, 1997

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[Appropriate samples]

[Details of the method]

[Sample preparation and handling]

The color reaction chemistry used in this process is appropriate for liquid samples in which nitrate-N and nitrite-N are 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 NO2+NO3-N procedure is specified in replicable detail in [assay for Nitrate/Nitrite].

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.