Samples for nitrate/nitrite and ammonium are collected together with a peristaltic pump and tubing and in-line filtered (through a 40 micron polycarbonate filter) into new, 20 ml HDPE plastic containers with conical caps. The samples are stored frozen until analysis, which should occur within 6 months. The samples are analyzed for nitrate/nitrite (and ammonium) simultaneously by automated colorimetric spectrophotometry, using a segmented flow autoanalyzer. Nitrate/nitrite is determined by utilizing the automated cadmium reduction method, as described in Standard Methods, where the absorption is monitored at 520 nm.
The detection limit for nitrate/nitrite is approximately 2 ppb and the analytical range for the method extends to 4000 ppb.
Method Log: Prior to January 2006 samples, nitrate/nitrite was determined on a Technicon segmented flow autoanalyzer. From 2006 to present, nitrate/nitrite is determined by an Astoria-Pacific Astoria II segmented flow autoanalyzer.
field & laboratory