EXAMPLE: Nitrate assay
The determination of nitrate and nitrite is one of the most frequently performed assay on soil and water samples.
This colorimetric assay is based on reduction of nitrate to nitrite on Cd column, followed by reaction of nitrite with sulfanilamide. (Gries reaction) .The thus produced azo dye is quantified by spectrophotometry @ 540nm.
The attached readout, obtained at a constant flow rate (cFI) mode, shows a calibration record of 0, 2, 5, and 8 ppM nitrate, followed by a routine run of nitrate assay in samples of soil extracts. The sampling rate is 35 s/hr and detection limit is 1 ppM N. Compare this (cFI) widely used routine assay with the programed flow (pFI ) method 1.2.33.
1.3.2.
