Abstract
Adsorptive cathodic stripping voltammetry (CSV) is used for the determination of nitrite in natural waters, including sea water. The nitrite is first derivatised by diazotization with sulphanilamide, followed by coupling to 1-naphthylamine to produce an azo dye. This azo dye adsorbs on the mercury drop electrode and its reduction is fully reversible. The concentration of the dye is linearly related to the height of the reduction peak for nitrite concentrations between 0.3 and 200 nM. The optimal concentrations of sulphanilamide and naphthylamine are 2 mM and 0.1 mM, respectively, at a pH of 2.5. After diazotization and coupling, the differential-pulse CSV of the azo dye is done at pH 8.4 with an adsorption potential of −0.3 V. The standard deviation of a determination of 4 nM nitrite is ±2% and the limit of detection is 0.3 nM for an adsorption time of 60 s. The linear range can be extended by using shorter adsorption times. These sensitivity in sea water is the same as that in fresh water. The concentration of the dye can also be measured by using anodic stripping voltammetry preceded by adsorptive collection at −0.7 V, but this procedure is less sensitive than CSV.
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