2002 Volume 51 Issue 12 Pages 1153-1158
A simple and highly sensitive method has been developed for the determination of nitrite at the nM level by adsorptive cathodic stripping voltammetry with a graphite electrode in an acidic solution. The optimized experimental conditions were as follows: nitrite was diazotized with sulfanilamide and coupled the resulting diazonium salt with 1-naphthylamine for 25 min to produce an azo dye; the azo compound was accumulated on a graphite electrode with stirring for 5 min on an open circuit; the deposit was then cathodically stripped in the potential range 0.2 to -0.2 V vs. SCE at a scan rate of 50 mV/s by a differential pulse mode in 0.4 M hydrochloric acid. A single well-defined cathodic peak was obtained at around -0.05 V vs. SCE, and nitrite was determined from the peak height in the stripping voltammogram. The calibration graph was linear over a concentration range of 1.1∼217 nM of nitrite (correlation coefficient>0.999) with a relative standard deviation (n=5) of 1.1% for 65 nM of nitrite. The detection limit (3σ), calculated from repeated determinations (n=20) of a blank solution, was 0.15 nM for an accumulation time of 5 min. The possible contamination due to the laboratory atmosphere was evaluated. By applying a non-electrolytic accumulation step, the maximum permissible concentrations of foreign elements in the determination of nitrite increased extremely. The proposed method was successfully applied to the determination of trace nitrite in commercial hydrochloric acid reagents. The time required for the whole procedure was within 35 min.
