A. Cerda et al., SEQUENTIAL INJECTION SANDWICH TECHNIQUE FOR THE SIMULTANEOUS DETERMINATION OF NITRATE AND NITRITE, Analytica chimica acta, 371(1), 1998, pp. 63-71
An automated sequential injection system for monitoring nitrate and ni
trite in water samples is described. The method enables the simultaneo
us determination of both parameters with a single injection of sample.
A sandwich arrangement, in which the sample is placed between two Gri
ess reagent zones, is adopted. Nitrite is determined in one end of the
sample zone by diazotization-coupling reactions and spectrophotometri
c detection of the azo dye formed. In the other end, nitrate is simila
rly determined after its on-line reduction to nitrite using a copperis
ed cadmium column. The calibration is linear over the range 0.5-40 mu
mol l(-1) nitrite and 2-100 mu mol l(-1) nitrate, the mid-range relati
ve standard deviations being <2% in both the cases. Under optimised co
nditions the system has been applied to the determination of nitrate i
n tap, mineral and sea waters (the nitrite concentration was below the
detection limit) and the results have been compared with those obtain
ed by ion chromatography and a flow injection system based on the same
reactions. (C) 1998 Elsevier Science B.V. All rights reserved.