A NOVEL FLOW-INJECTION SYSTEM FOR SIMULTANEOUS DETERMINATION OF NITRATE AND NITRITE BASED ON THE USE OF A ZINC REDUCTOR AND A BULK ACOUSTIC-WAVE IMPEDANCE DETECTOR

A novel flow-injection system has been developed for the simultaneous determination of nitrate and nitrite present in water, foodstuffs, and human saliva. The system is based on the use of a zinc-filled reducti on column and a bulk acoustic wave impedance sensor (BAWIS) as detecto r. With water as carrier stream, both nitrate and nitrite are converte d on-line to ammonia, whereas with sulfamic acid, only nitrate is conv erted to ammonia. The ammonia formed diffuses across a PTFE membrane a nd is trapped in an acid stream causing a change in the solution condu ctance, which is monitored by a BAWIS detector. At a throughput of abo ut 60 h(-1), the proposed system exhibited a linear response to the co ncentration of nitrate and nitrite from 2.5 mu M to 1.00 mM, with dete ction limits of 1.7 and 1.8 mu M, respectively, and the relative stand ard deviation of the peak heights (n = 6) ranged between 0.83 and 1.75 % for the entire working range. In analysis of real samples, the simul taneous determination of nitrate and nitrite was achieved by the propo sed method with a simple change of the carrier stream between water an d sulfamic acid, and the results agreed well with those of conventiona l colorimetry. (C) 1998 Academic Press.