SIMULTANEOUS DETERMINATION OF NITRATE AND NITRITE ION BY MICRO-FLOW INJECTION-ANALYSIS

To minimize the sample size, reagent consumption and waste, a micro-no w injection analysis (mu FIA) was investigated and applied to the simu ltaneous determination of nitrate and nitrite ion in water samples. A double-plunger micropump was used to propel a carrier and a chromogeni c solution; each flow rate was 50 mu l min(-1), and the delivery volum e was 2.5 mu l per stroke. Nitrate was reduced to nitrite on line by p assing through a mini column (0.53 mm i.d. x 5 cm) packed with powdere d Cd/Cu (60 similar to 80 mesh). The reduction efficiency was 99% usin g this reduction column. Detection was carried out at 538 nm with a li ght-emitting diode used as an azo dye. The carrier solution contained EDTA and NaCl (pH 8.1 similar to 8.4) and the reagent solution contain ed sulfanilamide, N-(1-naphthyl) ethylenediamine and HCl. For a simult aneous determination, the sample injected into the carrier stream was split into two streams: one passed through the mini Cd/Cu column; the other passed through a bypass column packed with grass beads. The samp le zone passing through the bypass column gave a first peak derived fr om nitrite; the other sample zone passing through the reduction column gave the second peak derived from nitrate and nitrite. The detection limits of nitrate and nitrite were about 1 x 10(-7) M using the propos ed simultaneous determination system.