AQUEOUS NITRITE ION DETERMINATION BY SELECTIVE REDUCTION AND GAS-PHASE NITRIC-OXIDE CHEMILUMINESCENCE

An improved method of now injection analysis for aqueous nitrite ion e xploits the sensitivity and selectivity of the nitric oxide (NO) chemi luminescence detector, Trace analysis of nitrite ion in a small sample (5-160 mu L) is accomplished by conversion of nitrite ion to NO by aq ueous iodide in acid, The resulting NO is transported to the gas phase through a semipermeable membrane and subsequently detected by monitor ing the photoemission of the reaction between NO and ozone (O-3) Chemi luminescence detection is selective for measurement of NO, and, since the detection occurs in the gas-phase, neither sample coloration nor t urbidity interfere. The detection limit for a 100-mu L sample is 0.04 ppb of nitrite ion. The precision at the 10 ppb level is 2% relative s tandard deviation, and 60-180 samples can be analyzed per hour, Sample s of human saliva and food extracts were analyzed; the results from a standard colorimetric measurement are compared with those from the new chemiluminescence method in order to further validate the latter meth od. A high degree of selectivity is obtained due to the three discrimi nating steps in the process: (1) the nitrite ion to NO conversion cond itions are virtually specific for nitrite ion, (2) only volatile produ cts of the conversion will be swept to the gas phase (avoiding turbidi ty or color in spectrophotometric methods), and (3) the NO chemilumine scence detector selectively detects the emission from the NO + O-3 rea ction. The method is free of interferences, offers detection limits of low parts per billion of nitrite ion, and allows the analysis of up t o 180 mu L-sized samples per hour, with little sample preparation and no chromatographic separation. Much smaller samples can be analyzed by this method than in previously reported batch analysis methods, which typically require 5 mt or more of sample and often need chromatograph ic separations as well.