Simultaneous flow injection determination of nitrate and nitrite in water by gas-phase chemiluminescence

A reagent-injection flow injection procedure for the determination of nitrate and nitrite in water by reduction to NO followed by a membrane separation process and chemiluminescence detection, with air-stripping, is proposed. Microporous PTFE was used as a membrane to transfer NO to the gas phase after reducing nitrate and nitrite with Ti(III) and nitrite alone by iodide in acidic media. Chemiluminescence (CL) peak height signals produced by the reaction of NO with ozone were linearly proportional to concentrations from 5 μg NI as nitrate and 3 μg NI as nitrite to around l mg NI. The relative standard deviation (n = 5) was 1.2% at 0.70 mg NI nitrate and 1.4% at 0.28 mg NI nitrite. The response time from injecting the reducing agent until the signal reached a peak was 1.0 min. In the presence of nitrite, nitrate could be determined from the difference between the CL intensity in the Ti(III) and iodide systems.