Simultaneous determination of nitrate and nitrite in biological samples by multichannel flow injection analysis

An automated method for the simultaneous determination of nitrite and nitrate in biological samples by using a multichannel flow injection analyzer has been developed. The method was based on the reaction of nitrite with Greiss reagent. The sample solution was injected and equally divided into two channels; channel one (1) represented total nitrite obtained by cadmium reduction of nitrate to nitrite while channel two (2) represented only nitrite. The absorbance of the color product was measured by photometric detectors with 540-nm filters. This method combines high reproducibility of sample introduction via flow injection and sensitivity of spectrophotometric detection. The detection limit is 25 nM for both nitrite and nitrate. The chemistry manifolds are constructed of Teflon tubing which, along with a low-pressure Flowfit connector system, provides for low maintenance, ease of use, and high sample throughput. We demonstrated that the system can be used for the determination of both nitrate and nitrite in a variety of biological samples as well as a comparison of the results from this system and the HPLC system.