Application of manganese(IV) dioxide microcolumn for determination and speciation of nitrite and nitrate using a flow injection analysis–flame atomic absorption spectrometry system

A flow injection (FI) method with flame atomic absorption spectrometry (FAAS) detection was developed for the determination and speciation of nitrite and nitrate in foodstuffs and wastewaters. The method is based on the oxidation of nitrite to nitrate using a manganese(IV) dioxide oxidant microcolumn where the flow of the sample through the microcolumn reduces the MnO2 solid phase reagent to Mn(II), which is measured by FAAS. The absorbance of Mn(II) are proportional to the concentration of nitrite in the samples. The injected sample volume was 400 μL with a sampling rate of analyses was 90 h−1 with a relative standard deviation better than 1.0% in a repeatability study. Nitrate is reduced to nitrite in proposed FI–FAAS system using a copperized cadmium microcolumn and analyzed as nitrite. The calibration curves were linear up to 20 mg L−1 and 30 mg L−1 with a detection limit of 0.07 mg L−1 and 0.14 mg L−1 for nitrite and nitrate, respectively. The results exhibit no interference from the presence of large amounts of ions. The method was successfully applied to the speciation of nitrite and nitrate in spiked natural water, wastewater and foodstuff samples. The precision and accuracy of the proposed method were comparable to those of the reference spectrophotometric method.