Determination of trace nitrite by direct and indirect methods using differential pulse polarography and application

Trace nitrite determination plays an important role since it is being used in food-stuff as protecting agent. For this purpose, direct and indirect methods are developed using differential pulse polarography, DPP. It was found that in acidic medium nitrite was escaping as NO. In direct method, the peak of nitrite at about −1.43 V in pH 5 acetate buffer has been used. The calibration graph was linear in the concentration range of nitrite from 6 to 110 μM. No interference was observed from Pb, Zn, Cu, and Cd ions. However, Fe(III) had a peak very near to nitrite peak, this overlap could be eliminated by the addition of EDTA. The reaction between nitrite and sulfite has been used for indirect determination since sulfite peak at −0.7 V is sharp and very reproducible. It was found that sulfite concentration had to be 2.5–3 times larger than nitrite in order to have the reaction quantitative. The limit of quantification for nitrite in this medium was 2 × 10−6 M. The nitrite in sausage could be determined using both of these methods. While with direct method the result was 0.21 mg g−1, it was 0.24 mg g−1 with indirect method.