Flow Injection Determination of Nitrite in Food Samples by Dialysis Membrane Separation and Photometric Detection

An on-line dialysis preconcentration determination of nitrite by injection method has been developed. In this paper, the polyetherimide-composed membranes (PEI) were used for the dialysing of the nitrite from the food samples matrix, because they showed a high dialysing yield and analytical signal, low blank signal and absence of membrane clogging. In the recipient (acceptor) stream, the nitrite which penetrated from the PEI membrane, is diazotised with sulphanilamide to form a diazonium action, which is supsequently coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 525 nm. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dialysing membranes, and interfering species were studied. The calibration curve was between 12.5 ng ml-1 and 3.2 µg ml-1, and the detection limit was 4.5 ng ml-1, and up to 15 samples can be analyzed per hour with a relative precision of ca.2.8%. The proposed method was successfully applied to the determination of nitrite in food samples with satisfactory results.