Determination of nitrate and nitrite in vegetables by capillary electrophoresis with indirect detection

Abstract Nitrate and nitrite (and some other anions) were determined in vegetables by capillary electrophoresis (CE). The anions were extracted from the vegetables by mixing and diluting the samples with water at moderate temperature. The CE method is divided into two parts: a high-concentration-level method (for nitrate determination) and a low-concentration-level method (for nitrite determination). These CE methods were compared with a reference method (spectrophotometry after Jones reduction: official AOAC reference method for the determination of nitrates in foodstuffs). Parameters such as linearity, detection limit, quantification limit, precision and accuracy of the two techniques were investigated and compared. Both techniques resulted in acceptable linearity within their ranges. The detection limits of the CE methods were sufficiently low for the determination of the anions in vegetable samples. The precision and accuracy of the CE methods were comparable to those of the reference method. The precision was determined by evaluating the repeatability and the time-different intermediate precision, while the accuracy was investigated by comparing the slopes of the standard addition and external calibration lines and by evaluating the agreement between the results obtained with the CE and the reference spectrophotometric methods.