Determination of nitrate ion concentration in fresh vegetable juices using ion-pair ultra performance liquid chromatography (IP-UPLC)

Abstract

The nitrate ion content of vegetables has become a human health concern. Accurate and fast tissue (root, stem or leaf stalk) testing in crops is a valuable tool to determine fertilizer needs and maximize fertilizer efficiency. Therefore, the nitrate ion concentrations in fresh vegetable juices were measured using ion-pair ultra performance liquid chromatography (IP-UPLC). The separation was performed on a C18 column with a mobile phase containing 0.15 mM tetrabutylammonium chloride as an ionpair reagent, 0.1% (w/v) ammonium acetate, and 5% (v/v) methanol at pH 6.2. The chromatogram was detected at 220 nm. The IP-UPLC chromatogram was obtained in 8 minutes, which is 39 minutes less than the time required to obtain a complete ion chromatography (IC) chromatogram of the same sample. The linearity of the method for nitrate ions was high, as evidenced by R2 of 0.9996. In nitrate-spiked samples of fresh vegetable juice, the recovery percent consistently approached 100%. Furthermore, the IP-UPLC results obtained without any preliminary sample cleanup were essentially identical to those obtained by IC with a correlation coefficient (R) of 0.999 (n = 10).