Ion Chromatographic Determination of Nitrates in Vegetables

The conventional cadmium-reduction method for the determination of nitrates in vegetables was substituded by the ion chromatographic (IC) method to improve accuracy,precision selectivity,and rapidity of determination.The vegetable sample was pretreated by pounding to pieces,de-colorizing by passing through the self-made active carbon column and removing solid particles by filtering through microporous membrane.The Ionpac AS14A-SC anion separation column and an eluant of mixed solution of Na2CO3 and NaHCO3 were used in the separation of anions.Nitrate in the eluate was transformed into free acid (HNO3) and its conductivity was measured with conductance detector.Linear relationship between the integration values of peak height and the concentration of NO-3 in the introduced sample solution (50 μL) was obtained under the definite conditions of time of measuring distance of 30 μS and concentration range of NO-3 in the introduced sample solution of 1.0-32.5 mg·L-1.Precision of the IC-determination was tested with 3 kinds of vegetables containing NO-3 in different concentrations,and values of RSD′s (n=6) obtained were in the range of 0.7%-5.6%.Analytical results obtained by this method checked quite well with those obtained by the standard method.