离子色谱法测定蔬菜中硝酸盐

Ion Chromatographic Determination of Nitrates in Vegetables

应用离子色谱法代替原用的镉还原法（即国标法）测定了蔬菜中硝酸根。离子色谱法的应用使测定的选择性、准确性、精密度和速度得到改善。蔬菜样品经捣碎,用自制的活性碳柱脱色和用微孔膜过滤等步骤的预处理后所得溶液即可进行离子色谱测定。所用色谱柱为IonpacAS14A-3C阴离子分离柱,淋洗液为Na2CO3和NaHCO3的混合溶液,洗出液中的NO3-经转化为游离酸（HNO3）后用电导检出器测定其导电率。在量程为30μS和进样液（50μL）中NO3-浓度在1.0～32.5 mg·L^-1的范围内,NO3ˉ离子峰高的积分值与进样液中NO3-浓度之间呈线性关系。用含不同浓度NO3ˉ离子的3种蔬菜按方法测定以检验其精密度,所求得RSD值（n=6）在0.7%～5.6%之间。经检验,方法的测定结果与镉还原法的结果之间无显著差异。

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 NO3ˉ in the introduced sample solution （50 μL） was obtained under the definite conditions of time of measuring distance of 30 tLS and concentration range of NO3ˉ 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 NO3ˉ 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.