玉米样品经粉碎、过筛后,分取0.5 g,加入0.15 mol·L^-1硝酸溶液7 mL,置于微波消解仪中,分别在80,100,120℃下消解10,10,15 min。离心10 min,上清液过0.22 μm有机滤膜,滤液进入液相色谱仪,在Agilent ZORBAX SB-Aq反相色谱柱上用5 mmol·L^-1己烷磺酸钠-20 mmol·L^-1柠檬酸的混合溶液(pH 4.3)进行等度洗脱,分离后的4种砷形态{一甲基砷(MMA)、二甲基砷(DMA)、三价砷[As (Ⅲ)]和五价砷[As (Ⅴ)]}用电感耦合等离子体质谱仪测定。结果显示:4种砷形态可在4 min分离完全,质量浓度在2~50 μg·L^-1内与其对应的信号强度呈线性关系,检出限(3S/N)为0.041~0.054 μg·L^-1;对空白玉米样品进行3个浓度水平的加标回收试验,4种砷形态回收率为94.2%~102%,测定值的相对标准偏差(n=6)小于3.0%;方法用于3个天然污染玉米样品的分析,4种砷形态均有检出,其中As (Ⅲ)、As (Ⅴ)的检出量较高。

After corn sample was screened and sieved, an aliquot (0.5 g) was taken and mixed with 7 mL of 0.15 mol·L^-1 nitric acid solution. The mixture was placed into microwave digestion apparatus, and digested at 80, 100, 120 ℃ for 10, 10, 15 min, respectively. The supernatant was passed through a 0.22 μm organic filter membrane after centrifuging for 10 min. The filtrate was introduced into the liquid chromatography, and the mixed solution (pH 4.3) of 5 mmol·L^-1 sodium hexanesulfonate-20 mmol·L^-1 citric acid was used for isocratic elution on the Agilent ZORBAX SB-Aq reversed phase chromatographic column. The 4 arsenic species ［MMA, DMA, As(Ⅲ), As(Ⅴ)］ were determined by inductively coupled plasma mass spectrometry. It was shown that the 4 arsenic species could be separated completely within 4 min; the linear relationships between values of mass concentration and signal intensity were kept in the range of 2-50 μg·L^-1, and the detection limits (3S/N) were 0.041-0.054 μg·L^-1. Test for the spiked recovery was made on blank corn samples at three concentration levels, giving values of recovery in the range of 94.2%-102%, and RSDs (n=6) of the determined values were less than 3.0%. The proposed method was applied to the analysis of the 3 naturally polluted corn samples, and the 4 species of arsenic were all detected, among which the detection amounts of As(Ⅲ) and As(Ⅴ) were higher.