200 mL水样经硝酸（3+97）溶液0.1 mL酸解15 min。移取样品溶液5 mL，用硝酸（3+97）溶液定容至10 mL，用电感耦合等离子体质谱法（ICP-MS）测定总铬。另取样品溶液5 mL，依次加入pH 5的乙酸-乙酸钠缓冲溶液1 mL，30 g·L^-1的二乙基二硫代氨基甲酸钠溶液0.5 mL，1-己基-3-甲基咪唑六氟磷酸盐离子液体100 μL，于30℃超声处理15 min，离心。在下层有机相中加入2 mol·L^-1硝酸溶液2 mL，超声处理15 min，离心后，将上层液用硝酸（3+97）溶液定容至10 mL，用ICP-MS测定Cr（Ⅵ）。以总铬含量减去Cr（Ⅵ）含量得到Cr（Ⅲ）的含量。Cr（Ⅵ）和总铬的线性范围均为0~80 μg·L^-1，检出限（3s/k）分别为0.061，0.034 μg·L^-1。Cr（Ⅵ）的加标回收率在96.4%~105%之间，测定值的相对标准偏差（n=6）在2.1%~5.9%之间。

The sample (200 mL) was digested with 0.1 mL of HNO₃ solution (3+97) for 15 min. An aliquot (5 mL) of the sample solution was taken and diluted to 10 mL with HNO₃ solution (3+97), and total chromium was determined in this solution by ICP-MS. Another aliquot of 5 mL was taken from the sample solution, and 1 mL of pH 5 acetate buffer solution, 0.5 mL of 30 g·L^-1 sodium diethyldithiocarbamate solution and 100 μL of 1-hexyl-3-methylimidazolium hexafluorophosphate were added and the mixture was treated ultrasonically for 15 min at 30℃. After centrifuging, the lower organic phase was separated, and 2 mL of 2 mmol·L^-1 HNO₃ solution were added. The mixture was treated ultrasonically for 15 min. After centrifuging, the upper aqueous layer was separated and diluted to 10 mL with HNO₃ solution (3+97). Content of Cr(Ⅵ) was determined in this solution by ICP-MS. Content of Cr(Ⅲ) of the water sample was found by substracting value of Cr(Ⅵ) content from the total chromium. Linearity ranges of Cr(Ⅵ) and total chromium were same within 80 μg·L^-1 and values of D.L. (3s/k) were 0.061, 0.034 μg·L^-1 respectively. Recovery rates of Cr(Ⅵ) obtained by standard addition method were in the range of 96.4%-105% and the RSDs (n=6) were in the range of 2.1%-5.9%.