移取水样2.0 mL，用水定容至20.0 mL，加入1.0 mL硫酸（1+7）溶液，2.5 g·L^-1二苯碳酰二肼溶液1.0 mL，立即混匀。10.0 min后，依次加入24.0 g·L^-1溴化1-丁基-3-甲基咪唑溶液1.0 mL，24.0 g磷酸氢二钾，混匀后，进行双水相萃取，以3 500 r·min^-1转速离心2.0 min。将上层离子相移出，用水定容至3.0 mL，以试剂空白为参比液，于波长533 nm处测量吸光度。Cr （Ⅵ）的质量浓度在0.015~0.300 mg·L^-1内与其吸光度呈线性关系，检出限（3s/k）为7.8×10^-4mg·L^-1，富集倍数为6.67倍。方法应用于测定实际水样中的Cr （Ⅵ），加标回收率在95.3%~111%之间。

The water sample (2.0 mL) was diluted to 20.0 mL with water, then 1.0 mL of sulfuric acid (1+7) solution and 1.0 mL of 2.5 g·L^-1 diphenylcarbazide solution were added and mixed immediately. After 10.0 min, 1.0 mL of 24.0 g·L^-1 1-butyl-3-methylimidazolium bromide solution, 24.0 g dipotassium hydrogen phosphate were added in sequence, and then mixed well for aqueous two-phase extraction. Then the mixture was centrifuged at 3 500 r·min^-1 for 2.0 min. The upper ionic phase was taken, and made up to 3.0 mL with water. The absorbance at 533 nm was measured with blank sample solution as reference. Linear relationship was found between the absorbance and the mass concentration of Cr(Ⅵ) in the range of 0.015-0.300 mg·L^-1, with detection limit (3s/k) of 7.8×10^-4mg·L^-1 and enrichment factor of 6.67 times. The method was applied to determination of Cr(Ⅵ) in actual water samples, giving values of recovery obtained by standard addition method in the range of 95.3%-111%.