取啤酒酵母样品0.200 0 g，用硝酸及过氧化氢微波消解，所得透明溶液蒸发至近干，冷却，加水溶解盐类。在pH 12的条件下滴加高锰酸钾溶液将铬（Ⅲ）氧化至六价，过量高锰酸钾滴加乙醇使还原褪色，用稀硝酸调节酸度到近中性。过滤，滤液定容至50 mL。取此溶液2.0 mL，置于25 mL容量瓶中，随后依次加入50 g·L^-1硫脲溶液2 mL，5 mol·L^-1磷酸溶液1.0 mL，0.2 mol·L^-1碘化钾溶液4.0 mL，10 g·L^-1聚乙烯醇溶液3.5 mL和0.5 g·L^-1瑞氏色素溶液4.0 mL，加水定容并摇匀。同时按相同操作制备试剂空白，但不加样品溶液。避光反应20 min，试样溶液中的铬（Ⅵ）在此体系中反应后导致瑞氏色素褪色。于波长662 nm处分别测得试样和空白溶液的吸光度A和A₀，并计算ΔA（A₀-A）。结果表明：ΔA与铬（Ⅵ）的质量浓度在0.40 mg·L^-1以内呈线性关系，检出限（3s/k）为0.005 5 mg·L^-1。实样的分析结果与原子吸收光谱法所测结果一致。测定值的相对标准偏差（n=5）在1.4%~2.3%之间，加标回收率在99.1%~102%之间。

The beer yeast sample (0.200 0 g) was digested with HNO₃ and H₂O₂ in microwave digestor. The clear solution obtained was evaporated to near dryness. The residue was taken up with water and its acidity was adjusted to pH 12. Solution of KMnO₄ was added dropwise to oxide Cr(Ⅲ) to Cr(Ⅵ) and excess of KMnO₄ was de-colorized by addition of few drops of C₂H₅OH. The solution was then neutralized by dilute HNO₃, filtered and its volume was made up to 50 mL. 2.0 mL of this sample solution were transfered to a 25 mL volumetric flask, and 2 mL of 50 g·L^-1 thiourea solution, 1.0 mL of 5 mol·L^-1 H₃PO₄ solution, 4.0 mL of 0.2 mol·L^-1 KI solution, 3.5 mL of 10 g·L^-1 PVA solution and 4.0 mL of 0.5 g·L^-1 Wright's stain solution were added in succession, and its volume was made up to 25 mL with water with thorough mixing. Simultanuously, a blank solution was prepared in the same way but without the addition of sample solution. The 2 solutions were set for 20 min in darkness. Due to the action of Cr(Ⅵ) in the reaction system, color-fading of Wright's stain was observed. Absorbance of sample solution (A) and blank solution (A₀) were measured at the wavelength of 662 nm, and ΔA were calculated by A₀-A. It was shown that linear relationship between values of ΔA and mass concentration of Cr(Ⅵ) was kept within 0.40 mg·L^-1, with detection limit (3s/k) of 0.005 5 mg·L^-1. In analysis of some substantial sample by this method, the results obtained were in consistency with those obtained by AAS. Values of RSDs (n=5) found were in the range of 1.4% to 2.3%. Test for recovery was made by the standard addition method, giving values of recovery in the range of 99.1% to 102%.