卡托普利分子中的巯基(-SH)能还原三价铁至二价状态,试验发现铁(Ⅲ)与钛铁试剂络合物的色泽由于卡托普利的存在而出现消褪。确定了铁(Ⅲ)与钛铁试剂的反应条件:于25 mL的容量瓶中依次加入0.250 0 g·L-1铁(Ⅲ)溶液2.20 mL,6.25 g·L-1钛铁试剂溶液0.6 mL及pH 3.0 Clark-Lubs缓冲溶液10.0 mL,加水定容,于80 ℃水浴中加热20 min使显色完全。在其吸收峰670 nm处测量吸光度A1。在此反应体系中加入不同浓度的卡托普利标准溶液,按相同步骤操作并测得其吸光度A2,结果表明:A1与A2之差(ΔA)与卡托普利的质量浓度在0.012~0.036 g·L-1范围内呈线性关系。将此方法应用于卡托普利片剂中卡托普利含量的测定,所得测定值与用药典法测定的结果相符。

It was shown that the -SH group in molecules of captopril (CTPR) exhibits the property of reduction of Fe(Ⅲ) to Fe(Ⅱ), and that the color of complex formed between Fe(Ⅲ) and tiron is extincted by the presence of CTPR. Conditions for color reaction between Fe(Ⅲ) and tiron were taken as follows: in a 25 mL volumetric flask, 2.20 mL of 0.250 0 g·L-1 Fe(Ⅲ) solution, 0.6 mL of 6.25 g·L-1 tiron solution and 10.0 mL of Clark-Lubs buffer solution of pH 3.0 were added and water was added to make up the volume to 25 mL. The reaction mixture was heated in water bath at 80 ℃ for 20 min for completion of the color reaction. After cooling absorbance (A1) of the solution is measured at its absorption maximum of 670 nm. Standard solutions of CTPR with various concentrations were added to solutions of the color reaction system described above and operated in the same way. Values of absorbance (A2) were measured, and linear relationship between values of ΔA(A1-A2) and mass concentration of CTPR was kept in the range of 0.012-0.036 g·L-1. The above procedure was applied to determination of CTPR in its tablets, giving results in consistency with the values found by the method of pharmacopoeia.