果胶的咔唑硫酸分光光度测定法研究

Spectrophotometric Method for the Determination of Pectin with Carbazole and Sulphuric Acid

对咔唑硫酸光度法测定果胶粉的水解产物──半乳糖醛酸的条件进行了研究。结果表明，在 ０．０３５～０.０４０ ｇ果胶粉中加入８～１２ｍＬ ０.５ ｍｏｌ／Ｌ的稀硫酸和１５ ｍＬ蒸馏水，当温度控制在 ６５～８０℃时，果胶粉在 １５～２０ ｍｉｎ内完全水解。水解产物半乳糖醛酸在浓硫酸介质中与咔唑形成稳定的紫红色络合物，λ｛ｍａｘ｝＝５４０ ｎｍ，显色时间为１．５ ｈ ３０ ｍｉｎ，ε'＝１．３８ｘ１０３Ｌ（ｍｏｌ·ｃｍ）。在０～１００ｍｇ／Ｌ浓度范围内与吸光度成线性关系，相对标准偏差＝１．３２％，回收率为９６％～１０７％，用于实际样的测定时，结果满意。

The reaction conditions for the-system of carbazole, sulphric acid and galacturonic acid, Which is the hydrolysate of pectin, have been investigated. The pectin can be completely hydrolyzed over the time range 15-20 min in the mixture of 8-12 mL 0.5 mol/L sulphuric acid and 15 mL distilledwater in the temperature range of 65-80℃. The galacturonic acid can form the stable purlish red complex in the presence of sulphuric acid. The complex, having the maximum absorption wavelength at 540 nm, shows a constant absorption intensity in 1.5 h and the molar adsorptian coefficient is 1.38×103 L/moL.cm. Under the optimal experimental conditions, absorption intensity is linear function of concentration of galacturonic acid in the range of 0-100μg/mL with a relative standard deviation 1.32 % and the recovery is in the range of 96.0 %-107.0 %. The method has been applied successfully to the actual samples.