双波长分光光度法测定牛奶中的钙

采用双波长分光光度法测定牛奶中钙离子的含量。基于在碱性缓冲液中，钙与铬黑T（EBT）-聚乙二醇溶液作用形成1：1的配合物，利用等吸收双波长消去法，消除EBT自身的干扰。在558mn和645m处测定，得吸光度差△A，钙的质量浓度在0-4．8μg／mL范围内符合比耳定律，线性回归方程为△A=0．06964c＋0．00986，产0．9989。用干灰化法处理样品，通过测定样品的△4，查得样品中钙离子的含量。该方法测定结果的相对标准偏差为1．7％～7．6％（n=5）．平均加标回收率为79．0％～98．7％。

Determination of Calcium in Milk by Dual Wavelength Spectrophotometry

The calcium content in milk was detected by dual wavelength spectrophotometric method. Chrome black T（EBT） was used as the color reagent, in pH10.0 buffer solution of ammonia, calcium reacted with EBT-polyethylene glycol to form a stable complex（1 ： 1）. The interference of EBT was eliminated by double wave absorption and elimination technique. At wavelength of 558 nm and 645nm, the absorbance difference AA was detected and the calcium content obeyed Bee＇ s law in 0-4.8μg / mL. The linear regression equation was AA=0.069 64c ＋0.009 86, with correlation coefficient of 0.998 9. The sample was treated with dry ashing method, the content of calcium in the sample was abtained by detecting 21A. The relative standard deviation of this method was 1.7%-7.6% and the average recowry was 79.0%-98.7%.