Tan H S, McKibben D M, Glasser A C
J Pharm Sci. 1981 Jun;70(6):693-5. doi: 10.1002/jps.2600700634.
A modification of the USP method for the assay of systemic alkalizer solutions containing mixtures of citrate and citric acid is presented; it involves two titrations and ion-exchange chromatography. A diluted sample is tritiated with 0.02 N NaOH to find the free citric acid content. The eluate from cation-exchange chromatography of an equal volume of diluted sample is titrated with 0.02 N NaOH to assay for total citric acid. Subtracting the results of the first titration from the second provides the citrate content. Synthetic mixtures of potassium citrate-citric acid, potassium citrate-sodium citrate-citric acid, and sodium citrate-citric acid were prepared and assayed. The method was applied to commercially available preparations. The proposed method eliminates some significant errors of the compendial method, and the accuracy and reproducibility are equal or better than those obtained with the compendial method. Theoretically, the result obtained by the compendial method does not necessarily give the citrate content.
本文介绍了美国药典中测定含有柠檬酸盐和柠檬酸混合物的全身用碱化剂溶液方法的一种改进；该方法涉及两次滴定和离子交换色谱法。取一份稀释后的样品，用0.02N氢氧化钠滴定，以测定游离柠檬酸含量。取等体积稀释样品进行阳离子交换色谱分析，其洗脱液用0.02N氢氧化钠滴定，以测定总柠檬酸含量。用第二次滴定结果减去第一次滴定结果，即可得到柠檬酸盐含量。制备并分析了柠檬酸钾 - 柠檬酸、柠檬酸钾 - 柠檬酸钠 - 柠檬酸和柠檬酸钠 - 柠檬酸的合成混合物。该方法应用于市售制剂。所提出的方法消除了药典方法中的一些重大误差，其准确性和重现性与药典方法相当或更好。从理论上讲，药典方法得到的结果不一定能得出柠檬酸盐含量。
