Hoebus J, Roets E, Hoogmartens J
Laboratorium voor Farmaceutische Chemie en Analyse van Geneesmiddelen, Faculteit Farmaceutische Wetenschappen, Katholieke Universiteit Leuven, Belgium.
J Pharm Biomed Anal. 1996 Dec;15(3):359-64. doi: 10.1016/s0731-7085(96)01865-1.
Phenoxymethylpenicilloic acid monohydrate was titrated with 12 different brands of Karl Fischer reagent. It was shown that only the four pyridine-containing reagents gave correct results for water content, providing that the sample solution was cooled in an ice bath or that the delay time of the amperometric end-point determination was 10 s instead of 30 s, as prescribed by the European Pharmacopoeia. The other reagents always gave results, which were too high. When these reagents were used to titrate the water in sodium amoxicillin, sodium carbenicillin or sodium ticarcillin the same conclusions could be drawn with regard to the accuracy of the results, the usefulness of the reagents and the reaction conditions. These penicillins may contain up to 9% penicilloic acids. The maximum relative error obtained with pyridine-free reagents was about 50% for ticarcillin. It has been confirmed that penicilloic acids interfere with Karl Fischer titration of water and that this interference is greatly dependent on the brand of reagent and on the reaction conditions.
用12种不同品牌的卡尔费休试剂对一水合苯氧甲基青霉素酸进行滴定。结果表明，只有四种含吡啶的试剂能给出正确的水分含量结果，前提是样品溶液在冰浴中冷却，或者安培终点测定的延迟时间为10秒，而不是欧洲药典规定的30秒。其他试剂给出的结果总是偏高。当用这些试剂滴定阿莫西林钠、羧苄西林钠或替卡西林钠中的水分时，就结果的准确性、试剂的实用性和反应条件而言，可以得出相同的结论。这些青霉素可能含有高达9%的青霉素酸。对于替卡西林，无吡啶试剂获得的最大相对误差约为50%。已经证实，青霉素酸会干扰卡尔费休法对水的滴定，并且这种干扰在很大程度上取决于试剂的品牌和反应条件。
