GlaxoSmithkline Consumer Healthcare, St Georges Avenue, Weybridge, Surrey KT13 0DE, UK.
Talanta. 2002 Dec 6;58(6):1301-10. doi: 10.1016/s0039-9140(02)00421-6.
4-Aminophenol (4AP) is the primary degradation product of paracetamol which is limited at a low level (50 ppm or 0.005% w/w) in the drug substance by the European, United States, British and German Pharmacopoeias, employing a manual colourimetric limit test. The 4AP limit is widened to 1000 ppm or 0.1% w/w for the tablet product monographs, which quote the use of a less sensitive automated HPLC method. The lower drug substance specification limit is applied to our products, (50 ppm, equivalent to 25 mug 4AP in a tablet containing 500-mg paracetamol) and the pharmacopoeial HPLC assay was not suitable at this low level due to matrix interference. For routine analysis a rapid, automated assay was required. This paper presents a highly sensitive, precise and automated method employing the technique of Flow Injection (FI) analysis to quantitatively assay low levels of this degradant. A solution of the drug substance, or an extract of the tablets, containing 4AP and paracetamol is injected into a solvent carrier stream and merged on-line with alkaline sodium nitroprusside reagent, to form a specific blue derivative which is detected spectrophotometrically at 710 nm. Standard HPLC equipment is used throughout. The procedure is fully quantitative and has been optimised for sensitivity and robustness using a multivariate experimental design (multi-level 'Central Composite' response surface) model. The method has been fully validated and is linear down to 0.01 mug ml(-1). The approach should be applicable to a range of paracetamol products.
对乙酰氨基酚（4AP）是扑热息痛的主要降解产物，在药物中其含量被《欧洲药典》、《美国药典》、《英国药典》和《德国药典》限制在低水平（50ppm 或 0.005%w/w），采用手动比色限量试验。片剂产品专论中，4AP 限度放宽至 1000ppm 或 0.1%w/w，引用了更不敏感的自动 HPLC 方法。我们的产品采用较低的药物含量规格（50ppm，相当于 500mg 对乙酰氨基酚片中含有 25μg 4AP），由于基质干扰，药典 HPLC 测定法在此低水平下不适用。因此，需要一种快速、自动的分析方法。本文提出了一种高度灵敏、精确和自动化的方法，采用流动注射（FI）分析技术定量测定这种降解产物的低水平。将药物含量的溶液或片剂的提取物注入溶剂载体流中，并在线与碱性硝普酸钠试剂合并，形成特定的蓝色衍生物，在 710nm 处分光光度法检测。整个过程都使用标准 HPLC 设备。该程序是完全定量的，并使用多元实验设计（多级“中心复合”响应面）模型进行了优化，以提高灵敏度和稳健性。该方法已得到充分验证，线性范围可达 0.01μg/ml。该方法应适用于一系列对乙酰氨基酚产品。
