The gas-liquid chromatographic estimation of phenacetin and paracetamol in plasma and urine

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Abstract
Methods are described for the gas-liquid chromatographic estimation of phenacetin and paracetamol in plasma and free and conjugated paracetamol in urine. p-Chloracetanilide and p-bromacetanilide were used as internal standards. The drugs were extracted with ethyl acetate and before chromatography were converted to trimethylsilyl derivatives with N,O-bis(trimethylsilyl)acetamide (simultaneous assay of phenacetin and free paracetamol in plasma), or N-trimethylsilylimidazole (assay of paracetamol alone). Phenacetin was extracted with chloroform and chromatographed directly. Paracetamol glucuronide and sulphate were hydrolysed enzymatically to the parent compound before extraction. Recovery of added phenacetin and paracetamol in plasma at concentrations of 1–100 μg/ml was complete, and the limit of detection of the drugs in plasma was 0.05 μg/ml.