Estimation and identification in blood plasma of paracetamol (N-acetyl-p-aminophenol) in the presence of barbiturates.

Barbiturates are a source of interference in the estimation of paracetamol by both UV spectrophotometry and gas-liquid chromatography (GLC). Experiments have shown that the interference by barbiturates on GLC can be avoided by benzoylation (in aqueous solution) of the paracetamol. This O-benzoyl derivative can be N-silylated to give an additional identification parameter. The method, which requires ml of sample, will quantitatively and qualitatively estimate "free" paracetamol in plasma and in post mortem blood in the range of 2-40 mug of drug per millilitre of sample.