Analysis of paracetamol using solid-phase extraction, deuterated internal standards, and gas chromatography-mass...

A rapid method for determining paracetamol (acetaminophen) in whole blood and liver tissue samples is described. Blank plus single-point calibration gives reliable quantitation at therapeutic and higher concentrations. Whole blood and liver tissue samples containing a deuterated internal standard were extracted using Bond Elut Certify columns. Butyl derivatives were formed using n-iodobutane and tetramethyl ammonium hydroxide under mild conditions and were extracted into ethyl acetate as a cleanup step. Recovery was better than 90%, and sample preparation time was less than 2 h. Gas chromatograph run time was less than 20 min. SIM of two ion pairs formed by electron impact ionization resulted in intraday coefficients of variation (CV) less than 3.03% (7.48% in liver) and interday CVs less than 8.93% (for midtherapeutic concentrations in whole blood). Linearity was observed from subtherapeutic to high, fatal levels. This method has been applied to forensic cases and has significantly reduced analytical time while improving casework quality. Results of a case study involving paracetamol are given.