Simultaneous ion-pair and partition liquid chromatography of acetaminophen, theophylline and salicylate with application to 500 toxicologic specimens.

Acetaminophen (A), salicylate (S), and theophylline (T) are three common pharmaceutical agents involved in drug overdose for which determinations of serum drug concentrations play a pivotal role in clinical management. All three must be included in overdose screening, but often separate methods must be used. By combining reverse phase high performance liquid chromatography (HPLC) for A and T with ion-pair techniques for S, all three drugs can be chromatographed and quantitated simultaneously. A water-soluble ion-pair of S and 2-amino-2-(hydroxy-methyl)-1,3-propanediol eluted in a mobile phase of 4% acetonitrile and 12% acetic acid in water. Relative retention times for A, T and S were 0.41, 0.57 and 1.75 with an internal standard of 8-chlorotheophylline. Validation studies demonstrated recoveries of 88-104%, intraasay precisions of 2.1-6.6%, interassay precision of 3.8-8.0%, detection limits and linearity ranges of 2-200 mg/l for A and T and 10-1,000 for S. Seventy-two drugs were tested for interference. Accuracy studies showed no significant biases when compared to other methods. The method is convenient for toxicologic screening or therapeutic drug monitoring. In 576 consecutive serum specimens submitted for general toxicologic screening, 7.3% were positive for A, 5.2% for S, and 1.7% for T. Only 1.7% had critical concentrations indicating intoxication.