A rapid and specific high-performance liquid chromatographic assay for theophylline in biological fluids.

A rapid, specific high-performance liquid chromatographic analysis of theophylline in plasma, serum, and saliva is described. Proteins present in the biological samples are precipitated with 6% perchloric acid and the clear supernatant is chromatographed on a reversed-phase column. Only 100 microL of serum is required and concentrations as low as 0.07 micrograms/mL can be measured accurately. Other xanthines do not interfere in the assay. Within- and between-day variation is less than or equal to 2.2%. The method shows less bias and greater precision than the TDx (Abbott Diagnostics) procedure commonly used in clinical laboratories.