Simplified micro-scale procedure for preparing samples for theophylline determination by liquid chromatography.

We describe an improved procedure for the preparation of plasma or serum for determination of theophylline by reverse phase high-performance liquid chromatography. Quantitative results are available in less than 30 min from receipt of sample. The chromatogram is complete in 8 to 16 min, which includes the use of an internal standard. Sample preparation consists of simple solvent denaturation of the sample proteins, and centrifugation to remove protein before chromatography. No precolumn is required to pretect the separating column. No interference was noted when sodium or lithium heparin or ethylenediaminetetraacetate were used as anticoagulants, but citrate treatment proved to be unsatisfactory because of a highly absorbing band that eluted with the same retention volume as theophylline.