DIRECT SAMPLE INJECTION INTO THE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC COLUMN IN THEOPHYLLINE MONITORING

A small diatomaceous earth column was used for direct sample injection into a high-performance liquid chromatographic (HPLC) column for theophylline monitoring. The original design of this device has been improved so as to make it easily usable and disposable following use. It consists of a diatomaceous earth-packed polystyrene tube, the inner surface of which is coated with PTFE, having a capacity of ca. 5 μl of plasma or serum sample, and a stainless-steel needle for introducing an extract into the HPLC sample injector. Using this device together with an optimized injection solvent mixture, an accurate determination of theophylline can be carried out at low cost. The results obtained were comparable to those given by an immunological method, such as fluorescence polarization immunoassay. © 1990.