Theophylline estimation-a comparative evaluation of a gas chromatographic method and a high-performance liquid chromatographic method.

A comparative evaluation of a gas-liquid chromatographic (GLC) assay and a high-performance liquid chromatographic (HPLC) assay for the determination of plasma theophylline levels has been carried out. Both methods are reliable, accurate, and technically simple and appear to be specific for theophylline. The HPLC system is more sensitive (sample volume 25 micrliter) than the GLC system (sample volume 500 microliter) and is therefore suitable for the estimation of theophylline in microsamples. The HPLC system also has better precision (coefficient of variation: within-batch 2.0%, between-batch 3.0%) than the GLC system (coefficient of variation: within-batch 3.5%, between-batch 5.6%). Good correlation (r=0.964) was found between plasma theophylline levels (n=75, observed range 4-186 mumol/l) determined by each procedure. The results of this study indicate that, of the two systems investigated, HPLC is the method of choice.