An improved theophylline method by EMIT on the multistat III micro centrifugal analyzer

We describe several modifications of the Syva EMIT assay for theophylline on the Instrumentation Laboratories Multistat III Micro Centrifugal Analyzer (MCA) designed to improve precision. These modifications include increased sample volume, increased time interval for obtaining the delta optical density, the use of buffer with no detergent to prevent the possibility of premix of reagents, and reversal of the order for loading the reagents. Furthermore, the loading of sample and reagents has been programmed to match the concentrations and sample volume/reagent volume ratios recommended by Syva. Precision analysis of the method yielded coefficient of variation values of less than 10% for controls (n = 52) and standards (n = 69). A cross-correlation study comparing the MCA method and the recommended method on the Gilford 3500 yielded a slope of 0.98, a y intercept of 0.07, and a correlation coefficient of 0.992. The method is precise, fast, and inexpensive, costing ¿63 per patient sample for a full rotor.