Determination of quinidine in human serum in the presence of diuretics

A new method for the determination of quinidine in human serum by fluorometry is described. The interference of triamterene encountered with other methods is greatly reduced, whereas a number of other diuretics do not interfere at all. The specificity is based on quenching of the fluorescence of cinchona alkaloids by chloride ions. The method has good reproducibility and linearity, and gives a recovery of 98%. A serum sample of 0.1 ml is sufficient for the assay. Comparison with two other methods showed that this procedure yields the total amount of cinchona alkaloids present in serum, which makes it extremely useful for routine clinical analysis.