Serum quinidine determination: comparison of mass-spectrometric and extraction-fluorescence methods.

A comparison of two analytical methods of quinidine plasma determination--the modified extraction fluorometric method and the mass spectrometric method--was made. Plasma supplies collected at steady state from normal human volunteers participating in a bioavailability study were analyzed, using both methods. A total of 359 samples were analyzed. Comparison of both sets of values, by linear regression, yielded an r2 value of 0.84. The results of this comparison were consistent with the results reported by others, confirming that the commonly used extraction fluorometric method of quinidine determination is sufficiently accurate for monitoring quinidine plasma concentrations in the patient care setting, as well as for bioavailability comparisons between products.