Separation of theophylline, caffeine and related drugs by normal-phase capillary electrochromatography.

A capillary electrochromatography (CEC) method has been developed for the separation of theophylline, caffeine and five related drugs on a normal-phase column with UV or photodiode array detection. Several binary, ternary and quaternary mobile phase compositions are evaluated for optimal resolution and elution of these drug analytes. The importance of selecting suitable organic solvents, buffer electrolyte, pH and applied voltage is demonstrated by a systematic study. Excellent separation is achieved for the eight drugs using a ternary mobile phase composition of isopropanol/hexane/1 mM Tris (52:40:8, pH 8), with an efficiency of 63000 theoretical plates per meter at room temperature. Detection limits are typically at the low microg/mL level. The developed method is simple to use and it gives acceptable day-to-day reproducibility.

Direct injection HPLC method for the determination of phenylbutazone and oxyphenylbutazone in serum using a semipermeable surface column.

A direct injection HPLC method has been developed for the determination of phenylbutazone and its active metabolite oxyphenylbutazone in serum using a semipermeable surface (SPS) column. The method is easy to perform and requires 20 microliters of a filtered serum sample. The chromatographic time is less than 13 min using a mobile phase of 15:85 v/v acetonitrile-0.05M phosphate buffer pH 7.5. The method was linear in the range 0.5-20 micrograms ml-1 (r > 0.99, n = 6) with R.S.D. less than 6%. Interday and intraday variability were found to be less than 8.3%. The limit of quantitation and detection were 0.5 and 0.25 microgram ml-1 (s/n > 3), respectively, for both drug and metabolite.