Determination of sulfadiazine and N4-acetylsulfadiazine in biological fluids by liquid chromatography on silica gel with an aqueous buffer as mobile phase.

Sulfadiazine and N4-acetylsulfadiazine were determined in biological fluids by the direct injection (plasma after protein precipitation and urine after dilution 100 times) of 20 microliters on a silica gel column. The mobile phase was an aqueous citrate buffer (pH 4.0) and UV detection was a 264 nm. Chromatographic selectivity was optimized by the silica gel surface and pH of the mobile phase. Detection limits were approximately 0.4 microgram/ml for sulfadiazine in plasma and approximately 5 and 7 micrograms/ml of sulfadiazine and N4-acetylsulfadiazine in urine, respectively. In quantitations by peak heights relative to an internal standard (sulfamerazine), within-run precisions (srel%) for sulfadiazine were 1.7 and 4.0% at 40 and 2 micrograms/ml, respectively, in plasma and 0.76 and 1.7% and 25 micrograms/ml, respectively, in urine.