Sensitive high-performance liquid chromatographic determination of EM523, a new erythromycin derivative, in human plasma and urine with ultraviolet detection using column switching.

A sensitive high-performance liquid chromatographic (HPLC) method using column switching is described for the determination of EM523 (I), a new erythromycin derivative, in human plasma and urine. The analyte was extracted from alkalinized plasma or urine with a mixture of n-hexane and acetone. After the evaporation of the organic layer, the reconstituted residue was injected into the HPLC system and separated on the first column. After column switching, the heart-cut fraction contamination the analyte was further separated on the second column and monitored by ultraviolet absorbance at 210 nm. The detection limits were 1 ng/ml in plasma and 10 ng/ml in urine. The method was applied to the clinical trials of I.