RAPID ANALYSIS OF ANTIBIOTIC-CONTAINING MIXTURES FROM FERMENTATION BROTHS BY USING LIQUID-CHROMATOGRAPHY ELECTROSPRAY IONIZATION-MASS SPECTROMETRY AND MATRIX-ASSISTED LASER-DESORPTION IONIZATION-TIME-OF-FLIGHT-MASS SPECTROMETRY

A crucial step in the isolation of antibiotic substances is establishi ng whether or not the isolated material represents a new chemical enti ty. Because of the importance of molecular weight to this process-know n as dereplication-mass spectrometry has traditionally played an activ e role. In this communication a strategy for utilizing liquid chromato graphy-mass spectrometry (LC/MS) for novelty assessment is described. Crude extracts (20-50 mu g) are chromatographed by conventional bore h igh-performance liquid chromatography (1 mL/min) after which a postcol umn split to divert roughly one-tenth of the sample to the mass spectr ometer for molecular weight determination by electrospray ionization ( ESI) mass spectrometry. The majority of the effluent is sent to a UV d etector and ultimately collected as 1-min fractions for biological tes ting. As a secondary confirmation of molecular weight, an aliquot of e ach fraction (< 5%) is taken for analysis by matrix-assisted laser des orption ionization (MALDI). The improved efficiency of this approach o ver more traditional schemes utilizing off-line fraction collection an d conventional ionization methods can be explained by several factors. First, the superior sensitivity of ESI and MALDI means that less mate rial is required for successful analysis. Second, on-line LC/MS optimi zes the efficiency of sample transfer and saves both time and labor. F urthermore, the concentration dependence of ESI allows a majority of t he material injected for LC/MS to be recovered for biological testing without compromising the signal available for molecular weight determi nation. As a validation of the above method, crude extracts containing two well-characterized antibiotics-teicoplanin and phenelfamycin-were examined. Results from these analyses are presented along with data f rom the analysis of a potent unknown antifungal sample. (C) 1996 Ameri can Society for Mass Spectrometry.