The use of a particle beam (PB) Interface for quantitation by Isotope dilution LC/MS was Investigated. Coelution of singlelabeled Internal standards (IS) with native compounds caused enhancement of the IS signal. The magnitude of enhancement for [3-13Ci]caffelne was affected by several experimental parameters, but no differences were observed In the 12C/13C response ratios under these conditions or upon analyte Introduction via a gas chromatography (GC) Interface. No coelution enhancement was observed with [ 1,3,7-13C3]caffelne, demonstrating that mass transfer effects and chemical complex formation do not affect PB transmission efficiency. Spectral overlap between native analyte and IS peaks and nonlinear detector responses cause the observed coelution enhancement. These results confirm that PB/LC/MS does not have Inherent limitations for use In Isotope dilution experiments as they have been performed by GC/MS. An equation was derived that permits accurate calculation of Isotope dilution results using a single-or multiple-labeled IS. Application of this equation could allow expansion of the Isotope dilution technique performed by PB/LC/MS or GC/MS to Include singlelabeled IS compounds without the need for nonlinear regression analysis of calibration curves.
The incubation of Bacillus subtilis W23 or Bacillus cereus on a vancomycin-containing medium resulted in a rapid contraction or shrinkage of the cells which was followed by lysis. The ejection of protoplasm from the cell during lysis was very forceful. The "burst" of protoplasmic material was observed at the ends of the cell and at one or two sites on the lateral cell wall. The results are consistent with the hypothesis that vancomycin inhibits cell wall synthesis and ultimately destroys the normal structure and integrity of the wall.
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