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1. Treatment with trypsin of cells of Staphylococcus aureus strain Cowan I, known to carry a protein component that includes the Jensen protein A, results in an increase in the negative mobility of the cells at pH values greater than 6. 2. Similar treatment of cells of strain Wood 46, which has no surface protein component, causes no change in the electrophoretic mobility. 3. Electrokinetically heterogeneous populations are observed in two strains of S. aureus, one of human and the other of animal origin. Evidence is presented ascribing this to the presence of varying amounts of protein components on the surface of different cells.

1. pH-mobility curves of various laboratory strains of Staphylococcus aureus are non-sigmoid in shape, and all pass through a maximum value in the range pH4-5. 2. The maxima in the curves are not due to incomplete washing of the cells, adsorption of buffer components or irreversible surface damage. 3. Mild oxidation of the cell-surface teichoic acid with sodium metaperiodate gives cells that have typical sigmoid pH-mobility curves, characteristic of either a simple carboxyl surface or a mixed carboxyl-amino surface. 4. The results are discussed in terms of a pH-dependent change in the configuration of the teichoic acid molecules at the surface.

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A highly specific normalphase liquid chromatographic method for the rapid determination of alprazolam In human serum Is reported. By use of a structurally similar trlazolobenzodlazeplne (triazolam) as Internal standard, serum Specimens were buffered with four volumes of 4 M sodium hydroxide and extracted with toluene. The extractlon solvent was evaporated to dryness and the extraction residues were reconstituted In acetone/acetonltrlle (1/5, v/v). The samples were chromatographed on a microparticulate silica column (Zorbax SIL, 25 cm X 4.6 mm 1.d.) using a mobile phase containing acetonitrlle/water (94/6, v/v). Detection at 214 nm allowed quantltation of less than 0.5 ng/mL of this highly potent anxlolytic when analyzing as little as 0.5 mL of serum. Although the method has not been extenslvely validated for trlazolam, it has been used for the quantltatlon of this trlazolobenzodlazeplne over a comparable concentration range. The methodology was used to monltor serum concentration-time profiles In human volunteers foilowing Intravenous admlnlstratlon of alprazolam. Disappearance of alprazolam from systemic circulation was triphasic. The mean terminal disposition half-life calculated by nonlinear estimation (NONLIN) was 15.9 f 6.1 h.Alprazolam (Figure 1, A; 8-chloro-6-phenyl-l-methyl-4H-

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