Vancomycin buffer

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

Fig. 2-15. Reversed-phase retention of the first eluted and the second eluted enantiomers of 5-methyl-5-phenylhydantoin as a function of mobile phase composition. The column was a 250 x 4.6 mm vancomycin CSR The buffer was triethylammonium acetate at pH 7.0. The flow rate was 1.0 mL min-1 at ambient temperature (23 °C).

Figure 2.18 Fourier transform infrared spectrum of sol-gel film composed of three layers and containing 10% vancomycin after 14 days of immersion in phosphate-buffered saline (weight measurements and release study showed 90% weight loss and 80% release). Intense silica bands and the bands associated with vancomycin (centred at 1660,1500 and 1397 cm-1) suggest the presence of a sol-gel film with vancomycin that remains after 14 days of immersion. (Reproduced from ref. 13, with permission.)...

NaCNBH3 (10 mM) in phosphate buffer (pH = 3). The slurry is sonicated for 1 h, centrifuged, and the cyanoborohydride solution eliminated. The modified silica is washed with water and methanol, and then dried. This chemistry of binding provided for vancomycin a substantial bonding density of 120 p,mol/g (0.40 p,mol/m ) [70] (see Table 2.2). Surface coverage data for ristocetin A [75] and glycopeptide MDL 63,246 [43,44] were not provided by the authors. 

Fig. 3 ACE/MS of a synthetic all-D, Fmoc-DDXX library of 100 tetrapeptides using vancomycin as the receptor. (A-D) Selected ion electropherograms for the masses indicated (E) reconstructed ion electropherograms for runs without (left) and with (right) vancomycin in the electrophoresis buffer. See text for conditions and further explanations. (Reprinted with permission from Ref. 38. Copyright 1995 American Chemical Society.)...

The problems associated with the basidty of fluoride are underscored by another example taken from Boger s synthesis of the Vancomycin CD and DE ring systems [Scheme 4,51],80 Attempted removal of the TBS group from 51.1 was accompanied by retro-aldolisation of the resultant p-hydroxyphenylalanine subunit to give 513 in 61% yield. Here again, buffering the reaction mixture with acetic acid suppressed the unwanted side reaction and gave the desired deprotected product 513 in 60% yield. 

Under reversed-phase elution conditions, the nature of organic modiher has a very important role on the separation. Thus, methanol proved to provide better enantioselectivity than acetonitrile for the separation of ergotamine on a vancomycin and teicoplanin stationary phase [129]. The buffer concentration also has an influence on the retention of the enantiomeric analytes. An increase in buffer concentration produces a decrease in the retention of the two enantiomers. It was found that in some cases the two stationary phases, teicoplanin and vancomycin, are complementary for a poor separation on vancomycin, the stationary phase produced a baseline separation on teicoplanin and vice versa [129]. 

If vancomycin is needed in a topical form to treat an eye infection, a highly concentrated solution intended for intravenous injection can be diluted. Because this concentrated solution is acidic, dilution with artificial tears or a buffer increases patient comfort. 

Figure 13.9. Affinity capillary electrophoresis-UV-raass spectrometry of a 100-tetrapep-tide library screened for binding to vancomycin (104 fxM in the electrophoresis buffer), (a) The elution of peptides was monitored with UV absorbance during capillary electrophoresis, and the elution time irrieased with increasing affinity for vancomycin. (b) Positive ion electrospray mass spectrum with CID of the Tris adduct of the proton-ated peptide detected at —5 min in the electropherogram shown in a (Reproduced from Ref 52 by permission of the American Chemical ardety.)...

Phenoxypropionic acid, dichloroprop, fenoxaprop, fluaziprop, haloxyfop, and — 75 mM Britton-Robinson buffer with 6 mM Vancomycin — [19]... 

Phenoxy acid — 0.1 M phosphate buffer, pH 6 with Vancomycin [24]... 

Capillary approaches have been shown to be useful for many chiral separations as well as achiral separations. For chiral separations, separation buffer additives containing chirogenic centers (tecoplainin, erythromycin, vancomycin, or cyclodextrans) have facilitated the resolution of enantiomers [26,30,31]. Chiral capillary separations could readily be combined with mass spectrometry because the volume of effluent moving from the separation capillary to the ion source is small and makeup solvent is commonly added by means of an union to stabilize the ion beam. Chiral capillary separations provide an attractive alternative to analytical-scale normal-phase separations when using atmospheric pressure ion-ization mass spectrometry. 

Using this approach, vancomycin was first run in the electrophoresis buffer with a probe ligand, Fmoc-Gly-D-Ala-D-Ala (L), that showed high binding affinity for the target substrate, vancomycin. It was shown that the concentration of vancomycin affected the electrophoretic mobility of L (Fig. 

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