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the resolution. The effect varied with the types of analyte and CD in the run buffer, but the bottom line is that more enantioseparations were enhanced than hindered. Both pH and the presence of potassium ions were found to affect the enantioseparations obtained with the CD/18crown-6 system. Chiral recognition was found to increase Equilibria involved in the formation of the "three-body" with increasing acidity, and complex. (Adapted with permission. Copyright 1998 decrease with increasing potas- Elsevier.) sium. The observed enantioseauthors believe that the complex is not lectivity is explained in terms of a "threestatic, and they propose a series of equilibria body" complex—the analyte + CD ++8reactions to explain the dynamic system. crown-6. The exact structure of this three(J. Chromatogr., A 1998, 793, 115-34) body complex, however, is not certain. The
Combinatorial MIP The combinatorial chemistry approach screens thousands of chemicals against a particular target. Why not make the target a molecularly imprinted polymer (MIP)? Olof Ramstrom and colleagues at Lund University (Sweden) tested the concept by using MIPs to screen a chemical combinatorial library. The library studied in this case is composed of 12 closely related A4androsten-3-one structures. Two of the
library compounds were selected as targets and used to prepare MIPs, which were subsequently packed into an HPLC column. When the entire library was run through the column, the MIPs clearly retained their respective target analytes. The authors believe that this approach can be used to run initial screens against poorly characterized receptors or against receptors that have proven to be difficult to purify. (Anal. Commun. 1198, 35, 9-11)
SPE(edy) analysis of pharmaceuticals In pharmaceutical analysis, manual sample preparation can often cause a bottleneck in LC/MS analysis. Danlin Wu and co-workers at Sanofi Pharmaceuticals, Packard Instrument Company, and 3M have developed and evaluated an off-line solid-phase extraction (SPE) method in a 96-well format that can be performed by robots. The setup was demonstrated with the analysis of three pharmaceutical products. Because of the dense packing in the SPE disk, clogging was a concern wiih biological samples. Dilution provided a way around this problem. In the dilution range 0-23%, the flow rate increased by 10%, but beyond that point no further increases were observed. The mass recovery of the molecule used as the model was independent of buffer dilution. Because the disk SPE provided elution volumee s
