General description

CLC columns use the copper ligand concept described by Davankov to effect enantiomer separation (1). The method uses a small, chiral bidentate ligand attached to the silica surface and a copper sulphate-containing mobile phase. The copper ions coordinate with the chiral selector on the stationary phase and carboxylic acid functional groups on the analytes to form transient diastereomeric complexes in solution. The technique also has the advantage of giving small acids with no UV chromophore a strong 254 nm signal. CLC columns are ideal for analysis of hydroxy acids, like lactic, malic, tartaric and mandelic acids, amino acids, other amines and bi-functional racemates, like amino alcohols. Proline and aspartic acid are particularly suited for low-level detection on the CLC column since the copper complex is detected at 254 nm UV. Both can be resolved on the CLC-D or CLC-L in 5 mM CuSO₄ with the usual reversal of elution order from the CLC-D to CLC-L. In theory, any analyte that can complete the coordination with the copper ion can be resolved. Two versions of the column provide elution order reversal. On the CLC-D column, the L enantiomer generally elutes before D, with the exception of tartaric acid. The reverse is true on the CLC-L column where D elutes before L. Features: Separates α-hydroxy carboxylic acids, amino acids and other α-bifunctional compounds High selectivity with simple mobile phases Copper complex gives strong UV 254 nm signal Simple reversal of elution order, CLC-L vs. CLC-D Excellent reproducibility(1) Davankov, V. A.; Rogozhin, S. V. Ligand chromatography as a novel method for the investigation of mixed complexes: Stereoselective effects in a-amino acid copper(II) complexes. J. Chrom. A. 1971, 60, 284-312.

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