Step-gradient chromatography

Figure 13.7 Selectivity effected by employing different step gradients in the coupled-column RPLC analysis of a surface water containing 0.40 p-g 1 bentazone, by using direct sample injection (2.00 ml). Clean-up volumes, (a), (c) and (d) 4.65 ml of M-1, and (b) 3.75 ml of M-1 transfer volumes, (a), (c) and (d), 0.50 ml of M-1, and (b), 0.40 ml of M-1. The displayed cliromatograms start after clean-up on the first column. Reprinted from Journal of Chromatography, A 644, E. A. Hogendoom et al, Coupled-column reversed-phase liquid chromatography-UV analyser for the determination of polar pesticides in water , pp. 307-314, copyright 1993, with permission from Elsevier Science.

Piepponen TP, Skujins A. 2001. Rapid and sensitive step gradient assays of glutamate, glycine, taurine and y-amino-butyric acid by high-performance liquid chromatography-fluorescence detection with o-phthalaldehyde-mercap-toethanol derivatization with emphasis on microdialysis samples. J Chromatogr B 757 277-283. 

Vidal, S. et al., Fractionation of grape anthocyanin classes using multilayer coil countercurrent chromatography with step gradient elution. J. Agric. Food Chem. 52, 713, 2004. 

Fig.4.4. Reversed-phase chromatography of sixteen PTH-amino acids. Column 37-50 jim Corasil-C, 100 cm X 2 mm I.D. Stepped gradient from water-acetonitrile-isopropanol 100 1.5 1 to 15 1.5 1. Change is marked by an arrow. Flow-rate, 1.2—1.0 ml/min injected volume, 6 Ml- (From ref. 4 with permission of Pergamon Press, Elmsford, N.Y.)...

The SFE can also be used for extractions. Reverse-phase cartridges are available that, after activation with methanol, can be used to remove nonpolar materials from solution. This is true chromatography, not filtration. The adhering material can be eluted in step-gradient fashion with increasing nonpolar solvent fractions. Although they do not have the efficiency of an HPLC... 

Lamb, J. D. and Smith, R. G. (1994) Use of Step Gradients on Different Polymetric Substrates in the Separation of Anions by Macrocycle-based Ion Chromatography, J. Chromatogr. A 671, 89-94. 

Preparative liquid chromatography (in opposition to analytical chromatography) introduces specific requirements, which are mostly related to the separation selectivity and the loadability of a solid phase rather than the separation efficiency or peak resolution. While analytical chromatography separations may use complex profiles of elution gradients, in most of the cases, preparative chromatography utilizes linear or step gradients or a combination of both. 

Investigate the advantages and disadvantages of possible modes of chromatography (e.g. LstK-ratic. gradient, step gradient, displacement, simulated moving bed). 

---