Tubing modifications for countercurrent chromatography: Investigation of geometrical parameters

ABSTRACT

Countercurrent chromatography (CCC) is a separation technique which may be described as a combination of a great number of liquid–liquid distributions of analytes in a two-phase solvent system with liquid chromatography (LC) features. Even optimized CCC separations currently provide a lower number of theoretical plates when compared to LC. For this reason, instrumental advancements are indispensable to, at least partly, overcome this drawback. Recently, we found that improvement of the classic CCC coil, that is using a long hollow tubing, may be achieved by the introduction of tubing crimpings which increase the stationary phase retention. In this study, we systematically investigated the effects of three geometrical parameters (crimping depth, distance between two crimpings as well as partial or complete crimping of the tubing) on the stationary phase retention by a factorial design of experiments approach. Separation efficiency tests were performed with two groups of analytes: fatty acid methyl esters (FAME) in the n-hexane/acetonitrile (HAcn) and alkyl p-hydroxybenzoates in the n-hexane/tert-butylmethylether/methanol/water solvent system. The most narrow crimping distance and the deepest crimping of the tubing were the best configurations in the examined flow rate range.

GRAPHICAL ABSTRACT

KEYWORDS:

• Countercurrent chromatography
• instrumentation
• separation efficiency
• stationary phase retention
• tubing modification

Acknowledgments

We are grateful to the state of Baden-Württemberg for providing a stipend grant to Michael Englert. The authors owe a debt of gratitude to the Machine Instrumentation Facility of the University of Hohenheim for their help in the fabrication of the crimping tool.