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A Step in the pH Direction |
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Written by The Clever Chromatographer
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Saturday, 02 January 2010 17:51 |
A recent article in the Journal of Chromatography A reports the separation of six cephalotaxine-type alkaloids (all tertiary amines) with step-pH-gradient HSCCC. I am familiar with step-gradient and pH-zone-refining CCC so naturally I was intrigued by the technique described in the title. “Completed preparative separation of alkaloids from Cephaltaxus fortunine by step-pH-gradient high-speed counter-current chromatography.” JCA 1216 (2009) 4663-4667. The rather unremarkable 1:3:4 mixture of hexane-ethyl acetate-water was equilibrated and separated. The upper organic (stationary) phase was doped with 0.05% trifluoroacetic acid. The lower aqueous (mobile) phase was separated into three portion and each portion was doped with a different eluter – 2% ammonium hydroxide, 0.2% ammonium hydroxide, and 0.01% TFA. After introduction of the stationary phase, the sample was injected. Then the column was eluted with the 2% ammonium hydroxide first, 0.2% ammonium hydroxide second and 0.01% TFA last. Interestingly, the chromatogram has the “square” peaks that are often seen with pH-zone-refining. Another surprising detail is that the order of elution is exactly the same as reversed-phase HPLC column with methanol and aqueous ammonium carbonate elution! The solvent selection method was not reported in great detail. For example, how this elution was different than the same solvent system with no additives
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Last Updated on Saturday, 02 January 2010 17:57 |
