ISSN:
1612-1112
Keywords:
Column liquid chromatography
;
Reversed phase
;
Void volume
;
Adsorption isotherms
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Summary In reversed-phase liquid chromatography with n-alkyl bonded silica, the dead volume (V0) of the column is theoretically indeterminate owing to adsorption of organic modifier on n-alkyl chains and of water on silanol groups. With binary mobile phases, retention volumes of the mobile phase components and of their deuterated species are relaeed to the adsorption isotherms and V0 by equations which can be solved with some assumptions on the adsorbed layer composition. Methanol-water and acetonitrile-water systems are studied. As the experimental excess isotherm shows a linear part in the concentration range 50–80% in organic modifier, the hypothesis of an adsorbed layer of constant composition in this range is possible. When increasing the water content of the mobile phase, adsorption of water occurs up to saturation of silanol groups. Then the assumption of a constant water content for a mobile phase having more than 50% of water is applied. With the hypothesis of a constant adsorbed content of organic modifier when the eluent has more than 80% of organic modifier, V0 and the absolute isotherms are calculated over the entire range of mobile phase composition. Experimental retention behavior of the mobile phase components are totally explained by these V0 determinations. The retention times of commonly used V0 markers are compared with V0 values. It is shown that, when buffering the eluent, no visible effect on the distribution equilibrium is observed, so that injection of concentrated potassium nitrate is a convenient method to measure V0. With a few solutes with are UV detectable it is possible to measure V0 whatever the mobile phase composition in methanol-water and acetonitrile-water systems.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02311526
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