Role of extra-column volume in the efficiency of high-speed liquid chromatography

doi:10.1016/S0021-9673(01)90424-8

Journal of Chromatography A

Volume 321, 1985, Pages 69-79

https://doi.org/10.1016/S0021-9673(01)90424-8 Get rights and content

Abstract

The role of extra-column contributions to the height equivalent to a theoretical plate, H, in high-speed analysis is pointed out. A simple equation, usually applied to band broadening in the column, was used to demonstrate that extra-column contributions influence not only H but also, to a varying extent, coefficients of the equation. Coefficients C in the equation H  f(u) were determined experimentally with the use of sorbents with particle diameters of 6 and 3.2 μm. Columns 55 and 30 mm long were connected to spectrophotometric and electrochemical detectors, respectively, having detection cell volumes of 20, 10 and 8 μl and 7 nl.

C as a function of the capacity ratio, k, follows the theoretical dependence only when a cell having a volume small enough with respect to the volumetric variance of the peak is used. For the work at higher flow-rates of the mobile phase (important for high-speed analysis), it is necessary to optimize the size of the detection cell. It is shown that under the experimental conditions given, an increase in the detection cell volume leads to an increase in H at the minimum of the dependence on the mobile phase flow-rate, but also, in contrary to expectation, to a decrease in C. As a consequence, at higher flow-rates of the mobile phase, lower values of H are found with the use of a detector with larger detection cell, which makes it possible to increase the speed of the analysis. The detection cell volume also affects the character of the dependence of H on u significantly.

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