Height Equivalent to a Theoretical Plate Theory for Rectangular GC Columns

Abstract

The theory for the height equivalent to a theoretical plate (HETP) of a miniature rectangular gas chromatographic (GC) column is developed in analogy to Golay's theory for an open tubular GC column. The HETP is similar to that for an open tubular column except for the nonequilibrium or mass-transfer term. Unlike prior theories, the nonequilibrium or mass-transfer term is complexly related to column geometry. The theory successfully predicts the performance of fast chromatography, in the form of both short microbore and micromachined columns. For a given column length, rectangular columns have lower HETPs than conventional capillary columns and higher volumetric flow rates. A good rule of thumb is that the resolution can be adjusted by selecting the column height (provided it is much less than the column width), and the volumetric flow of carrier gas can be adjusted by selecting the column width (or cross-sectional area). A satisfactory compromise is to use a low inlet pressure that also provides an HETP that remains nearly constant over a range of pressures.