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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.

Golay's theory for open tubular GC columns was recently revised for application to rectangular GC columns. The HETP was found to be the same as for open tubular columns provided the average linear velocity, u, and the resistanceto-mass-transfer-in-the-gas-phase, C , are redefined. In this paper, a simplified M expression for the average linear velocity is derived and used to fit a variety of exit flow data collected on microfabricated rectangular GC columns. Also the resistance-to-mass-transfer-in-the-gas-phase is studied and the results compared to earlier relationships derived by Giddings, Chang, Myers, Davis and Caldwell, and by Golay. The three theories agree, with the present theory predicting a slightly higher value for C for large retention indices. The slightly higher value for C is M M attributed to the geometry for the rectangular column that is better modeled with the present theory than the former theories.

In conclusion, it appears that the correlation discussed above is very helpful to predicting Dv values and obtaining the best separation conditions. ACKNOWLEDGMENTThe author expresses her thanks to H. Hatano, S. Egashira, and S. Rokushika for helpful discussions and suggestions for this work.

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