Model describing the role of the pressure gradient on efficiency and speed of analysis in capillary gas chromatography

Neglecting the term describing resistance to mass transfer in the stationary phase, the Golay plate height equation is rearranged in terms of the dimensionless parameters ξ = H/Hmin and ν = uūopt. In the resulting model, two boundary cases can be distinguished: P ≈ 1 and P ≫ 1, P being the ratio of column inlet to column outlet pressure. The two expressions provide a clear insight in the increase in plate height which results from the use of average linear carrier gas velocities other than uopt. Hence the model is very helpful for optimization of the speed of analysis.

The validity of both boundary expressions was checked by comparing them with experimental plate height data. The data under conditions of P ≫ 1 were obtained on a 60 m × 0.4 mm I.D. capillary column directly coupled to the ion source of a mass spectrometer, and on a 10 m x 55 μm I.D. capillary column operated at increased inlet pressure, using atmospheric outlet pressure. A 30 m × 0.4 mm I.D. column was tested using a flame ionization detector, with P ≈ 1.

Excellent agreement was observed between the theoretical prediction and the experimental results.