Nonideal gas corrections for retention and plate height in gas chromatography

Formation of Retention Times

“…A [36,[43][44][45][46][47] if the quantities t 0 ¼ 1/v ¼ dt/dz and t 0 g ¼ 1=u ¼ dt g =dz were used instead of, respectively, 1/v, 1/u. The root cause for the advantage of this approach comes from the fact that, in chromatography, all solutes travel through the same distancecolumn length, L,before their elution, but it takes different time for each solute to make that trip.…”

Averaging the pressure and flow rate of the carrier gas in a gas chromatographic column

“…dx : -C .pdp (8) Since p =Pi at the column inlet (x = 0) and p =Po at the column outlet (x = L, the column length), relation (5) can be presented as…”

“…Thus, by using (13), we can easily calculate the gas pressure Px averaged over the column length, where it drops from Pi to Po in accordance with (8). We insert p for f(x) and (8) for dx:…”

“…In order to calculate the flow rate Fx averaged over the column length, we express the varying F from (9) F-Fop~ (16) P and insert (8) for dx in (13):…”

“…For traditional gas chromatography, i.e., at moderate pressures and pressure drops and Pi >Po, it is common to apply the "classical" factor j 23 , without appreciating the specificity of the different compressibility correction factors outlined above. Equations that incorporate ]'2 and even j4 have been suggested for chromatography with a non-ideal carrier gas, especially at elevated pressurs and flow rates [8,9]. It is remarkable, that all the compressibility correction factors approach unity on reducing the pressure drop in the column to zero, i.e., at pi/Po --~ 1 or, which is the same, at Pi-Po = Ap---> 0.…”