Thermodynamic Parameters for Predicting Retention of Metronidazole, Efavirenz, and Nevirapine on a GC Capillary Column: Comparison of van’t Hoff–Glew and Clark with Density Functional Theory Calculated Results
摘要
Thermodynamic properties, the change in enthalpy and entropy, for analyte distribution between the mobile and stationary phase during gas chromatography separation of efavirenz, nevirapine, and metronidazole were experimentally determined. Calculations were based on data obtained by isothermal separation of the three compounds over a temperature range of 433.15–463.15 K on a GC column stationary phase. Two thermodynamic models, i.e., the Clarke and Glew theory based on the integrated van’t Hoff equation and the Castells model were used to calculate the changes in enthalpy and entropy. The values obtained from the two models were compared with those obtained by density functional theory calculations. Using the van’t Hoff model, the change in entropy for efavirenz was − 79.3 ± 3.4 JK−1 mol−1 and − 71.5 ± 2.1 JK−1 mol−1 using the Castells model, while it was − 65.7 ± 11.6 JK−1 mol−1 using DFT calculations. This trend was observed for nevirapine and metronidazole across the temperature range studied. Error analysis revealed that the temperature range used in making van’t Hoff model estimates violated the requirement espoused by Clarke and Glew, i.e., that application of the integrated van’t Hoff equation was only applicable over a narrow temperature range of 10 K. The Castells model values compared well with DFT values and were upheld for retention time predictions. The James–Martin compressibility factor was independent of temperature due to no change in the viscosity of the helium carrier gas over the range studied. It changed with inlet to outlet pressure ratio, which was dependent on the helium carrier gas flow rate.