This research determined the proportions of lidocaine conformer groups in a supercritical carbon dioxide environment at constant pressures (10, 20 and 30 MPa) and temperatures of 35, 50 and 70 °C for the first time. Results show that the proportions of Cis-conformers and Trans-conformers depend on temperature, with the proportion of Cis-conformers increasing with increasing temperature and the ratio of Trans-conformers increasing with decreasing temperature. Thus, on the 10 MPa isobar, as the temperature increases from 35 °C to 70 °C, the Trans-/Cis-conformers ratio changes from 99.4%/0.6% to 88.9%/11.1%. On the 20 MPa isobar at the same temperatures the conformer distribution changes from 53.3%/46.7% to 95.6%/4.4% and on the 30 MPa isobar the corresponding values are 4.8%/95.2% and 46.5%/53.5%. It is intriguing how the proportions of conformer groups vary with temperature and this knowledge could be beneficial for micronizing different compounds using supercritical fluid technologies.
