Kinetic behaviour in supercritical fluid chromatography with modified mobile phase for 5 μm particle size. Part II: Effect of outlet pressure changes

In this second part, we achieved a study on the outlet pressure changes (from 8 to 25 MPa) on the chromatographic efficiency in term of equivalent plate number (H). Moreover, because the temperature changes related to the cooling effect also modify the fluid viscosity, i.e. the pressure drop, a specific, and simple, data treatment on inlet pressure values is applied to correlate non linear variations of the pressure drop to temperature changes along the column. This data treatment seems to describe the temperature changes along the column, without using temperature measurement. Two phenomena are observed, the previously described cooling effect due to CO2 depressurisation, but also a frictional warming effect, such as the one reported in UHPLC with sub-2 μm particles. The combination of these two effects leads to varied and complex efficiency changes depending on the outlet pressure and the flow rates in SFC.