Title:
A chemometric approach to elucidate the parameter impact in the hyphenation of evaporative light scattering detector to supercritical fluid chromatography.

Abstract:
The aim of this work was to elucidate the effects of parameters influencing the evaporative light scattering detector (ELSD) response when it was coupled to supercritical fluid chromatography (SFC). Phthalates, currently used as plasticizers in medical devices, were selected as model compounds. The configuration of the hyphenation setup was firstly optimized and shown that both peak efficiency and sensitivity were improved by connecting the ELSD to the SFC before the back pressure regulator (BPR). By using a tee-junction which splits the flow after the PDA towards the collect fraction (or waste) and the ELSD, this instrument configuration has the advantage to be applicable for small-scale preparative SFC. The impacts of other parameters such as mobile phase composition and flow rate, outlet pressure, column oven temperature and ELSD drift tube temperature on the ELSD signal were evaluated using a chemometric approach. First, it was demonstrated that a classical mobile phase composed of CO2-methanol 90:10 (v/v) was suitable to obtain great nebulization efficiency. The flow rate of the eluent was the second main effect factor. The setting must be as low as possible to avoid the loss of large particle size in the drift tube resulting in a loss of signal intensity. Concerning the outlet pressure, the configuration of the setup between SFC and ELSD requires a setting as high as possible to limit the partial liquid-vapor separation of the mobile phase in the restrictor tube. Finally, due to the low quantity of solvent which must be evaporated in the detector, a drift tube temperature of 25 °C is suitable for the hyphenation of ELSD to SFC. In the optimized conditions, the proposed SFC/ELSD method could be suitable to quantify plasticizers in medical devices.