Semi-preparative on-line supercritical fluid extraction-supercritical fluid chromatography for solid-state injection and purification

Thanks to the versatility and low viscosity of sub/supercritical fluids, supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC) are attractive to extract and separate molecules in a quick and efficient way. By coupling both techniques, on-line SFE-SFC becomes even more versatile and can extract, separate, and detect molecules in a single approach. When used at semi-preparative (semi-prep.) scale, on-line SFE-SFC can also be an interesting tool to perform solid-state injection and simplify sample pretreatment before purification. The aim of this publication is to examine the possibilities offered by semi-prep. on-line SFE-SFC for solid-state injection and determine the key parameters for method development, using ibuprofen as a case study. First, solubility changes of ibuprofen in a pressurized carbon dioxide (CO₂)/methanol mixture were investigated, revealing a favorable solubility at 20 % of co-solvent. Then, an SFC method was developed at analytical scale and scaled up to semi-prep. SFC. This method allowed the separation of ibuprofen from structurally related compounds in less than 3 min, using a Shim-pack UC PolyVP column and 30 % of MeOH in pressurized CO₂. After that, the effect of co-solvent ratio and extraction duration on semi-prep. on-line SFE-SFC solid-state injection was investigated. With an appropriate static extraction using 20 % of co-solvent for 1 min followed by a dynamic extraction with 5 % of co-solvent over 4 min, it was possible to inject and purify 500 mg of solid-state ibuprofen in 10 min. Finally, the methodology was applied to 2.5 g of sample, demonstrating its suitability for larger solid-state injection.