Cromatography process for recovering a substance or a group of substances from a mixture

Method for improving the performance of a preparative batchwise Super Critical Fluid Chromatographic separation for the recovery of a target fatty acid or derivative thereof, or of a group of target fatty acids or of derivatives thereof from a mixture comprising the step of running the mixture through a chromatographic column charged with a stationary phase chosen from the group consisting of aluminium oxide or aluminium oxides, titanium oxide or titanium oxides, silica gel or silica gels, amino propyl modified silica gels, diol modified silica gels, phenyl modified silica gels and “reversed phase” phases where the stationary phase is chosen from the group consisting of octadecyl carbon chain (C18)-bonded silica (RP18), octyl carbon chain (C8)-bonded silica (RP8) and propyl (C3)-bonded silica (RP3), and a mobile phase chosen from the group consisting of ethylene, propane, ammonia, dinitrogen dioxide and CO2, and

• applying a pressure and/or temperature gradient to the chromatographic column during the elution of the target fatty acid or derivative thereof during the running of the said mixture on the chromatographic column, wherein one or both of the target values set for the pressure and/or temperature gradient applied during elution of the target fatty acid or derivative thereof lie outside a supercritical area of the eluent employed.