Defining a generic column set for achiral supercritical fluid chromatography applied to pharmaceuticals or natural products

When starting a method development in supercritical fluid chromatography (SFC), the first step is usually to screen several stationary phases based on previous experience or simply based on what is available in the laboratory. However, as there are now a large number of stationary phases available for SFC, the choice of an adequate set of columns to rapidly achieve a satisfying result can be difficult. In this project, 16 columns comprising a wide diversity of stationary phases and polarities ranging from the most po-lar (like bare silica gel) to the least polar (like octadecylbonded-silica) were compared, based on the gradient analysis of 129 probe compounds. The set mostly comprised active pharmaceutical ingredients, natural products and a few metabolites. The columns were ranked with the help of Derringer desirabil-ity functions taking account of (i) the number of compounds eluted from the column, (ii) the elution time in a suitable time frame, (iii) the average peak width, (iv) the average peak symmetry and (v) the spreading of retention along the gradient time. The five criteria selected showed no correlation. Over-all, it appeared that those columns that had a high overall score were good for several reasons, like bare silica gel, propanediol-bonded silica or pentabromobenzyloxy-bonded silica. Initially, the columns had been screened with a gradient elution starting from 5% co-solvent and ending with 50% co-solvent in CO2. However, for some most retentive columns like amide-bonded silica, too many compounds re-mained non-eluted from the column. To examine this column more fairly, a second elution gradient was applied that ended with 100% co-solvent. This proved effective in restoring good overall performance through the elution of the most polar compounds.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

When starting method development in SFC, the choice of suitable stationary phases can be difficult due to the large number of options available. In this project, 16 columns with diverse stationary phases and polarities were compared to determine their performance. The ranking was based on multiple criteria including the number of eluted compounds, elution time, peak width, peak symmetry, and retention along the gradient time. Columns with high overall scores, such as bare silica gel, propanediol-bonded silica, and pentabromobenzyloxy-bonded silica, were found to be advantageous.