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In our previous paper, we introduced a new method for the enantioseparation of cathinones on chiral zwitterion ion exchangers by SFC-ESI-MS with an inverse make-up solvent gradient. The inverse gradient enabled us to stabilize electrospray ionization while simultaneously increasing MS response. In this study, we fine-tuned our previously optimized SFC-ESI-MS method and compared its efficiency with that of the default ESI-MS method. To enhance analyte detection, we designed a complex series of experiments in which all combinations of the following three parameters were evaluated: cone voltage (5 to 27 V), probe temperature (250 to 550°C) and capillary voltage for positive ionization (0.3 to 1.5 kV). After optimization, various ratios of the make-up solvent (methanol/water/formic acid) introduced before entering the ESI ion source were also tested. Despite this comprehensive testing regime, there were no significant differences between the results obtained for the tuned and default ESI-MS parameters. Similarly, the most suitable make-up solvent composition was the originally used ratio of 90/10/0.1 (v/v/v). These results reinforce the findings of our previous paper, in which we optimized the make-up solvent flow rate and showed its significant impact on ESI-MS response.
Paškanová et al. (Wed,) studied this question.