This application note demonstrates the effects of solvent and analyte polarity as they relate to distorted peak profiles as well as offer general recommendations.
We have found that, in general, non-polar injection solvents should be used with Trefoil Columns. Heptane and heptane/IPA mixtures have been shown to be effective at mitigating peak distortion with compounds of various polarity. An interesting trend between analyte cLog P and injection solvent properties has been observed by examining the resultant peak distortion when these are varied. When cLog P is greater than ~2.5 and less than ~4.3 (praziquantel and econazole, respectively), the injection solvent polarity has little effect on the peak shape observed. The compounds tested required a significant amount of co-solvent to achieve reasonable retention, which should attenuate the strong solvent effect. To date, retention and resolution on chiral stationary phases is still unpredictable, which is why the use of broad spectrum chiral selectivity from coated chiral phases is recommended. The polar nature of the polysaccharide coatings and analyte-stationary phase interactions dictate the sample solvents of choice, just as in achiral separations. In all cases, the distorted peak profiles were not the result of mass overloading, evident by comparing injections between different solvents, but of the same mass load. The distorted peaks are caused by a mismatch between the injection solvent and mobile phase polarities. Distorted peak profiles are surprisingly reproducible, exemplified by the growing distorted peak shapes of guaifenesin dissolved in methanol and IPA. However, some distorted peak profiles can be difficult to predict and interpret without both higher and lower injection volumes, as seen with terfenadine dissolved in methanol. When performing analytical chiral separations, the practitioner should take care to examine the polarity of the analyte and stationary phase. By following the sample outline here: use non-polar injection solvents with polysaccharide chiral phases; one can avoid significant peak distortion in chiral separations.