Chromatographic HILIC indexes to characterize the lipophilicity of zwitterions.

Reverse phase high pressure liquid chromatography (RP-HPLC) is widely employed in drug discovery for lipophilicity measurements. Hydrophilic interaction liquid chromatography (HILIC) may represent a good alternative to RP-HPLC in the determination of the lipophilicity of hydrophilic compounds like zwitterions. In this paper three different HILIC stationary phases (ZIC®-HILIC, ZIC®-pHILIC and ZIC®-cHILIC) and two different mobile phases (80%ACN/20%buffer and 90%ACN/10%buffer) were combined to set-up six chromatographic systems. A computational tool named Block Relevance (BR) analysis was firstly used to deconvolute the balance of intermolecular forces governing retention in the six systems. Then the lipophilicity profiles (log k vs pH) of ten model ampholytes were determined. Results support that the lipophilicity of zwitterions at any pH can be successfully determined with a ZIC®-cHILIC stationary phase and an 80%ACN/20%buffer mobile phase. To extend the dataset and confirm results, a second series of zwitterionic drugs was also analyzed.