Retention of ionizable compounds on HPLC. 6. pH measurements with the glass electrode in methanol–water mixtures

Influence of stationary phase chemistry and mobile‐phase composition on retention, selectivity, and MS response in hydrophilic interaction chromatography

“…In general, these studies found that mobile phases containing an acid (e.g. formic or acetic) had an actual mobile-phase pH that was closer to neutral as the percentage of organic solvent increased [17]. The same observation was made for mobile phases containing ammonium and butylammonium; however, the pH went from 9 or above back toward neutral for increasing amounts of organic.…”

“…Several reports have been published describing the change in pH with increasing amounts of organic solvent [16][17][18]. In general, these studies found that mobile phases containing an acid (e.g.…”

“…Never-theless, developing HILIC separations based on these theories alone remains somewhat challenging, and it is not as straightforward as RP-HPLC. Further complications arise from the changing mobile-phase pH and analyte pK a values in highly organic solutions [16][17][18].…”

Retention of ionizable compounds on HPLC. Modelling retention in reversed-phase liquid chromatography as a function of pH and solvent composition with methanol-water mobile phases

“…where the quantity 8 stands for the socalled medium effect, and can be easily calculated from the organic modifier content of the mobile phase by empirical equations [2,3]. For methanol:water [3]:…”

“…If the mobile phase SpH or sSpH scales are used in Eqs (1) or (2), the obtained sol lute pK a will correspond to the pK~a in the mobile phase " s i s i (1. e. wPK a or sPK a) [1,2,3]. There are several models reported in the literature that describe the variations of the fitting parameters of Eq.…”