Effect of the eluent pH and acidic modifiers in high-performance liquid chromatography retention of basic analytes

Selection of suitable stationary phases and optimum conditions for their application in the separation of basic compounds by reversed‐phase HPLC

“…It is possible that extensive hydration of the protonated base gives rise to size exclusion effects and that these hydrated ions are not effectively desolvated in formic acid. Poor desolvation can be described in terms of the poor "Hofmeister Series" effect of these ions [32,33]. Put in a different way, the low ionic strength of these solutions compared with phosphate buffers may give much lower "salting out" effects; such effects have been known and utilised for many years in the purification of proteins and in hydrophobic interaction chromatography separations of proteins.…”

Reversed‐Phase HPLC

“…The opposite scenario for retention dependence versus pH is observed for basic compounds (Figure 4-21) [56]. In the mixture of basic components shown in Figure 4-21 (pyridinal species), increasing the pH of the aqueous portion of the mobile phase from 1.5 to 9 led to the enhancement of the retention of the basic analytes.…”

Optimization of the separation conditions of tetracyclines on a preselected reversed-phase column with embedded urea group

“…The obtained difference in the desolvation could be attributed to the charge density in which this charge is more delocalized in perchlorate than in citrate and dihydrogenophosphate ions. This phenomenon is called chaotropic effect [46]. On the other hand, all the analytes show an increase of their retention time with increase of the phosphate buffer concentration in the mobile phase at pH 2.5 (Fig.…”