Retention mechanism of the multifunctional solute on columns with different coverage densities using highly aqueous reversed-phase conditions.

A series of 11 homemade octadecyl bonded phases with different coverage densities were tested to determine the influence of the stationary phase on the retention in highly aqueous mobile phases. The concentrations of the organic modifiers (methanol and ACN) were in the range of 0-20%(v/v). The coverage density of bonded ligands and the presence of the end-capping have strong influence on the solute retention. Amoxicillin (AMO) was chosen as the test compound. Dual properties of AMO, which contain hydrophobic skeleton and polar groups (amino, hydroxyl and carbonyl), cause irregular changes of the retention over the stationary phase hydrophobicity and silanol activity at given mobile phase composition. Presented data show that application of non-standard low coverage density C18 phases allow to determine AMO in the RPLC condition with high retention.