RESUMO
Often high-performance liquid chromatography method development is done by choosing a single C18 column and optimizing only the mobile phase composition. In this paper, it is demonstrated how to evaluate and optimize the best combination of the different stationary phase chemistries and mobile phases for a limited method development activity. By using column and mobile phase switching, it is possible to automate most of the activity in a nine-step process. Columns are chosen to represent the range of selectivity currently available. Interestingly, although the most popular column is the C18 phase, it is not the best column for the optimized methods in the cases studied.
RESUMO
The phenomenon of aqueous mobile phase induced retention time loss, which has also been referred to as phase-collapse behavior, is investigated using a variety of stationary phases with an aqueous mobile phase. The loss of retention of several water-soluble B vitamins is measured as a function of silica pore size, bonded-phase chemistry, and bonded stationary phase density. It is found that these variables influence the magnitude of the retention time loss behavior and that controlling/optimizing these variables can result in a stationary phase with sufficient retention of the analyte without the column exhibiting the so-called phase-collapse behavior.
RESUMO
The use of unbonded silica as a stationary phase in reversed-phase HPLC is described as a useful alternative to bonded phase columns for polar, lipophilic amines. Using four lipophilic amines, the role of temperature is shown to favorably impact both efficiency and selectivity, which is not universally seen when using bonded phases. As temperature is raised, retention drops on the silica column. The temperature behavior appears to support the hypothesis that retention is dependant upon electrostatic and adsorptive forces.
