Selection of mobile phase in high-performance liquid chromatographic determination for medicines

A convenient method was developed to select mobile phase to separate drugs commonly used in clinical therapy, using high-performance liquid chromatography (HPLC). The separation conditions determined by this method were similar for each compound. Two kinds of mobile phase, a mixture of acetonitrile-phosphate buffers, pH 4.2 and 2.5, was used and the composition of mobile phase used for a drug in HPLC analysis was systematically determined as follows: (1) the retention time of a drug was measured under the gradient condition, (2) this retention time value was applied to the regression equation which was determined from the retention time values of p-hydroxybenzoate derivatives under the gradient condition and the concentration of acetonitrile in mobile phase, giving about 5 min of retention time, (3) percentage of acetonitrile in the isocratic condition was calculated from this regression equation and a target drug was eluted with the mobile phase consisting of the calculated concentration of acetonitrile. According to the proposed method, the composition of mobile phase, with which retention time value was between 4 to 8 min in the isocratic condition, was examined for 75 drugs clinically used. Seventy-two of the 75 drugs were analyzed well in the mobile phase, their composition was calculated by the regression equation, and the peak shape of each compound was observed to be sharp. Using this method, the time required for not only the setting of HPLC conditions but also the analysis will be shortened.