Phenols as internal standards in reversed-phase high-performance liquid chromatography in pharmaceutical analysis

To find a series of compounds for use as internal standards in reversed-phase high-performance liquid chromatography, about 70 commercially available phenols were chromatographed under various conditions. The stationary phases used were hydrocarbon chemically bonded silica gels (phenyl, C8 and C18 columns). The mobile phases consisted of 10-60% aqueous-organic solutions (organic solvents, methanol, acetonitrile, tetrahydrofuran and mixtures thereof; aqueous phases, water, buffer solutions of pH 2 and 7, 20 mM sodium sulphate or water containing 5 mM of counter ion). A series of 30 phenol derivatives showed a constant order of elution regardless of the separation conditions and are useful as potential internal standards.