Thesis (M.Sc.)--Chulalongkorn University, 1995

The effects resulting from differences between sample solvent and mobile phase composition on chromatographic behavior of paracetamol, phenol, methylparaben, ethylparaben and propylparaben at 20° to 35℃ on reversed-phase high-performance liquid chromatography were investigated. Two columns used in this study were LiChrosorb RP-8 (10 µm, 4.6 mm I.D. x 25 cm.) and LiChrosorb RP-18 (10 µm, 4.6 mm I.D. x 25 cm.) with methanol/water (60:40, v/v) as mobile phase. The number of theoretical plates (N) for the studied compounds increased as the % (v/v) water in dissolving solvent increased and reached maximum value after 40% (v/v) water concentration. The effect of sample solvent strength was enhanced at higher temperature. At O to 40 % (v/v) water in dissolving solvent, the number of theoretical plates varied with the solvent polarity index(Pi) as a second-degree polynomial function, i.e., N = A0+A1Pi+A2Pi2 at all temperature studied. The retention time of each compound was not affected by the solvent strength. The proposed mechanisms of peak distortion and peak compression occurring from this effect are discussed.