Effects of temperature and percentage of organic modifier were studied on retention and selectivity in RP-HPLC using solvation parameter model. The system constants were determined by multiple linear regression analysis from experimental values in the retention factor for a group of different solutes with known descriptors by computer using the program SPSS/PC. The experimental results showed that the variation of percentages of organic modifier (5-20% V/V CH3CN) changes cavity formation (m = +3.55 to +2.53), dipole-dipole interactions (s = +0.62 to −0.64) and hydrogen-bond acidity (b = −2.41 to −3.27) terms. The variation of temperature (5-45°C) also changes cavity formation
(m = +3.21 to +2.56) and dipole-dipole interactions (s = +0.34 to −0.22) terms.