Mobile phase effects in reversed-phase chromatography. VII. Dependence of retention on mobile phase composition and...

The relationship between logarithmic retention factor, kappa, in reversed-phase chromatography and operating conditions including mobile phase composition and column temperature is still controversial. Earlier, the following analytical relationship was proposed for use with alkyl benzenes: kappa = A1 phi (1 - Tc/T) + A2/T + A3 where phi is volume fraction organic co-solvent of the hydro-organic mobile phase, T is absolute temperature and A1-A3 are parameters appropriate to the eluite and stationary phase. Insofar as its use had not been tested with polar eluites that are retained by only one mechanism, its description of the retention of 54 polar and apolar eluites was examined and compared to equations with other, usually more complex, relationships between retention and operating conditions. The following four-parameter equation described best most data: kappa = A1 phi (1 - Tc/T) + A2/T + A3 + A4 phi. But neither this nor any other four-parameter equation under examination here emerged solely as the best expression for the dependence of retention on the eluent composition and temperature. The average relative errors were 7.8% and 6% with use of the three- and the four-parameter equations which were found to be best for a given eluite, respectively. In view of the small decrease in error but significant increase in complexity and in data points with the use of the four-parameter equation, the three-parameter equation is recommended for general use.