methanol in water with 0.2% acetic acid. Snyder solvent strength
plots were generated using five methanol–water–acetic acid mobile
phases: 15%, 20%, 25%, 30%, and 35% methanol in water with 0.2%
acetic acid. (For this study, it was not possible to generate retention
data using methanol–water mobile phases with less than 15% methanol
because of difficulties encountered in eluting each component of the
test mixture from the column.) The six compounds studied exhibited
classical RPLC hydrophobic behavior. Plots of ln k′ versus organic modifier
concentration were linear for each test mixture compound investigated.
Retention time decreases as the concentration of methanol
increases because the stationary phase is saturated with methanol
(i.e., the organic modifier) over the mobile phase composition range
investigated.