A Kinetex EVO C18 column (5 µm particle size, 2.1 mm i.d. × 30 mm) connected to a guard column of the same i.d. was used. This column is said to be stable with 100% water and in a pH range of 1 to 12, suitable for this work. A short column with relatively large particles was opted so that retention times of long-chain compounds could also be measured. Mixtures of MeOH/water containing 10 mM ammonium acetate and 0.2 mM ammonia were used as the eluent. The small amount of ammonia kept the pH of the eluent around 8 so that -COOH was fully deprotonated. These MeOH/water mixtures were prepared in a bottle by mixing predetermined volumes of MeOH, pure water, 1 M ammonium acetate and 0.2 M aqueous ammonia solution. The mixer equipped with the LC pump was not used to mix the eluent components because preliminary experiments that used the LC mixer showed substantial difference in tr values from those determined with premixed eluent.