Yao, YJ; Khan, MR; Ong, CP; Lee, HK; Li, SFY
A procedure for optimizing the gradient elution reversal phase high performance liquid chromatographic (HPLC) separation of dimethyl-phthalate (131113) (DMP), diethyl-phthalate (84662) (DEP), dibutyl-phthalate (84742) (DBP), benzyl-n-butyl-phthalate (85687) (BBP), diallyl-phthalate (131179) (DAP), and bis(2-ethylhexyl)phthalate (117817) (DEHP) was developed. Mixtures of DMP, DEP, DBP, BBP, DAP, and DEHP were injected into an HPLC system containing an ultraviolet detector and ODS or C18 columns. The mobile phase consisted of various combinations of water, methanol, acetonitrile, and isopropanol. The optimum mobile phase composition to obtain a complete separation of DMP, DEP, DBP, BBP, DAP, and DEHP was determined using the isoselective multisolvent gradient elution (IMGE) technique. This involved calculating the resolution between adjacent chromatographic peaks from the corresponding retention times and peak widths. The resolution values were then used to fit the data to a second order polynomial which contained the volume fractions of water, methanol, acetonitrile, and isopropanol as independent variables. The polynomials were then used to compute resolution contour maps. The resolution contour maps revealed a solvent triangle which specified the proportion of water, methanol, acetonitrile, and isopropanol that would separate DMP, DEP, DBP, BBP, DAP, and DEHP with the desired resolution. A gradient run having an initial mobile phase composition of 68.0:32.0 acetonitrile/water and a final mobile phase composition of 97.0:3.0 acetonitrile/water was shown to completely separate DMP, DEP, DBP, BBP, DAP, and DEHP within 27 minutes. The authors conclude that the IMGE approach can determine optimum conditions for separating components in a mixture with the desired resolution faster and easier than the conventional trial and error approach.
