Dimethyl Carbonate as a Mobile-Phase Modifier for Normal-Phase and Hydrophilic Interaction Liquid Chromatography

We studied the use of dimethyl carbonate (DMC) as a non-toxic, aprotic modifier for hydrophilic liquid interaction chromatography (HILIC) and as a modifier for normal-phase liquid chromatography (LC). A comparison of ethyl acetate (EA) and DMC as organic mobile-phase modifiers in hexane for normal-phase LC of phthalates was conducted with a silica column and showed that retention factors (k) at the same modifier percentage were about a factor of two greater for DMC. Detection at 215 nm, possible with DMC, allowed for the better detection of the phthalates by a factor of 10, compared with EA detection, best at a 254 nm wavelength. Using a core-shell silica column, HILIC separations of trans-ferulic acid, syringic acid, and vanillic acid were compared between acetonitrile (MeCN) and DMC as the organic portion of the mobile phase, from 80-95%. The analyte retention for DMC, when compared to MeCN, was about 1.5 times greater, with only a moderate increase in back pressure. Plate count and peak asymmetry were somewhat better for the DMC chromatograms, compared to those with MeCN. Seven mono- and di-hydroxybenzoic acid positional isomers could be resolved effectively with DMC. Sorbate and benzoate preservatives in commercial drinks were also determined.