We have found dimethyl carbonate (DMC) to be a versatile mobile phase modifier for three different modes of liquid chromatography (LC). DMC is a moderately polar modifier with a lower UV-cutoff than an ester for normal-phase LC. A comparison of ethyl acetate (EA) and DMC as organic mobile phase modifiers in hexane for normal phase LC of phthalates, common plasticizers with environmental and health concerns, using a core-shell silica column was conducted. Data were collected through the separation of dioctyl phthalate, dibutyl phthalate, benzyl butyl phthalate, diethyl phthalate and dimethyl phthalate on a silica column in varying composition of hexanes with EA or DMC (from 90 to 98% hexane and 10 to 2% modifier). Retention factors (k) ranged from &lt;1 to 5 with EA and around 1 to 10 with DMC while plate counts remain similar. Detection at 215 nm, possible with DMC, allowed for better detection of the phthalates by a factor of 10, compared with EA detection, best at 254 nm. We have also shown DMC, being aprotic, can be an effective non-toxic mobile phase substitute for acetonitrile (MeCN) for hydrophilic liquid interaction chromatography (HILIC). The low solubility of DMC (~14% v/v) with water requires the aqueous part of mobile phase to have one part of ethanol mixed with two parts of ammonium acetate buffer. Using a core-shell silica column, separations of trans-ferulic acid, syringic acid, and vanillic acid were compared between MeCN and DMC as the organic portion of the mobile phase at the percentage range from 85 – 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 comparable for both DMC and MeCN mobile phases. Seven mono- and di-hydroxybenzoic acid positional isomers could be resolved effectively with DMC. Under reversed-phase (RP) conditions we observed a shortening of retention times with DMC compared to MeCN. The use of ethanol (EtOH) has also been examined to allow for a comparison between MeCN, EtOH, DMC, and DMC/EtOH mixtures. A high water/low organic mobile phase comparison showed similar retention between EtOH and MeCN and a marked decrease in retention with DMC for test compounds caffeine, sulfathiazole, and two nitroaniline isomers. We have also examined the separation of polycyclic aromatic hydrocarbons with MeCN, EtOH, and DMC/EtOH based mobile phases.

Dimethyl carbonate as a mobile phase modifier for liquid chromatography

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