Introducing dimethyl carbonate as a new eluent in HPLC-ICPMS: Stronger elution with less carbon

Abstract

Inductively coupled plasma mass spectrometry (ICPMS) offers unique possibilities as a chromatographic detector. A major limitation is the difficulty of employing conventional mobile phases in the reversed-phase mode (i.e. containing significant amounts of organic solvents), without a modified instrumental setup that does not retain maximum sensitivity. We introduce dimethyl carbonate (DMC) as a new organic eluent in liquid chromatography with especially desirable properties that enable strong elution under standard ICPMS conditions. A total of eleven model compounds with various properties were tested and the elution behavior was compared with that for common organic eluents. At a concentration of 10% v/v, a mobile phase flow rate of 0.3 mL min-1, and standard ICPMS conditions and set-up, DMC resulted in a stable plasma (reflected power <5 W at a forward power of 1550 W), no significant deposition of carbon on sampler and skimmer cones, and no change in sensitivity following at least 8 hours of continuous operation. At that concentration, DMC decreased the retention factors of compounds on a reversed-phase column by up to 40-fold relative to 10% methanol. When averaged over all compounds tested, it was found that a 10% v/v concentration of DMC was equivalent to 23%, and 48% of acetonitrile and methanol, respectively, none of which showed such compatibility with ICPMS at comparable conditions. Due to its unique chemical structure relative to common solvents, DMC was also found to confer different chromatographic selectivity. DMC yielded similar effects on sensitivity to methanol within the concentration range of 1.0-10% v/v, with signal suppression/enhancement factors within the range of 0.5-4.0 depending on the element. An application involving chlorine speciation in urine is additionally presented. In conclusion, the employment of DMC may facilitate the elution and detection of novel hydrophobic compounds and improve column recovery under standard ICPMS conditions and instrumental set-up without a compromise in detection limits.