Capabilities of perfluorinated carboxylic acids as ion-pairing agents for arsenic speciation analysis by reversed phase-LC-ESI-MSn

ALTAMIRANO, JORGELINA C.; WUILLOUD, RODOLFO G.; HEITKEMPER, DOUGLAS

Portland, Oregon

Conferencia; 31st FACSS (THE FEDERATION OF ANALYTICAL CHEMISTRY AND SPECTROSCOPY SOCIETIES) CONFERENCE; 2004

THE FEDERATION OF ANALYTICAL CHEMISTRY AND SPECTROSCOPY SOCIETIES

Arsenic is a widely distributed element in environmental systems and occurs in a large variety of species which differ in toxicity, bioavailability and biotransformation. A major analytical challenge of As speciation is the separation of species with different ionic charge, molecule size, and functional organic groups. Several methods involving ion pair-reverse phase-liquid chromatography (IP-RP-HPLC) for the analysis of arsenic species have been developed; however, they have mainly been coupled to element-specific detectors such as ICP-MS and HG-AAS.  These systems provide excellent sensitivity and detection limits, simplicity and short analysis times, but have the fundamental limitation that species identification is based solely on the matching of retention times. Electrospray mass spectrometry (ES-MS) has successfully been used for structural characterization of numerous compounds of biological and environmental interest. Combining information obtained from element-specific detection with that collected from an LC-ESI-MS constitutes a powerful tool for the speciation of arsenic in complex matrices.  The challenge imposed in the present work has been the use of a volatile ion pair reagent, compatible with the ESI-MS that allows the separation of the major arsenic species (neutral, anionic and cationic) in a single chromatographic run. In this sense, several perfluorinated carboxylic acids were evaluated as ion pair agents for RP-HPLC of arsenic species with the goal of being compatible with both ESI-MS and ICP-MS detection. The effect of chromatographic variables including, perfluorinated carboxylic acid concentration, pH, temperature, and nature of organic solvent were examined to obtain complete chromatographic resolution of at least 14 different arsenic species. including monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA), arsenobetaine (AsB), arsenocholine (AsC), and several arylarsenicals used as animal feed additives. These would include p-arsanilic acid (p-ASA), o-arsanilic acid (o-ASA), 4-nitrophenylarsonic acid (4-NPAA), 4-hydroxy-3-nitrophenylarsonic acid (3-NHPAA), p-ureidophenylarsonic acid (p-UPAA), 4-amino-2-hydroxibenzenarsonic acid (4A2HBAA) and 3-amino-4-hydroxibenzenarsonic acid (3A4HPAA). The applicability of the method was demonstrated by the arsenic speciation analysis of several standard reference materials.