Detection of arsenosugars from kelp extracts via IC-electrospray ionization-MS-MS and IC membrane hydride generation ICP-MS

The selectivity and the ability to obtain structural information from detec tion schemes used in arsenic speciation research are growing analytical req uirements driven by the growing number of arsenicals extracted from natural products and the need to minimize misidentification in exposure assessment s. Three arsenosugars were extracted from ribbon kelp utilizing accelerated solvent extraction. The three arsenosugars were separated from other arsen icals with near baseline resolution using a PRP-X100 column and a 20 mm (NH 4)(2)CO3 mobile phase at a pH of 9 with IC-ICP-MS detection. Utilizing thes e chromatographic conditions, the molecular weight was determined for each arsenosugar utilizing ion chromatography-electrospray ionization-mass spect rometry (IC-ESI-MS) in the positive ion mode. The molecular weight and rete ntion times for the three arsenicals are 328 u (4.6 min), 482 u (8.2 min) a nd 392 u (14.2 min). The IC-ESI-MS-MS spectra from each of the arsenosugars were compared to the spectra reported in the literature, which were obtain ed via direct infusion of standard materials. All three MS-MS spectra conta in m/z 237, 195 and 97, which are fragments of the base dimethylarsinylribo side common to all the arsenosugars. Adequate sensitivity for each arsenica l was achieved using a 6.1 ng and a 22 ng injection for IC-ESI-MS and IC-ES I-MS-MS, respectively. Given the unavailability of standards, the arsenosug ar distribution was determined via relative chromatographic areas using IC- ICP-MS. The IC-ICP-MS indicated the presence of an arsenic heteroatom withi n the same retention windows in which the arsenosugars were detected via IC -ESI-MS. The IC-ESI-MS and IC-ESI-MS-MS detection scheme provided structura l information but at reduced sensitivity. In an attempt to preserve sensiti vity and improve selectivity of the IC-ICP-MS, an on-line membrane hydride generation detection scheme was evaluated. The hydride system indicated tha t the three unknown peaks (arsenosugars) were not hydride active, thereby s implifying the chromatographic resolution needed to quantitate the more tox icologically important arsenicals, such as MMA, DMA, As(III) and As(V), whi le minimizing the potential for misidentification.