Complementary molecular and elemental detection of speciated thioarsenicals using ESI-MS in combination with a xenon-based collision-cell ICP-MS with application to fortified NIST freeze-dried urine

Abstract

The simultaneous detection of arsenic and sulfur in thioarsenicals was achieved using xenon-based collision-cell inductively coupled plasma (ICP) mass spectrometry (MS) in combination with high-performance liquid chromatography. In an attempt to minimize the (16)O(16)O(+) interference at m/z 32, both sample introduction and collision-cell experimental parameters were optimized. Low flow rates (0.25 mL/min) and a high methanol concentration (8%) in the mobile phase produced a fourfold decrease in the m/z 32 background. A plasma sampling depth change from 3 to 7 mm produced a twofold decrease in background at m/z 32, with a corresponding fourfold increase in the signal associated with a high ionization surrogate for sulfur. The quadrupole bias and the octopole bias were used as a kinetic energy discriminator between background and analyte ions, but a variety of tuning conditions produced similar (less than twofold change) detection limits for sulfur ((32)S). A 34-fold improvement in the (32)S detection limit was achieved using xenon instead of helium as a collision gas. The optimized xenon-based collision cell ICP mass spectrometer was then used with electrospray ionization MS to provide elemental and molecular-based information for the analysis of a fortified sample of NIST freeze-dried urine. The 3sigma detection limits, based on peak height for dimethylthioarsinic acid (DMTA) and trimethylarsine sulfide (TMAS), were 15 and 12 ng/g, respectively. Finally, the peak area reproducibilities (percentage relative standard deviation) of a 5-ppm fortified sample of NIST freeze dried urine for DMTA and TMAS were 7.4 and 5.4%, respectively.

Proposal for novel metabolic pathway of highly toxic dimethylated arsenics accompanied by enzymatic sulfuration, desulfuration and oxidation

“…Simultaneous analyses [33] of m/z 75( 75 As + ) and 32( 32 S + ) of thioarsenic compounds were performed as follows:…”

Systems for the suppression of spectral interferences for inductively coupled plasma mass-spectrometry

“…The increasing popularity is typical for proteomics, including the identification and quantitation of pro teins using heteroatoms (phosphorus and sulfur), and metallomics-investigation of traces of metals in liv ing organisms [97][98][99][100]. The determination of sulfur [60,101,102], phosphorus [60,[103][104][105] and sele nium [106][107][108] at low levels using quadrupole ICP MS instrument becomes possible only by means of gas filled cells.…”

Atomic Spectrometry Update. Elemental speciation

“…In the measurement of thioarsenicals in urine by HPLC-ICP-MS, the use of Xe as a collision gas gave a much improved LOD down to about 10 ng g À1 for S at m/z 32 than that obtained with He, presumably because of the greater efficiency with which 32 O 2 + was dissociated. 228 A study on the role of S in arsenic cycling found that the oxidation of As III was linked to the presence of S-oxidising bacteria and that the production of As V was greatly enhanced by the addition of sulfide or thiosulfate. 229 The rate and extent of these processes was linked to the concentration of bacteria and the reduced-S:As III ratio.…”