TITLE

Can we trust mass spectrometry for determination of arsenic peptides in plants: comparison of LC–ICP–MS and LC–ES-MS/ICP–MS with XANES/EXAFS in analysis of Thunbergia alata

AUTHOR(S)
Bluemlein, Katharina; Raab, Andrea; Meharg, Andrew A.; Charnock, John M.; Feldmann, Jörg
PUB. DATE
April 2008
SOURCE
Analytical & Bioanalytical Chemistry;Apr2008, Vol. 390 Issue 7, p1739
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The weakest step in the analytical procedure for speciation analysis is extraction from a biological material into an aqueous solution which undergoes HPLC separation and then simultaneous online detection by elemental and molecular mass spectrometry (ICP–MS/ES-MS). This paper describes a study to determine the speciation of arsenic and, in particular, the arsenite phytochelatin complexes in the root from an ornamental garden plant Thunbergia alata exposed to 1 mg As L−1 as arsenate. The approach of formic acid extraction followed by HPLC–ES-MS/ICP–MS identified different AsIII–PC complexes in the extract of this plant and made their quantification via sulfur ( m/ z 32) and arsenic ( m/ z 75) possible. Although sulfur sensitivity could be significantly increased when xenon was used as collision gas in ICP–qMS, or when HR-ICP–MS was used in medium resolution, the As:S ratio gave misleading results in the identification of AsIII–PC complexes due to the relatively low resolution of the chromatography system in relation to the variety of As–peptides in plants. Hence only the parallel use of ES-MS/ICP–MS was able to prove the occurrence of such arsenite phytochelatin complexes. Between 55 and 64% of the arsenic was bound to the sulfur of peptides mainly as AsIII(PC2)2, AsIII(PC3) and AsIII(PC4). XANES (X-ray absorption near-edge spectroscopy) measurement, using the freshly exposed plant root directly, confirmed that most of the arsenic is trivalent and binds to S of peptides (53% As–S) while 38% occurred as arsenite and only 9% unchanged as arsenate. EXAFS data confirmed that As–S and As–O bonds occur in the plants. This study confirms, for the first time, that As–peptides can be extracted by formic acid and chromatographically separated on a reversed-phase column without significant decomposition or de-novo synthesis during the extraction step.
ACCESSION #
31342649

 

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