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3º Encontro Brasileiro sobre Especiação Química
27 – 30 de novembro de 2012
Bento Gonçalves - RS
The role of reference materials in trace element speciation
Zoltan Mester.
[email protected]
National Research Council Canada
An overview of the current state of the art of Se and As speciation will be given with a special
focus on associated Certified Reference Material (CRM) development. The examples of
SELM (selenium enriched yeast reference material) and DORM / DOLT (marine tissue
CRMs) CRMs will be used to demonstrate the developmental challenges and appropriate
use of these materials.
Selenium
Saccharomyces cerevisiae and many other microorganisms have the remarkable ability to
accumulate large quantities of metallic/metalloid elements. This ability has been exploited for
the production of yeast based mineral supplements which have been used for decades.
However, the efficacy/toxicity of trace element is depends on its chemical form (i.e.
speciation).
Using high resolution orbitrap mass spectrometry the selenium analogs of the key
metabolites of the sulfur amino acid pathway has been identified in selenium enriched yeast.
Oxidized forms of selenocysteine, selenohomocystine, selenoglutathione, seleno-γ-glutamylcysteine,
N-(2,3-dihydroxy-1-oxopropyl)-selenocysteine,
N-(2,3-dihydroxy-1-oxopropyl)selenohomocysteine, selenomethionine, seleno-S-adenosylhomocysteine, the conjugate of
glutathione and N-(2,3-dihydroxy-1-oxopropyl)-selenocysteine, and many others were
identified in Se enriched yeast.
Additionally as sizeable portion of Se in Se enriched yeast is actually in the zero valent form
in nanometer sized deposits as identified using a various synchrotron based X-ray imaging
techniques and nano secondary ion-mass spectrometry.
Arsenic
Isotope dilution mass spectrometry (ID-MS) technique has been widely employed for trace
element determinations. Species specific isotope dilution MS when it is used provide a
number of advantages including: i, it result in enhanced precision and accuracy of the results
as the species specific spike serves as an ideal internal standard; ii, matrix effects are
accounted for since quantitation is based on ratio measurements; iii,nonquantitative analyte
recovery during subsequent sample manipulation does not impact the final results; , species
alteration during sample workup can be assessed.
Unfortunately, arsenic is a monoisotopic element and the ICPMS does not detect C, O, and
H well, thus preventing the use of ID for the determination of arsenic species. On the other
hand electrospray MS could potentially be used for the detection of organic stable isotope
labels.
Here we report the application of isotope dilution LC-LTQ-Orbitrap-MS for the determination
of AsB using a 13C enriched species specific spike synthesized at NRC. For comparison
purposes, standard addition calibration was applied to the determination of AsB in biological
CRMs using LC-ICPMS. The quality and chemical and isotopic purity was assessed using
quantitative NMR.