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Direct speciation analysis of arsenic in whole blood and blood plasma at low exposure levels by hydride generationcryotrapping- inductively coupled plasma mass spectrometry Tomáš Matoušek, Zhifeng Wang, Christelle Douillet, Stanislav Musil, and Miroslav Stýblo Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b01868 • Publication Date (Web): 15 Aug 2017 Downloaded from http://pubs.acs.org on August 18, 2017
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Analytical Chemistry
Direct speciation analysis of arsenic in whole blood and blood plasma at low exposure levels
by
hydride
generation-cryotrapping-inductively
coupled
plasma
mass
spectrometry Tomáš Matoušeka,*, Zhifeng Wangb,c, Christelle Douilletb, Stanislav Musila and Miroslav Stýblob a
Institute of Analytical Chemistry of the Czech Academy of Sciences, v. v. i., Veveří 97, 602
00 Brno, Czech Republic b
Department of Nutrition, Gillings School of Global Public Health, 2302 MHRC, University
of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7461, USA c
School of Environmental Science & Engineering, Shandong University, 27 Shanda South Rd,
Jinan 250100, China
ABSTRACT A method for analysis of toxicologically important arsenic species in blood plasma and whole blood by selective hydride generation with cryotrapping (HG-CT) coupled either to atomic absorption (AAS) with a quartz multiatomizer or to inductively coupled plasma mass spectrometry (ICP-MS) has been validated. Sample preparation which involved only 5 times dilution with addition of Triton X-100, Antifoam B and L-cysteine suppressed excessive foaming in a hydride generator. Calibration slopes for whole blood and blood plasma spiked with arsenate, monomethylarsonate and dimethylarsinate at 0.25-1 µg L-1 As and 0.025- 0.1 µg L-1 As for AAS and ICP-MS detection, respectively, did not differ from slopes in aqueous solutions. HG-CT-AAS was used to analyze samples with elevated levels of arsenic speciesblood plasma from patients treated with arsenic trioxide for acute promyelocytic leukemia and whole blood from mice fed an arsenic-containing diet. A good agreement between results of the direct analysis and analysis after mild digestion in phosphoric acid proved good efficiency of direct HG-CT procedure for the arsenic species in these types of biological samples. In the next step, plasma and whole blood from healthy donors that were spiked with the plasma from leukemia patients at levels of 0.15-0.4 µg L-1 As were analyzed by direct HG-CT-ICP-MS. Good recoveries for all species even at these low levels (88-104%) were obtained. Limits of detection in blood and plasma were 0.014 µg L-1 for inorganic arsenic and below 0.002 µg L-1 As for methylated arsenic species. Thus, the ultrasensitive direct HG-CT-ICP-MS method is
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Analytical Chemistry
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uniquely suited for analyses of blood plasma and whole blood from individuals at low exposure levels. INTRODUCTION Arsenic is a toxic element present in body fluids in a number of species. From the point of arsenic toxicokinetics and metabolism, the most interesting species found in blood are inorganic arsenic (iAs, either arsenite, iAsIII or arsenate, iAsv) and their methyl derivatives, mono- (MAs) and dimethylated arsenic (DMAs), also in tri- and pentavalent forms. Compared to commonly analyzed urine samples, speciation analysis of arsenic in whole blood and blood plasma is no easy task. In a highly exposed population in Bangladesh, the total arsenic (tAs) concentrations in blood ranged from 1 to 80 µg L-1.1 Thus, in a general, unexposed population the levels of arsenic in whole blood are likely below 1 μg L-1 As, which is on the limit of detection of the workhorse method of speciation analysis, liquid chromatography hyphenated with inductively coupled plasma mass spectrometry (HPLC-ICPMS). Even lower arsenic concentration (often below 0.1 µg L-1) were reported in blood plasma.2 In addition to arsenic concentrations being low, blood or plasma is also a difficult matrix, requiring either dilution or extraction step prior to HPLC separation. Even analysis of tAs in blood or plasma at low exposure levels is very difficult.3 Arsenic species in blood are thought to be bound to proteins,4 which can also be a source of analytical artifacts.5 A recent review of clinical applications of arsenic speciation analysis6 lists only few works on arsenic speciation analysis in whole blood, plasma or serum. Typically these reports only deal with samples with elevated arsenic contents, e.g., from high arsenic exposure areas,7,8,9 from patients undergoing arsenic trioxide treatment5 or after seafood or seaweed ingestion.10,11 For example, in a study examining arsenic species in maternal and cord blood, speciation analysis was successfully performed only in samples with tAs over 10 µg L-1.7 Similarly, Ito et al.12 analyzed 16 pairs of urine/blood samples where concentration in urine exceeded 50 µg L-1; in all but one blood samples only arsenobetaine (AsB) was present above limit of detection (LOD) of 0.3 µg L-1.12 Todorov et al. performed speciation analysis in several blood reference materials containing rather high levels of certified tAs (14-177 µg L-1).13 Also, authors of an interlaboratory study of speciation analysis of caprine blood spiked with individual arsenic species at levels of tAs 3-10 µg L-1 declared that “reasonable results” were obtained considering that the concentrations of arsenic species were close to the measurement LODs of participant laboratories.14 This also illustrates the problem of reference materials suitable for method
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Analytical Chemistry
validation. Although there is plenty of blood, plasma and serum reference materials (SRMs) on the market, only tAs is certified at levels one order of magnitude higher than those typically associated with low exposure, and most of these SRMs use a matrix spiked with arsenic species, as the levels of naturally occurring species are too low. The closest to a low arsenic SRM is NIST 955c Toxic Metals in Caprine Blood Level 1; non-certified reference value 2.07 ± 0.67 µg L-1 tAs (although there have been discrepancies in the interlaboratory study leading to an information value of
