CVAAS

For PHg, a variety of different filter methods have been applied, such as Teflon or quartz fiber filters. Before analysis, these filters undergo a wet chemical digestion usually followed by reduction-volatilization of the Hg to Hg(0) and analysis using cold vapor atomic absorbance spectrometry (CVAAS) or cold vapor atomic fluorescence spectrometry (CVAFS). Recently, a collection device based on small qrrartz... 

Urine CVAA Solid phase microextraction headspace sampling, followed by GC/MS with El ionisation Deuterated CVAA Phenylarsine oxide LOD 500 ppt Short window for detection. Lack of validation in human samples. 

Blood CVAA (globin bound and free) GC-MS As above LOD InM As above... 

Work Item B determination of mercury by CVAAS after pressure digestion. Work Item C determination of lead and cadmium by ETAAS after dry ashing. Work Item D performance criteria and general considerations. 

Cold vapor atomic absorption (CVAA) spectrophotometry for mercury analysis... 

A simultaneous ICP-AES is the instrument preferred by the laboratories because it provides a fast and sufficiently sensitive analysis of multiple elements. Mercury is the only exception, as the high detection limit of the ICP-AES analysis for mercury does not meet the regulatory requirements. That is why mercury is analyzed with a much more sensitive CVAA technique. 

High concentrations of sulfide may interfere with the CVAA mercury measurement. Free chlorine that is generated in the oxidation step of seawater samples or in other samples with high chloride contents absorbs radiation at 253 nm. Sulfide and chloride can be chemically removed from the sample matrix prior to analysis. 

Figure 6.1 Bar-graph of MeHg in CRM 580. The results correspond to six replicate determinations as performed by different laboratories using various methods. MEANS indicates the mean of laboratory means with 95% confidence interval. Abbreviations-. CVAAS, cold vapour atomic absorption spectrometry CVAFS, cold vapour atomic fluorescence spectrometry ECD, electron capture detection GC, gas chromatography HPLC, high-performance liquid chromatography ICPMS, inductively coupled plasma mass spectrometry MIP, microwave induced plasma atomic emission spectrometry QFAAS, quartz furnace atomic absorption spectrometry SFE, supercritical fluid extraction.

Falter, R. and H.F. Scholer. 1995. Determination of mercury species in natural waters at pictogram level with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS. Fresenius J. Anal. Chem. 353 ... 

Procedures based on GC/MS for the determination of the lewisite 1 decomposition product 2-chlorovinylarsonous acid (CVAA, CAS number 85090-33-1) in urine and blood have also been developed. In one procedure, CVAA is converted with BAL the resulting CVAA/BAL product isolated by SPE on a C18-cartridge and further derivatized with heptafluorobutyryl imidazole (51). A later developed procedure is based on the derivatization of CVAA with 1,3-propanedithiol followed by SPME isolation and GC/MS analysis. Using SIM at the molecular ion peaks, the limit of detection was determined at 7.4 pg per ml urine (52). 

Lewisite is too reactive to be analyzed by LC. Even with GC, it leads to a rapid degradation of column performance. Lewisites 1 and 2 initially hydrolyze to 2-chlorovinylarsonous acid (CVAA) (26) and bis(2-chlorovinyl)arsenous acid (28), respectively. LC/MS analysis of these trivalent acids is problematic, giving very poor signal-to-noise ratios in both... 

No detailed metabolism studies have been reported for lewisite. It is rapidly hydrolyzed to 2-chloro-vinylarsonous acid (CVAA) (13) in the presence of moisture, and Waters and Williams reported that... 

CVAA is excreted in the urine of experimental animals (34). This has since been confirmed by modern analytical methods. 

Trivalent arsenic forms strong bonds with sulfur, and thiols are therefore used for derivatizing both lewisite and CVAA, forming the same derivative (19). Lewisite reacts with mono and dithiols the reaction with dithiols occurring rapidly at ambient temperature. In a competitive environment, lewisite reacts almost exclusively with dithiols rather than monothiols (35). Three dithiols, 1,2-ethanedithiol, 1,3-propanedithiol and 2,3-dimercaptopropan-l-ol (British Anti-Lewisite, BAL) have been used for biomedical sample analysis of CVAA to form cyclic derivatives (14a, b) and (15). Unlike derivatiza-tion of TDG, CVAA can be derivatized direcdy in an aqueous solution. 2,3-Dimercaptotoluene, which has been used extensively for environmental analysis (19), does not appear to have been used. 

Jakubowski et al. (36) developed a GC/MS method for CVAA spiked into guinea pig urine using 1,2-ethanedithiol for derivatization, with phenyl arsine oxide as the internal standard. The same group later expanded the method to include atomic emission detection (AED) (37). CVAA was concentrated from urine (adjusted to pH 6 with 1M HC1) by SPE on Cl8. After elution with methanol and concentration to dryness, the residue was reconstituted and derivatized with ethanolic 1,2-ethanedithiol. Detection was by GC combined with arsenic selective AED and by electron impact/mass spectrometry (EI/MS) using SIM. Ions monitored were the moderately intense M+ ion at mlz 228, an intense ion [M — C2H4]+, mlz 200, and a base... 

The most sensitive method for CVAA has recently been reported by Wooten et al. (39) using solid-phase microextraction to concentrate the derivatized analyte. Urine, with added ammonium acetate buffer and PhAsO as an internal standard, was derivatized directly with 1,3-propanedithiol and the derivative concentrated on a poly(dimethylsiloxane) (PDMS) solid-phase microextraction (SPME) fiber. Analysis was by automated GC/MS using SIM of the isotopic MH+ ions. An impressive detection limit of 7.4pg/ml was reported, using a benchtop GC/MS system. The method was validated using spiked human urine. 

The most generally applied method for determination of an arsenical is by atomic absorption spectrometry (AAS) after reduction of the compound to AsH3. However, this only provides an indication of the presence of the element as against a natural background. Lewisite rapidly hydrolyzes to 2-chlorovinylarsonous acid (CVAA see Figure 7) in an aqueous environment such as blood plasma, and analytical methods have focused mainly on the determination of CVAA (see Chapter 16). 

In view of the high affinity of arsenic for thiol functions, it can be expected that lewisite and CVAA will bind to cysteine residues of proteins. When human blood was incubated with 20 nM to 0.2 mM of [14C]lewisite, 25-50% of the dose became associated with globin (35). Electrospray tandem MS provided evidence for the presence of a CVAA-crosslink between the cysteine-93 and cysteine-112 residues in fi-globin. Whether this was the only type of adduct has not yet been completely elucidated. It must be remarked, however, that this result was in contrast with results obtained by others for the analogous phenyldichloroarsine, for which binding to human hemoglobin could not be observed. 

Figure 7. Chemical structures of 2-chlorovinyldichloroarsine (lewisite LI), 2-chlorovinylarsonous acid (CVAA), British Anti-Lewisite (BAL) and the CVAA-BAL complex...

Figure 8. Chemical structures of 2-chlorovinyldichloroarsine (Lewisite LI), 2-chlorovinylarsonous acid (CVAA), British Anti-Lewisite (BAL) and the CVAA-BAL complex. (Reprinted from Toxicology and Applied Pharmacology, Vol. 184, D. Noort,H.P. BenschopandR.M. Black, Biomonitoring of Exposure to Chemical Warfare Agents A Review, pages 116-126 (2002), with permission from Elsevier Science.)...

As, Sb, and Au determined by instrumental neutron activation analysis (INAA). Hg determined by cold vapor atomic absorption (CVAA). nd = not determined. 

In 2002 extensive kinetic and product studies on the reactions of gaseous Hg with molecular and atomic halogens (X/X2 where X = Cl, Br) were performed at atmospheric pressure (750 1 Torr) and room temperature (298 1 K) in air and N2 [24]. Kinetics of fhe reactions with X/X2 were studied using both relative and absolute techniques. Cold vapour atomic absorption spectroscopy (CVAAS) and gas chromatography with mass spectroscopic detection (GC-MS) were the analytical methods applied. The measured rate constants for the reactions of Hg with CI2, Cl, Br2, and Br were (2.6 0.2) x IQ-i , (1.0 0.2) x 10" , < (0.9 0.2) x and (3.2 0.3) x 10 cm molecule s , respectively. Thus CI2 and Br2 are not important reactants in the troposphere for the CI2 and Br2 concentrations reported in literature [24]. 

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