Lewisite analytical methods

E.R.J. Wils, Trace analytical methods for the analysis of lewisite residues, in Environmental Aspects of Converting CW Facilities to Peaceful Purposes, R.R. McQuire and J.C. Compton (fids), Kluwer Academic Publishers, Dordrecht, 115-122, 2002. 

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). 

Once incorporated, unbound lewisite is quickly hydrolyzed. Its predominant metabolite is 2-chlorovinylarsonous acid, CVAA (Figure 50.8). Analytical methods to confinn lewisite exposure have, at least in the past, focused on the detection and quantification of CVAA. However, Noort et al. (2002) also pointed out that due to the high affinity of arsenic towards sulfhydryl groups, adducts of lewisite/ CVAA and cysteine residues of proteins are formed. In an in vitro study, incubating " C-labeled lewisite with human blood samples, 90% of lewisite was found in erythrocytes, whereas 25 to 50% of arsenic was bound to globin. From these protein adducts, CVAA can be released to form an adduct with the antidote British Anti-Lewisite (BAL) (Fidder et al, 2000). The authors were also able to identify a specific protein adduct of lewisite formed with the cysteine residues 93 and 112 of P-globin. See Detection of DNA and protein adducts of vesicants, below, for analytical... 

Analytical Methods for Urine and Blood. Specific biomarkers of lewisite exposure are currently based on a very limited number of in vitro experiments (Jakubowski et al., 1993 Wooten et al., 2002) and animal studies (Logan et al., 1999 Fidder et al., 2000). Wooten et al. (2002) developed a solid-phase microextraction (SPME) headspace sampling method for urine samples followed by GC-MS analysis. It is the most sensitive method reported to date with a lower limit of detection of 7.4 pg/mL. Animal experiments have been limited in number and in their scope. In one study of four animals, guinea pigs were given a subcutaneous dose of lewisite (0.5 mg/kg). Urine samples were analyzed for CVAA using both GC-MS and GC coupled with an atomic emission spectrometer set for elemental arsenic (Logan et al., 1999). The excretion profile indicated a very rapid elimination of CVAA in the urine. The mean concentrations detected were 3.5 pg/mL, 250 ng/mL, and 50 ng/mL for the 0-8, 8-16, and 16-24 h samples, respectively. Trace level concentrations... 

The workshop revealed that analytical methods do exist to effectively support the destruction of chemical munitions. This is not to say that faster, more sensitive methods are not needed, especially in the area of organo-arsenicals (Lewisites). However, the papers presented at this workshop have made an excellent baseline for further advance in the analytical chemistry associated with the destruction of chemical weapons... 

Lattin, F.G., Mehta, U.J., Jakubowski, E.M. etal. (1996) An analytical method for determination of low level airborne exposure levels to lewisite/mustard. National Technical Information Service, pp. 177-180. 

The number of methods to verify an exposure to lewisite is limited. Chlorovinylarsonous acid (CVAA) can be found as the main metabolite in urine, while this compound can also be found as an adduct to hemoglobin (see Table 54.3). The analyte can be analyzed with GC-MS using normal configurations. 

Thus, both methods and equipment for chemical analytic control, elaborated for the purpose of ecologically benign Mustard and Lewisite destruction, must meet a high standard, namely, sensitivity, which is determined by the listed maximum permissible concentrations of toxic chemicals. At the same time, in the framework of each specific technology for detoxication of a specific chemical, it is necessary to perform research to determine what harmful and toxic chemicals may be produced in the technological process and what effects they may have on the environment It is also necessary to determine what are the maximum permissible releases of those chemicals. 

A recent study published in the Chinese Journal of Instrumental Analysis, Fenxi Ceshi Xuebao, showed a detection limit of 500 ng of Sulfur Mustard (HD) by using accelerated solvent extraction-gas chromatography (ASE-GC) coupled with a flame photometric detector (EPD) in the sulfur mode, in soil. In this case, the study showed evidence that ASE results in better recoveries and sensitivity than liquid solid extraction (LSE) [50]. In 1996, a paper was published on a method for the analysis of Lewisite through derivatization of the compound before introduction into a gas chromatograph. In order to simplify the derivatization process, a tube packed with absorbent was used for collection of airborne vapors. If a positive response occurs when screening analytes using a GC coupled with an FPD, then the same sample can be analysed using a GC equipped with an AED for confirmation based on the elemental response to arsenic (in the case of Lewisite) and sulfur (in the case of Sulfur Mustard) within the appropriate GC retention time window [54]. 

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