Hydrolysis of VX on Concrete: Rate of Degradation by Direct Surface Interrogation Using an Ion Trap Secondary Ion Mass Spectrometer
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- 作者：Gary S. Groenewold ; John M. Williams ; Anthony D. Appelhans ; Garold L. Gresham ; John E. Olson ; Mark T. Jeffery ; and Brad Rowland
- 刊名：Environmental Science & Technology
- 出版年：2002
- 出版时间：November 15, 2002
- 年：2002
- 卷：36
- 期：22
- 页码：4790 - 4794
- 全文大小：85K
- 年卷期：v.36,no.22(November 15, 2002)
- ISSN：1520-5851
文摘
The nerve agent VX (O-ethyl S-2-diisopropylaminoethylmethylphosphonothiolate) is lethal at very low levels ofexposure, which can occur by dermal contact withcontaminated surfaces. Hence, behavior of VX in contactwith common urban or industrial surfaces is a subjectof acute interest. In the present study, VX was found toundergo complete degradation when in contact with concretesurfaces. The degradation was directly interrogated atsubmonolayer concentrations by periodically performingsecondary ion mass spectrometry (SIMS) analyses afterexposure of the concrete to VX. The abundance of the [VX+ H]+ ion in the SIMS spectra was observed to decreasein an exponential fashion, consistent with first-order orpseudo-first-order behavior. This phenomenon enabled therate constant to be determined at 0.005 min-1 at 25 
C,which corresponds to a half-life of about 3 h on the concretesurface. The decrease in [VX + H]+ was accompaniedby an increase in the abundance of the principal degradationproduct diisopropylaminoethanethiol (DESH), whicharises by cleavage of the P-S bond. Degradation to formDESH is accompanied by the formation of ethyl methylphosphonic acid, which is observable only in the negativeion spectrum. A second degradation product was alsoimplicated, which corresponded to a diisopropylvinylamineisomer (perhaps N,N-diisopropyl aziridinium) that arosevia cleavage of the S-C bond. No evidence was observedfor the formation of the toxic S-2-diisopropylaminoethylmethylphosphonothioic acid. The degradation rate constantswere measured at four different temperatures (24-50C), which resulted in a linear Arrhenius relationship andan activation energy of 52 kJ mol-1. This value agrees withprevious values observed for VX hydrolysis in alkalinesolutions, which suggests that the degradation ofsubmonolayer VX is dominated by alkaline hydrolysiswithin the adventitious water film on the concrete surface.
C,which corresponds to a half-life of about 3 h on the concretesurface. The decrease in [VX + H]+ was accompaniedby an increase in the abundance of the principal degradationproduct diisopropylaminoethanethiol (DESH), whicharises by cleavage of the P-S bond. Degradation to formDESH is accompanied by the formation of ethyl methylphosphonic acid, which is observable only in the negativeion spectrum. A second degradation product was alsoimplicated, which corresponded to a diisopropylvinylamineisomer (perhaps N,N-diisopropyl aziridinium) that arosevia cleavage of the S-C bond. No evidence was observedfor the formation of the toxic S-2-diisopropylaminoethylmethylphosphonothioic acid. The degradation rate constantswere measured at four different temperatures (24-50C), which resulted in a linear Arrhenius relationship andan activation energy of 52 kJ mol-1. This value agrees withprevious values observed for VX hydrolysis in alkalinesolutions, which suggests that the degradation ofsubmonolayer VX is dominated by alkaline hydrolysiswithin the adventitious water film on the concrete surface.