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Analysis of Sarin Nerve Agent Metabolites by Tandem GC Mass Spectrometry and Positive Ion Chemical Ionization
by Jessie Butler and Meredith Conoley, Thermo Electron Corp.
Detecting low levels of chemical agents in a biological matrix has historically been a challenging task. Using Thermo Electron Corporation's innovative GC/MS technologies, rapid and extremely sensitive analyses can be performed.
click the image to enlarge
Figure 1:Top: A spiked urine sample is shown in sequential Full Scan, MS/MS, and MS/MS/MS in PCI with isobutene;
Bottom: The MS/MS/MS product ion spectrum for MPA-TMS shows product ions: 73, 151, 195 m/z. |
Introduction
Rapid analysis of low-level compounds is of utmost importance in security situations. Improved methods for diagnosing chemical agents have become a necessary component of homeland security initiatives. One of the most lethal chemical warfare agents is sarin, an organophosphorus nerve gas developed during WWII as a by-product of pesticides research. Thermo Electron's Finnigan™ PolarisQ™ ion trap mass spectrometer is an effective tool used in the rapid analysis of sarin metabolites in urine at low concentrations. This method provides extreme sensitivity and efficiency while overcoming past obstacles inherent in forensic analysis.
Experimental Conditions
A pesticide column, Restek Rtx-CLPesticide, was used for separation of the TMS derivatives of methyl phosphonic acid (MPA) and isopropyl methyl phosphonic acid (IPMPA). Standards were purchased from Cerilliant Corporation. The Programmable Temperature Vaporizing (PTV) Injector was optimized for a cold splitless injection using a glass silanized liner. The urine samples were passed through a cartridge and then spiked, prior to derivatization, to generate a calibration curve in matrix. The derivatized standards were run in EI Full Scan to determine their retention times and then in PCI using isobutane to generate the molecular ion (M+1). The MS/MS parameters were optimized to generate their unique product ion spectrum.
Results and Conclusions
A calibration curve in urine (25 ng/mL to 500 ng/mL) gave an R2 0.998. The analysis was run in sequential Full Scan and MS/MS. To test the robustness of the method, 60 injections of spiked urine were made with a precision of 9.5% RSD for the internal standard, IPMPA-d7-TMS.
In conclusion, a method was validated for the analysis of sarin metabolites: MPA and IPMPA in urine. The extracts were derivatized with BSTFA to form the trimethyl silyl esters (TMS) prior to analysis by GC-MS/MS by cold splitless injection with a PTV. The Finnigan PolarisQ was used in PCI with isobutane to generate the M+1 molecular ion for isolation from the urine matrix by tandem mass spectrometry. An MS/MS/MS scan was set up for MPA-TMS and MS/MS for IPMPA-TMS (Figure 1). As the results show, this method is effective in detecting and analyzing small amounts of compounds with greater sensitivity by eliminating matrix interference.
References
1. W. Creasy, et al., Journal of Chromatography A, 709 (1995): 333.
2. Jack Driskell, "Quantitation of Organophosphorus Nerve Agent Metabolites in Human Urine Using Isotope Dilution Gas Chromatography-Tandem Mass Spectrometry," Journal of Analytical Toxicology 26 (January/February 2002): 8.
Thermo Electron Corp.
2215 Grand Avenue Parkway
Austin, TX 78728
p A
Thermo Scientific
2215 Grand Avenue Pkwy.
Austin, TX, 78728-3812
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