Anal. Chem. 1997, 69, 1866-1872
Determination of Chemical Warfare Agents in Natural Water Samples by Solid-Phase Microextraction Hans-Åke Lakso*
Division of NBC-Defence, FOA, The Swedish Defence Research Establishment, S-90182 Umeå, Sweden Wei Fang Ng
Defence Science Organisation, Ministry of Defence, 20 Science Park Drive, Singapore 118230
A novel analytical technique was developed for detection of nerve agents in natural water samples at ppb and subppb (v/v) levels with GC-SIM and GC-NPD. Four different types of fibers for solid-phase microextraction (SPME) were evaluated, and a method was optimized with respect to sampling time and conditions. It was found that the 65 µm copoly(dimethylsiloxane/divinylbenzene) fiber was the best choice for extraction of the nerve agents. The precision, linear range, and detection limit were investigated for this fiber. Tap water, river water, seawater, and sewage water were spiked with 60 ppb (v/v) of nerve agents, and the samples were monitored for 1 week. This investigation shows that the SPME method is comparable to liquid-liquid extraction and has considerable potential for on-site inspections under the Chemical Weapons Convention. Solid-phase microextraction (SPME) is a new extraction technique which has been developed and commercialized since the beginning of the 1990. This technique combines extraction, concentration, and sample introduction of organic compounds in a single step.1 The more classical extraction techniques like liquid-liquid extraction (LLE), solid-phase extraction (SPE), and purge-and-trap methods have several drawbacks: they are time consuming and/or solvent consuming or very labor intensive. SPME, on the other hand, has none of the above-mentioned drawbacks and uses no solvent. In SPME, a layer of a liquid phase, the stationary phase, is coated on a fused silica fiber. This fiber, with its stationary phase, is kept inside a syringe to protect it between sampling and injection. When sampling is performed, the fiber is simply immersed in an aqueous sample, and extraction thereby begins. Extraction by SPME is a process in which the substances partition between the aqueous phase and the stationary phase on the fiber until equilibrium. After sampling, the fiber is withdrawn into the syringe, and the SPME holder is transferred to the analytical instrument. The fiber is then exposed in the split/ splitless liner in a heated injection port of gas chromatograph for a given period of time, and desorption of the analytes is accomplished. (1) Zhang, Z.; Yang, M. J.; Pawliszyn, J. Anal. Chem. 1994, 66, 844A-853A.
1866 Analytical Chemistry, Vol. 69, No. 10, May 15, 1997
So far, SPME has been used in many different applications, e.g., to extract organochlorine and organophosphorus pesticides2-5 in different matrices. However, nothing has been reported on analyzing chemical warfare agents, e.g., nerve agents, with SPME. The nerve agents are among the most toxic compounds known; therefore, trace detection of these compounds is important for verification. With the imminent ratification of the Chemical Weapons Convention (CWC), there is an escalating need to develop trace analysis methods for these compounds. Trace analysis is also required in matters regarding alleged use of chemical warfare agents. The U.N. Organization for the Prohibition of Chemical Weapons (OPCW) will require sampling techniques that are robust and simple to use in the field when the inspection of the chemical industry under the CWC begins. This work presents the possibility to detect the nerve agents sarin, soman, tabun, and O-ethyl-S-[2-(diisopropylamino)ethyl] methylphosphonothiolate (VX) in natural water samples with SPME. By using selective detection such as gas chromatography nitrogen-phosphorus detection (GC-NPD) and gas chromatography/mass spectrometry selected ion monitoring (GC/MS-SIM), we have demonstrated the usefulness of SPME for trace analysis. This work compares SPME with an established recommended operating procedure (ROP)6 in this area, the liquid-liquid extraction (LLE) technique. EXPERIMENTAL SECTION Materials. Isopropyl methylphosphonofluoridate (sarin), 1,2,2trimethylpropyl methylphosphonofluoridate (soman), ethyl N,Ndimethylphosphoramidocyanidate (tabun), and O-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothiolate (VX) were synthesized in-house at FOA, The Swedish Defence Research Establishment (Umeå, Sweden). The nerve agents are all synthesized in a special laboratory which is built mainly for synthesis of highly toxic compounds. The laboratory has fume hoods with intensified ventilation. The last steps of the synthesis are all done in a glovebox inside these fume hoods to maximize (2) Boyland-Boland, A.; Magdic, S.; Pawliszyn, J. B. Analyst 1996, 121, 929938. (3) Eisert, R.; Levsen, K. J. Am. Soc. Mass Spectrom. 1995, 6, 1119-1130. (4) Young, R.; Lopez-Avila, V.; Beckert, W. J. High Resolut. Chromatogr. 1996, 19, 247-256. (5) Sng, M. T.; Lee, F. K.; Lakso, H-Å. J. Chromatogr. 1997, 759, 225-230. (6) Rautio, M., Ed. Recommended Operating procedures for Sampling and Analysis in the verification of Chemical Disarmament; The Ministry for Foreign Affairs of Finland: Helsinki, 1994. S0003-2700(96)00997-3 CCC: $14.00
© 1997 American Chemical Society
Table 1. Characteristics of Natural Water Samples deionized tap river sea sewage water water water water water turbidity (FNU) COD (mg/L) conductivity (mS/m) pH hardness (deg dH) calcium content (mg/L) magnesium content (mg/L)
0.1
