Analysis of Chemical Warfare Agents in Water Using Single-Drop Microextraction

Abstract

Single-drop microextraction (SDME) is an extraction methodology where the drop plays an essential role as extracts. It was evaluated for the GC-MS determination of nerve agents, one class of the chemical warfare agents (CWAs). Since these nerve agents are highly toxic, it is important to detect the nerve agents in the environmental samples. Several affecting factors including extraction solvents, stirring rate, extraction time, and amounts of salt were optimized. The limit of detections (LODs) were 0.1 -10 ng/mL and the relative standard deviations (RSDs%, n=5) were in the range of 6.3% to 9.0% for four nerve agents. Without pretreatment of the environmental samples, 5-103 fold enrichments and 48-100% recovery were accomplished. These results demonstrated the feasibility of this method for on-site and off-site analysis of water sample collected from suspicious CWAs site.Key Words: Single-drop microextraction, Chemical warfare agents, Nerve agents IntroductionThe Organization for Prohibition of Chemical Weapons (OPCW) inspects relevant industrial or military sites to implement Chemical Weapons Convention (CWC) which bans the development, production, stockpiling, and transferring of these dreadful weapons in various countries.1 This inspection includes various verification activities (on-site analysis by OPCW inspectors in alleged point and off-site analysis designated by OPCW laboratories). A key point of verification activities is to analyze chemical warfare agents (CWAs) regardless of sample types. Therefore, a pre-treatment of CWAs from the complex environmental samples is very important for analyzing its trace. The pre-treatment techniques for analyzing CWAs include liquid-liquid extraction, 2 solid-phase extraction, 3 and solid-phase microextraction. 4 These extraction techniques were adopted when preparing samples of different sample matrices. Each extraction technique has their strengths and weaknesses and can be used according to the properties of sample and matrix.Recently a fast, simple, inexpensive and solvent free sample preparation technique has been used for extracting CWAs from water. This technique, so called liquid-phase microextraction (LPME) can be performed as a pre-treatment which makes extraction and pre-concentration occur simultaneously. This technique involves hollow fiber protected liquid-phase microextraction 5,6 and single-drop microextraction. 7,8 In case of hollow fiber liquid-phase microextraction, a hollow fiber containing organic solvent is attached into the tip of the syringe needle, and the analytes of interesting are extracted into the organic solvent through a thin layer of a hollow fiber and then detected by GC or GC-MS, 9 typically. After the organic solvent is retracted into the syringe, the hollow fiber is discarded. Therefore, a carry-over effect can be removed. The extraction of CWAs and convention related compounds (CRCs) has been carried out using this technique. 5 The CWAs were directly extracted into organic solvent through hollow fiber and the CRCs having low vola...