Abstract:

The Chemical Weapons Convention (CWC) requires verification of a large number of compounds with different types and properties. The results of the verification are of great political and military sensitivity. However, the sources of verification samples are complex and diverse, and the contents of the target compounds in these samples are usually very low. These issues increase the likelihood of missed or false detection. Thus, establishing rapid and effective screening methods for the accurate identification of CWC-related compounds in complex environmental samples are of great importance. In this study, a fast and simple procedure based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-electron ionization mass spectrometry (GC-EI/MS) in full-scan mode was developed to determine CWC-related chemicals in oil matrix. A total of 24 CWC-related chemicals with different chemical characteristics were selected to simulate the screening procedure. The selected compounds were divided into three groups based on their properties. The first group included volatile and semi-volatile CWC-related compounds with relatively low polarity, which could be extracted by HS-SPME and directly analyzed by GC-MS. The second group included moderately polar compounds with hydroxyl or amino groups; such compounds are related to nerve, blister, and incapacitating agents. The compounds in the third group included non-volatile CWC-related chemicals with relatively strong polarity, such as alkyl methylphosphonic acids and diphenyl hydroxyacetic acid. These compounds must be derivatized into vaporizable derivatives prior to extraction by HS-SPME and analysis by GC-MS. Variables that influence the SPME process, such as fiber type, extraction temperature and time, desorption time, and derivatization protocol, were optimized to improve the sensitivity of the method. The screening procedure for CWC-related compounds in the oil matrix samples included two main steps. First, low-polarity volatile and semi-volatile compounds (i. e. the first group) were extracted by HS-SPME with divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibers and analyzed in split-injection mode (split ratio, 10∶1) using GC-MS. The use of a large split ratio can reduce the solvent effect, which is conducive to the detection of low-boiling-point compounds. If necessary, the sample could be extracted once more and analyzed in splitless mode. The derivatization agent bis(trimethylsilyl)trifluoroacetamide (BSTFA) was then added to the sample. Mid- and high-polarity compounds (i. e. the second and third groups) were extracted with polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibers after derivatization and analyzed in splitless mode using GC-MS. The established method exhibited good repeatability and sensitivity. The detection limits for the compounds in the first group ranged from 0.5 ng/mL to 100 ng/mL, whereas the detection limits for the compounds in the second and third groups ranged from 20 ng/mL to 300 ng/mL. Except for compounds with extremely high boiling points and a few compounds that are not suitable for derivatization with BSTFA, the method can be used to analyze most CWC-related compounds in oil matrix samples. In particular, it greatly shortened the preparation time of the oil matrix samples and reduced the loss of low-boiling-point compounds owing to the sample concentration process, thereby avoiding missed detection. The method was successfully applied to the Organization for the Prohibition of Chemical Weapons (OPCW) proficiency tests and proved to be a useful technique for the rapid screening of trace levels of CWC-related chemicals in oil matrix.

Key words: headspace solid-phase microextraction (HS-SPME), gas chromatography-mass spectrometry (GC-MS), Chemical Weapon Convention (CWC)-related chemicals, oil matrix, rapid screening