Technical note | Verification of LC-MS Method Suitability for Application to OPCW Proficiency Testing

Abstract

Defence Science and Technology (DST) Group is working towards becoming a designated laboratory for the Organisation for the Prohibition of Chemical Weapons (OPCW), and thus participates in its proficiency testing program. DST has typically relied on a combination of data from Gas Chromatography-Mass Spectrometry with Electron Impact (GC-MS[EI]) and Gas Chromatography-Mass Spectrometry with Chemical Ionisation (GC-MS[CI]) for reporting purposes, however it has recently implemented a Liquid Chromatography-Mass Spectrometry (LC-MS) method as a third technique to provide additional information where required. Given that samples received as part of the program may be spiked with compounds at concentrations as low as 1 ppm, this document reports the work undertaken in ascertaining that the limit of detection (LOD) of the LC-MS method is below this threshold, and that the method is overall fit for application in OPCW proficiency tests. The results of the work demonstrate that for all compounds assessed, the LOD is below 1 ppm and the method is acceptably repeatable so that it may be used for reporting in OPCW proficiency tests.

Executive Summary

Defence Science and Technology (DST) Group is working towards achieving designated laboratory status with the Organisation for the Prohibition of Chemical Weapons (OPCW). Such laboratories are those which may be used by the OPCW to perform offsite analysis to assist in its investigations pertaining to verification of destruction or alleged use of chemical weapons agents (CWAs). Accordingly, DST regularly participates in the OPCW proficiency testing program to satisfy the OPCW’s condition of at least annual participation in the program, and an A-grade majority maintained across every three tests in which the laboratory has participated.

During a proficiency test, participating laboratories have 15 calendar days in which to analyse the samples and report results. Results reported must have supporting evidence provided by at least two analytical techniques. DST has typically relied on a combination of Gas Chromatography-Mass Spectrometry with Electron Impact (GC-MS[EI]) and Gas Chromatography-Mass Spectrometry with Chemical Ionisation (GC-MS[CI]) data, however it has recently implemented a Liquid Chromatography-Mass Spectrometry (LC-MS)  method as a third technique to provide additional information where required. Given that samples received as part of the program may be spiked with compounds at concentrations as low as 1 ppm, this document reports the work undertaken in the verification of the limit of detection (LOD) of the LC-MS method as being below this level, and that the method is overall fit for application in OPCW proficiency tests.

Herein, solutions of nine hydrolysis products of various (eight) CWAs were prepared at six concentrations in the range 0.25 to 10 ppm, and analysed using the aforementioned method. Results showed that eight of the nine compounds demonstrate a high degree of linearity over the concentration range 0.25 to 10 ppm, and all compounds had an LOD below the 1 ppm threshold, with acceptable repeatability, rendering the LC-MS method fit for participation in OPCW proficiency tests.