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In the OPCW Proficiency Tests usually two sets of three samples each (test sample, control, blank) are sent for analysis, with no indication for the type of the sample. Each set of samples can be prepared in a different matrix, with organic solvent, water and soil as the most frequent ones. Thus each sample has to be analyzed like a test sample. Participants are requested to identify any chemical contained in the schedules of the Chemical Weapons Convention plus all the degradation products that can originate from them; this involves millions of possible chemicals. Usually, a spiking level of ≈10 ppm is applied. Only chemicals that are considered relevant within the scenario of the proficiency test are to be reported. The choice of sample preparation method strongly depends on the composition of the sample and on the requirements for the different analytical techniques employed in the screening and analysis. Because the sample composition of proficiency test samples is unknown, no target compound sample preparation methods can be applied. New matrices, never used in a PT before, required participants to develop new or to adopt existing sample preparation methods. The new matrices from the 38th OPCW PT were linked to food, biodiesel like used cooking oil methyl ester and a 2% Agar-agar solution (solid gel). Aluminium metal and artificial rainwater chosen to provide matrix challenge for the 40th OPCW PT. The paper provides the challenges that are generated by the new and complex matrices, how to work up gel sample, the tendency of biodiesel to form emulsions, how to sub-sample “metal fragments”, and the method of extractions.

Challenges for Sample Preparation and Analysis of New Matrices During the OPCW Proficiency Tests