Interlaboratory development and proposition for a new quality control sample for chemical forensics analysis of chemical warfare agents

A new quality control (QC) test sample for gas chromatography–mass spectrometry (GC–MS) was created and analysed to test the comparability and repeatability of chemical forensics results within the Organisation for the Prohibition of Chemical Weapons (OPCW)–designated laboratories. The QC test sample was designed in collaboration between four laboratories and consists of 27 compounds which evaluate the performance of GC–MS instruments. This solution was analysed with GC–MS(EI) in 11 laboratories, seven of which were OPCW designated. The participating laboratories analysed the sample multiple times on consecutive days, as well as after the analysis of a set of complex matrix samples. Retention times, retention indices, peak areas, peak tailing values, signal-to-noise ratios, and isotope ratios were extracted from the GC–MS data, and statistical multivariate analyses with principal component analysis and Hotelling's T2-tests were conducted. The results from these analyses indicate that differences between GC–MS analyses by multiple laboratories were not statistically significant at the 5% level, as the approximate p-value for the null hypothesis of “no differences between the runs” was 0.69. However, similar data processing methods and data normalisation are essential for enabling the reliable comparison of chemical fingerprints between laboratories. A composition for the QC sample and criteria for acceptable GC–MS performance for chemical forensics are proposed. The composition and criteria differ from the currently used chemical weapons verification analysis QC sample by e.g. broadening the range for retention index calculations by addition of new alkane compounds, including new chemicals with concentrations close to the limit of detection (10–100 ng/ml), and including compounds with higher polarity to emulate real-life forensic samples. The proposed criteria include monitoring of retention indices, isotope ratios, peak tailing, signal-to-noise ratios, peak height, mass spectra, and sensitivity of the instrument. The new compounds and criteria will be the subject of future confidence building exercises to validate their relevancy on a large scale.</p

Generation and Characterization of Six Recombinant Botulinum Neurotoxins as Reference Material to Serve in an International Proficiency Test.

&lt;p&gt;The detection and identification of botulinum neurotoxins (BoNT) is complex due to the existence of seven serotypes, derived mosaic toxins and more than 40 subtypes. Expert laboratories currently use different technical approaches to detect, identify and quantify BoNT, but due to the lack of (certified) reference materials, analytical results can hardly be compared. In this study, the six BoNT/A1-F1 prototypes were successfully produced by recombinant techniques, facilitating handling, as well as improving purity, yield, reproducibility and biosafety. All six BoNTs were quantitatively nicked into active di-chain toxins linked by a disulfide bridge. The materials were thoroughly characterized with respect to purity, identity, protein concentration, catalytic and biological activities. For BoNT/A₁, B₁ and E₁, serotypes pathogenic to humans, the catalytic activity and the precise protein concentration were determined by Endopep-mass spectrometry and validated amino acid analysis, respectively. In addition, BoNT/A₁, B₁, E₁ and F₁ were successfully detected by immunological assays, unambiguously identified by mass spectrometric-based methods, and their specific activities were assigned by the mouse LD50 bioassay. The potencies of all six BoNT/A1-F1 were quantified by the ex vivo mouse phrenic nerve hemidiaphragm assay, allowing a direct comparison. In conclusion, highly pure recombinant BoNT reference materials were produced, thoroughly characterized and employed as spiking material in a worldwide BoNT proficiency test organized by the EQuATox consortium.&lt;/p&gt;</p