Performance metrics based on signal intensity for ion mobility spectrometry--based explosive trace detectors using inkjet printed materials.

Commercial off-the-shelf (COTS) explosive trace detectors (ETDs) have become an integral part of security practices aimed at protecting the public, transportation, and facilities. Despite their widespread deployment, quality control procedures that can evaluate day-to-day instrument performance or differences among units of the same manufacture are in need for development. In this work, we describe the preparation of test materials (TMs) using inkjet printing that have fixed dosing levels of two explosives; 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and pentaerythritol tetranitrate (PETN). The uncertainty in the mass of dispensed solute is 0.8% (nominal 1 ng RDX and 5 ng or 20 ng PETN depending on ETD). TMs are stable under storage for at least 20 days at temperatures consistent with indoor and outdoor environments, and can be used by field personnel at deployed locations. Inkjet printing is shown to provide the necessary control over the spatial distribution of analyte on the substrate, thus limiting the variability in the signal response due to the sample. Measurements of signal intensities for two COTS ETDs were obtained from TMs over multi-year time spans and for multiple units of each ETD. Reproducibility in the signal response is shown to be between 6% and 15% RSD, or approximately double the within-day variability. The large datasets allow for the first time modeling of signal intensities with respect to normal distributions, which support the use of standard 3-sigma control practices.