Rapid, objective, and defensible detection of chemical warfare agents .CWAs) at incident scenes remains a critical challenge in forensic chemistry. Detector tubes, widely used by military and emergency services, are low-cost and simple but traditionally provide only subjective yes/no results. Here, we demonstrate the first field-deployable approach that upgrades these tubes into semi-quantitative forensic tools by coupling them with an inexpensive portable tristimulus colorimeter that can be operated either directly on-device or via a free Android application.
Using tubes for sarin (GB), hydrogen cyanide (AC), and sulfur mustard (HD), color responses were evaluated in CIE-L*a*b* space. Analytical parameters—including repeatability at fixed spots, intra−/interday precision, calibration models, stabilization times, and colorimetric detection thresholds (CDTs)—were systematically characterized. Instrumental colorimetry reduced CDTs by approximately one order of magnitude (5–20×) compared to conventional naked-eye inspection, providing faster, more reproducible, and quantifiable results. Calibration was linear for AC and HD and followed a power-law model for GB, with uncertainties ≤15 % except for heterogeneous AC layers (≤40 %).
This workflow converts subjective visual inspection into objective, archivable digital records suitable for forensic documentation. Compared to advanced field instruments such as ion mobility spectrometers, it delivers actionable semi-quantitative data at a fraction of the cost and logistical burden. While the method is inherently limited by the heterogeneity of indicator layers and possible matrix effects, these factors do not outweigh its forensic advantages, particularly its enhanced sensitivity, reproducibility, and trace-level applicability for both military and civilian chemical incident response.
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