General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain.• You may freely distribute the URL identifying the publication in the public portal. Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. ABSTRACTA cost effective hydrogel test kit was successfully developed for the detection of pre-and post-blast trinitrotoluene (TNT). A polyvinyl alcohol (PVA) hydrogel matrix was used to entrap the potassium hydroxide (KOH) colourimetric reagent. The easily portable test kit was fabricated in-situ in a small tube to which the sample could be added directly. The test kit was used in conjunction with digital image colourimetry (DIC) to demonstrate the rapid quantitative analysis of TNT in a test soil sample. The built-in digital camera of an iPhone was used to capture digital images of the colourimetric products from the test kit. Red-Green-Blue (RGB) colour data from the digital images of TNT standard solutions were used to establish a calibration graph. The validation of the DIC method indicated excellent inter day precision (0.12-3.60%RSD) and accuracy (93-108% relative accuracy). Post-blast soil samples containing TNT were analysed using the test kit and were in good agreement with spectrophotometric analysis. The intensity of the RGB data from the TNT complex deviated by +6.3%, +5.1%, and -4.9% after storage of the test kits in a freezer for 3 months. The test kit was also reusable for up to 12 times with only -5.4%, +0.3%, and +4.0% deviations. The hydrogel test kit was applied in the detection of trace explosive residues at the scene of the recent Bangkok bombing at the Ratchaprasong intersection and produced positive results for TNT demonstrating its operational field application as a rapid and cost effective quantitative tool for explosive residue analysis.