title: On-site semi-quantitative analysis for ammonium nitrate detection using digital image colourimetry.
abstract: Digital image colourimetry was successfully applied in the semi-quantitative analysis of ammonium nitrate using Griess's test with zinc reduction. A custom-built detection box was developed to enable reproducible lighting of samples, and was used with the built-in webcams of a netbook and an ultrabook for on-site detection. The webcams were used for colour imaging of chemical reaction products in the samples, while the netbook was used for on-site colour analysis. The analytical performance was compared to a commercial external webcam and a digital single-lens reflex (DSLR) camera. The relationship between Red-Green-Blue intensities and ammonium nitrate concentration was investigated. The green channel intensity (IG) was the most sensitive for the pink-violet products from ammonium nitrate that revealed a spectrometric absorption peak at 546 nm. A wide linear range (5 to 250 mgL⁻¹) with a high sensitivity was obtained with the built-in webcam of the ultrabook. A considerably lower detection limit (1.34 ± 0.05mgL⁻¹) was also obtained using the ultrabook, in comparison with the netbook (2.6 ± 0.2 mgL⁻¹), the external web cam (3.4 ± 0.1 mgL⁻¹) and the DSLR (8.0 ± 0.5 mgL⁻¹). The best inter-day precision (over 3 days) was obtained with the external webcam (0.40 to 1.34%RSD), while the netbook and the ultrabook had 0.52 to 3.62% and 1.25 to 4.99% RSDs, respectively. The relative errors were +3.6, +5.6 and -7.1%, on analysing standard ammonium nitrate solutions of known concentration using IG, for the ultrabook, the external webcam, and the netbook, respectively, while the DSLR gave -4.4% relative error. However, the IG of the pink-violet reaction product suffers from interference by soil, so that blank subtraction (|IG-IGblank| or |AG-AGblank|) is recommended for soil sample analysis. This method also gave very good accuracies of -0.11 to -5.61% for spiked soil samples and the results presented for five seized samples showed good correlations between the various imaging devices and spectrophotometer used to determine ammonium nitrate concentrations. Five post-blast soil samples were also analysed and pink-violet product were observed using Griess's test without zinc reduction indicating the absence of ammonium nitrate. This demonstrates significant potential for practical and accurate on-site semi-quantitative determinations of ammonium nitrate concentration.
authors.affiliation: Applied and Environmental Chemistry Research Center, Andaman Environmental Research and Innovation Center, Faculty of Technology and Environment, Prince of Songkla University, Phuket Campus, Phuket 83120 Thailand; Trace Analysis and Biosensor Research Center, Prince of Songkla University, Hat Yai, Songkhla 90112 Thailand; Department of Applied Science, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112 Thailand. Electronic address: choodum@gmail.com.
authors.forename: Aree
authors.initials: A
authors.lastname: Choodum
authors.affiliation: Department of Applied Science, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112 Thailand.
authors.forename: Pichapat
authors.initials: P
authors.lastname: Boonsamran
authors.affiliation: Centre for Anatomy and Human Identification, College of Art, Science and Engineering, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
authors.forename: Niamh
authors.initials: N
authors.lastname: NicDaeid
authors.affiliation: Applied and Environmental Chemistry Research Center, Andaman Environmental Research and Innovation Center, Faculty of Technology and Environment, Prince of Songkla University, Phuket Campus, Phuket 83120 Thailand; Trace Analysis and Biosensor Research Center, Prince of Songkla University, Hat Yai, Songkhla 90112 Thailand.
authors.forename: Worawit
authors.initials: W
authors.lastname: Wongniramaikul
keywords: Ammonium nitrate; Digital image colourimetry; Griess’s test; RGB colour system; Webcam