On-site semi-quantitative analysis for ammonium nitrate detection using digital image colourimetry
Aree Choodum1, Pichapat Boonsamran2, Niamh NicDaeid3
1Applied 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.
Science & Justice : Journal of the Forensic Science Society
|December 15, 2015
Summary
Digital image colorimetry offers a practical method for semi-quantitatively analyzing ammonium nitrate (AN) on-site. Using built-in webcams and a detection box, this technique provides sensitive and accurate AN detection, even in soil samples.
Area of Science:
- Analytical Chemistry
- Environmental Science
- Forensic Science
Background:
- Ammonium nitrate (AN) is a widely used fertilizer and a key component in explosives.
- Accurate and rapid on-site detection methods for AN are crucial for security and environmental monitoring.
- Traditional analytical methods can be time-consuming and require specialized laboratory equipment.
Purpose of the Study:
- To develop and validate a digital image colorimetry method for the semi-quantitative analysis of ammonium nitrate.
- To assess the performance of built-in and external webcams for on-site AN detection.
- To compare the sensitivity, detection limits, and accuracy of different imaging devices.
Main Methods:
- Utilized Griess's test with zinc reduction for ammonium nitrate detection.
- Developed a custom detection box for reproducible sample illumination.
- Employed netbook and ultrabook built-in webcams for on-site color imaging and analysis.
- Compared analytical performance against external webcams and a DSLR camera.
- Investigated the relationship between Red-Green-Blue (RGB) color intensities and AN concentration.
Main Results:
- The green channel intensity (IG) showed high sensitivity for AN detection, correlating with its absorption peak at 546 nm.
- The ultrabook's built-in webcam achieved a wide linear range (5-250 mgL⁻¹) and a low detection limit (1.34 ± 0.05 mgL⁻¹).
- Blank subtraction was recommended for soil samples due to potential interference, yielding good accuracy (-0.11 to -5.61%) for spiked samples.
- Analysis of seized and post-blast soil samples demonstrated good correlation with spectrophotometric methods and confirmed the absence of AN in some samples.
Conclusions:
- Digital image colorimetry, particularly with built-in webcams, is a viable and sensitive technique for on-site semi-quantitative analysis of ammonium nitrate.
- The method shows potential for practical applications in security, environmental monitoring, and forensic investigations.
- Further optimization, including blank subtraction for complex matrices like soil, enhances the reliability of the on-site AN detection.
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