Worawit Wongniramaikul

Rapid quantitative colourimetric tests for trinitrotoluene (TNT) in soil

A rapid quantitative colourimetric test was developed for the determination of 2,4,6-Trinitrotoluene (TNT) in soil. Quantification was achieved using an innovative application of photography where the relationship between the Red Green Blue (RGB) value and concentration of colorimetric product was exploited. The wide linear range (1-50 mg/L) and low detection limit (0.73±0.01 mg/L to 3.5±0.4 mg/L) achieved was comparable with spectrophotometric quantification methods. Quantification was validated both with known concentration standards and spiked soil extracts confirming the accuracy of the technique. The results demonstrate a powerful technique with the capacity for development as a rapid on site field test for the analysis of explosives.

Real time quantitative colourimetric test for methamphetamine detection using digital and mobile phone technology

The Simon presumptive color test was used in combination with the built-in digital camera on a mobile phone to detect methamphetamine. The real-time Red-Green-Blue (RGB) basic color data was obtained using an application installed on the mobile phone and the relationship profile between RGB intensity, including other calculated values, and the colourimetric product was investigated. A wide linear range (0.1-2.5mg mL(-1)) and a low detection limit (0.0110±0.0001-0.044±0.002mg mL(-1)) were achieved. The method also required a small sample size (20μL). The results obtained from the analysis of illicit methamphetamine tablets were comparable to values obtained from gas chromatograph-flame ionization detector (GC-FID) analysis. Method validation indicated good intra- and inter-day precision (2.27-4.49%RSD and 2.65-5.62%RSD, respectively). The results suggest that this is a powerful real-time mobile method with the potential to be applied in field tests.

Diisobutyl phthalate degradation by Fenton treatment

Degradation of diisobutyl phthalate (DIBP) by Fenton oxidation was evaluated in this study. The results indicate that the pH, H2O2 and Fe2 + concentration were three main operating factors considerably affecting the decomposition of DIBP. The optimum conditions were observed at pH 3 and the molar ratio of [H2O2]: [Fe2 +]: [DIBP] = 5: 5: 1. Under such condition, the maximum removal of DIBP was as high as 87% at a time of 30 minutes. In general, the empirical equation was derived as follows: (dCDIBP/dt)initial = −k CDIBP,0 0.88CFe2 +,0 0.33CH2O2 0.95.

On-site semi-quantitative analysis for ammonium nitrate detection using digital image colourimetry

Digital image colourimetry was successfully applied in the semi-quantitative analysis of ammonium nitrate using Griesss 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 Griesss 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.

A comprehensive chromatographic comparison of amphetamine and methylamphetamine extracted from river water using molecular imprinted polymers and without the need for sample derivatization

This work explores the differences between two GCMS instruments for the determination of amphetamine and methylamphetamine extracted from water samples (ultra pure water and river water) without the necessity for derivatization. The instruments contained different generations of gas chromatograph and mass selective detector components and revealed significantly different results when presented with the same samples. The extraction methodology also compared two SPE systems. The extraction efficiency of commercially available molecular imprinted polymers as a sorbent in SPE was compared with commonly used hydrophilic balance sorbent. Molecular imprinted polymers provided excellent recoveries (81 ± 2% and 108 ± 3% at 30 μg L(-1), and 94 ± 2% and 94 ± 2% at 200 μg L(-1) for amphetamine and methylamphetamine, respectively). The best LOD obtained was sufficient for the determination of both drugs extracted from river water (0.029 ± 0.003 and 0.015 ± 0.004 μg L(-1) for amphetamine and methylamphetamine, respectively). These were comparable to literature values obtained through conventional extraction and analysis using LC-MS/MS but had the advantage of being achieved using an underivatized GCMS method.

A cost effective hydrogel test kit for pre and post blast trinitrotoluene

A 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.

Portable and selective colorimetric film and digital image colorimetry for detection of iron

Iron is an important trace element in environmental and biological systems, the development of simple and selective methods for the determination of iron is important. In this work, completely biodegradable tapioca starch was introduced as the substrate to entrap standard chromogenic probes (1,10-phenanthroline) for fabrication of a novel colorimetric sensor for ferrous. A clear plasticized thin film from tapioca starch was fabricated inside a small plastic tube as a portable test kit. A red complex was obtained by exposing the film to a ferrous solution, while no color changes were obtained with various other ions, indicating excellent selectivity. The developed films were applied in conjunction with a digital image colorimetry for quantification of ferrous. Calculated molecular absorption of the red complex showed the widest linear range (0 to 10 mg L-1) with good linearity (R2 < 0.9934) with ferrous concentrations. The developed method provided good inter-day precision (1.75 to 3.97%RSD, 5 days 15 sensors), good accuracy (+2.35% to +4.57% relative error), and low detection limit (0.09 ± 0.01 mg L-1). The concentrations of ferrous ion in soil and water samples quantified by the developed method were not significantly different from atomic absorption spectrophotometry at 95% confidence level. The films were stable for at least three months.

A biodegradable colorimetric film for rapid low-cost field determination of formaldehyde contamination by digital image colorimetry

A biodegradable colorimetric film was fabricated on the lid of portable tube for in-tube formaldehyde detection. Based on the entrapment of colorimetric reagents within a thin film of tapioca starch, the yellow reaction product was observed with formaldehyde. Intensity of the blue channel from the digital image of yellow product showed a linear relationship in the range of 0-25 mg L-1 with low detection limit of 0.7 ± 0.1 mg L-1. Inter-day precision of 0.61-3.10%RSD were obtained with less than 4.2% relative error from control samples. The developed method was applied for various food samples in Phuket and formaldehyde concentration range was non-detectable to 1.413 mg kg-1. The quantified concentrations of formaldehyde in fish and squid samples provided relative errors of -7.7% and +10.8% compared to spectrophotometry. This low cost sensor (∼0.04 USD/test) with digital image colorimetry was thus an effective alternative for formaldehyde detection in food sample.