Lab-made colorimetric devices for educational and forensic application

This work is focused on the invention of a spectrometer for colorimetric analysis of tetracycline hydrochloride (TCH), monosodium glutamate (MSG), delta-9-tetrahydrocannabinol (THC), and ethanol (EtOH) with two systems; laser pointer – light dependence resistor (LDR); and paper-based device with smartphone systems.Firstly, a simple spectrometer was designed and invented in our laboratory with simple components such as a laser pointer, light-dependent resistor (LDR), plastic holder, and multi-meter. Three wavelengths of light sources, laser pointers (red, green, and blue), were tested for the relationship of signal (R) in ohm unit and absorbance, using sun-protective car films calibrated to a commercial spectrophotometer. It was found that the relationship of absorbance and log R was linear with the coefficient of determination (R2) > 0.990.The systems were applied to determine tetracycline hydrochloride (TCH) and monosodium glutamate (MSG) using blue and red laser pointers, respectively. The determination of TCH and MSG is based on complex formation with Fe(III) and Cu(II), subsequently producing red and blue color solutions. The optimizations of reagent concentrations were studied. The proposed method presented the linearity in the concentration range of TCH and MSG were 1.15 × 10-4 – 5.74 × 10-6 mol L-1 (R2 0.9987) with LOD 1.44 × 10-6 mol L-1; and 2.96 × 10-3 - 4.73 × 10-2 mol L-1 (R2 0.9987) with LOD 6.50 x 10-4 mol L-1; respectively. The relative standard deviations (%RSDs) of repeatability were 1.30 for TCH and 1.24 for MSG. The proposed spectrometers were applied to determine TCH in pharmaceuticals and MSG in flavor enhancers compared to a commercial spectrophotometer, with no significant difference at a 95% confidence level. Secondly, the capillary-driven microfluidic paper-based device (µCD-PAD) with smartphone-enabled colorimetric detection for on-site analysis was proposed for the simultaneous detection of delta-9-tetrahydrocannabinol (THC) and ethanol (EtOH) in synthetic saliva; based on coupling reaction with fast blue B salt and oxidation reaction with dichromate, respectively. Synthetic salivas with various viscosity can flow to the detection zone without a sample preparation step. Also, the colorimetric signal can be produced on the detection zone without the effect of viscosity (RSD < 5%). Under optimal conditions, the developed device presented the linearity in the concentration range 0.100 – 10.0 mg L-1, with R2 0.9967 and 0.100 – 5.00 %v/v, with R2 0.9943 for THC and EtOH, respectively. The limits of detection (LOD) were 6.00 × 10-2 mg L-1 of THC and 8.00 × 10-2 %v/v of EtOH. The %RSDs for reproducibility were 6.69 (THC) and 4.81 (EtOH). The proposed device was applied to simultaneously detect THC and EtOH in synthetic salivas with acceptable precision and accuracy.