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    Semi-quantitative analysis of formaldehyde in food using calibration chart based on number of colored wells of microwell plate titration
    (2024-10-30)
    Tongdee, Mintra
    ;
    Wilairat, Prapin
    ;
    Praditweangkum, Wiboon
    ;
    Chantiwas, Rattikan
    Microplate titration quantifies sodium hydroxide generated from formaldehyde reacting with excess sulfite in a 96-microwell plate. Phenolphthalein indicators change from red to colorless when all hydroxide ions react. Methodology optimized reagent concentrations, and reaction time and created a Calibration Chart for semi-quantitative determination. The chart shows formaldehyde concentration ranges corresponding to red well counts from 0 to 200 mM in 20 mM increments. Inter-operator repeatability demonstrates precision (3 replicates), correlating red wells with standard formaldehyde concentrations. This instrument-free technique uses readily available commercial plates, eliminating the need for specialized equipment and calibration. The methodology offers simplicity with its reliance on readily available commercial plates and minimal specialized equipment, hence it is cost-effective and easily transportable 96-microwell plates enhancing the methodology's portability, and efficient semi-quantitative analysis of formaldehyde. The analysis of twelve solutions from food samples agrees with the quantitative values using titration.
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    A new creep model for studying the non-linear viscoelastic behavior of cooked white, brown and germinated brown Thai jasmine rice by large deformation testing
    (2018-08-01)
    Sirisomboon, Panmanas
    ;
    Posom, Jetsada
    A new creep model with three parameters for non-linear viscoelastic behavior is proposed as ε<inf>t</inf>=ε<inf>0</inf>(1+[Formula presented]), where the applied stress is constant, ε<inf>t</inf> is the strain at retardation time (t), ε<inf>0</inf> is the initial strain and k<inf>1</inf>, k<inf>2</inf> and n are constants. The relationship has been proved using data derived from cooked Thai Jasmine rice including white, brown and germinated brown rice samples. The creep test at high strain was conducted on scoops of cooked rice using a compression test rig. The model developed showed very accurate prediction performance with coefficients of determination (R<sup>2</sup>) between 0.9991–0.9992 and residual standard errors (RSE) between 0.00030–0.0004.
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    Sequential injection for determination of gamma-aminobutyric acid based on its effect on second order light scattering of silver nanoparticles
    (2016-08-01)
    Jinnarak, Amornrassamee
    ;
    Anantavichian, Pattarapon
    ;
    Intanin, Apichai
    ;
    Fungladda, Suchada
    ;
    Choengchan, Nathawut
    An automated sequential injection (SI) with second order light scattering (SOS) detection for determination of gamma-aminobutyric acid (GABA) was developed. Quantitation is based on electrostatic interaction between GABA and citrate-capped silver nanoparticles (AgNPs). In acetate buffer at pH 3.8, the positively charged GABA induces the nanoparticles to aggregate. This results in a change of light scattering monitored using a spectrofluorometer. In this work, working standard solutions of GABA were prepared in-line by the SI system pumping appropriate volumes of a stock solution of GABA and acetate buffer into a holding coil. Solution of AgNPs was subsequently drawn into the coil. The reaction zone was then transferred to the spectrofluorometer, set with excitation and detection wavelengths at 300 and 600 nm, respectively. Under optimised condition, the SOS intensity was proportional to the concentration of GABA. As a result, a linear curve was obtained in the range of 100–400 mg L<sup>−1</sup> GABA, with a lower limit of detection of 39.6 mg L<sup>‐1</sup>. Good precision of analysis was achieved, with 0.6 and 3.3% relative standard deviation (RSD) for external calibration (n = 5) and standard addition (n = 3), respectively. The developed method was successfully applied for quantification of GABA in dietary supplements (2 samples) and samples of instant green tea (2 samples).