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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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Multi-well plate as headspaces for paper-based colorimetric detection of sulfur dioxide gas: An alternative method of sulfite titration for determination of formaldehyde
(2023-01-25)
Yodpach, Nattapon
;
Chantiwas, Rattikan
;
Wilairat, Prapin
;
Choengchan, Nathawut
;
Praditweangkum, Wiboon
This work describes the analysis of formaldehyde using a 96-well microplate as multiple headspaces for the separation of sulfur dioxide gas generated from the sulfite remaining after its reaction with the formaldehyde in the sample. The quantitation of the gas is by colorimetric detection of an indicator paper placed over the microplate. The samples are aqueous extracts of various foods that are possibly adulterated with formaldehyde. A known excess amount of sulfite is added to the extract solution aliquoted in the well. The remaining sulfite is acidified with hydrochloric acid to generate sulfur dioxide gas which diffuses through the headspace above the solution to be absorbed at the moist strip of the indicator paper placed over the mouth of the wells. Anthocyanins extracted from the butterfly pea flower is used as the pH indicator giving a color change from the increase of hydrogen ions by hydrolysis of the absorbed sulfur dioxide gas. The exposed paper strip is scanned, and the digital images of the colored region analyzed using ImageJ software. The optimized method has a linear range of 200–1000 mg L−1 formaldehyde with limit of detection ((2.57*SD of intercept)/(slope of calibration line)) of the aqueous extract of 40 mg L−1 and coefficient of determination (r2) > 0.9979. Samples of fresh produce, such as seafood, meat, and vegetables, and various processed food were analyzed for their possible formaldehyde content. The results obtained from the headspace paper-based colorimetric detection are not statistically different from the values obtained from the titration method by paired t-tests.
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A new colorimetric method for determination of formaldehyde in sea food based on anti-aggregation of gold nanoparticles
(2022-12-01)
Mathaweesansurn, Arjnarong
;
Detsri, Ekarat
A new colorimetric method based on anti-aggregation of gold nanoparticles (AuNPs) in the presence of melamine for sensitive and selective determination of formaldehyde was developed. The citrate capped AuNPs was synthesized by Turkevich method. A certain concentration of melamine is responsible for color change of AuNPs from red to purple. The surface plasmon resonance peak was shifted from 520 to 640 nm. In the presence of formaldehyde, the reaction between melamine and formaldehyde to form methylol melamine was occurred, which resulted in the decreasing of aggregation of AuNPs. Based on the anti-aggregation mechanism, formaldehyde can be detected by observing the color change of AuNPs solution containing melamine, which was monitored by UV–visible spectrophotometer. Calibration curve plotted between absorbance ratio (A640/A520) and formaldehyde concentration was made with linearity of 0 – 2000 µg L−1. The limit of detection and the limit of quantitation were found at 26.0 µg L−1 and 88.0 µg L−1, respectively. The method also provided high accuracy (%recovery in range 97.3 – 104%) and high precision (%RSD < 5.6).
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Treatment of formaldehyde-containing wastewater using membrane bioreactor
(2012-03-01)
Jarusutthirak, Chalor
;
Sangsawang, Kamolchanok
;
Mattaraj, Supatpong
;
Jiraratananon, Ratana
Performance of a membrane bioreactor (MBR) in removal of formaldehyde from synthetic wastewater was investigated. Batch tests for biodegradation of formaldehyde indicated that bioreactors containing acclimated sludge were able to remove up to 99.9% of the formaldehyde from solution. The 12-L MBR was equipped with a submerged hollow-fiber ultrafiltration (UF) membrane with 0.85-m2 filtration area. The unit was operated at a hydraulic retention time of 10 h in aerobic mode with formaldehyde as the sole carbon source for microbial growth. The results revealed that the MBR reduced formaldehyde concentration from 526±30 to a 1.39±0.73-mg/L, corresponding to a removal efficiency of 99.73±0.14%. Increasing solid retention time (SRT) resulted in an increase in mixed liquor suspended solids (MLSS), leading to improved efficiency in removal of formaldehyde from the MBR. Flux decline during MBR operation was caused by accumulation of MLSS on the membrane surface. SRT did not affect flux decline, but did affect flux recovery after cleaning. Long SRT (60 days) led to greater flux recovery than shorter SRTs (30 and 10 days). © 2012 American Society of Civil Engineers.

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