Employing natural reagents from turmeric and lime for acetic acid determination in vinegar sample

Microscale titration of acetic acid using digital colorimetry and paper-based analytical devices

A quantitative method for acid-base titrations in paper-based devices (PADs) is described to analyze acetic acid in vinegar samples. In this work, two different types of PADs were developed: a device for individual spot testing and a microfluidic device. Digital colorimetry was used as the detection method, and the images were acquired using a smartphone and a homemade box with LED lights for controlled image acquisition. Titration curves were built with just eight points, using the R channel based on the gradual color transition from red to blue of litmus, a natural indicator. The endpoint was accurately determined by second derivative calculations. Both systems were applied to fifteen vinegar samples of different types, and good concentration results were obtained in comparison to the reference method. The proposed methodology is simple, fast, environmentally friendly, and surpasses the need for calibration curve construction. Moreover, the subjective endpoint identification is eliminated, and the method was automated to provide a high throughput workflow, suitable for quality control processes and real-time measurements.

Reverse Flow Injection Spectrophotometric Determination of Total Acidity in Beverages Using Butterfly Pea Flower Extract

BACKGROUND

Monitoring total acidity during beverage production is crucial for quality control (QC). The standard acid-base titration, though widely used, is slow and generates hazardous waste through the use of acid-base indicators.

OBJECTIVE

To develop an analysis method for beverage samples to determine total acidity using a natural reagent from butterfly pea flower as the colorimetric reagent.

METHODS

The determination of total acidity in beverages was based on the reaction of citric acid with anthocyanin extracted from butterfly pea flowers. The decreased absorbance of anthocyanin was measured at 620 nm. A two-line reverse flow injection manifold was used to perform online dilution of samples.

RESULTS

Under optimal conditions, the calibration curve equation 1/A = 0.03782C + 0.00241 (A = absorbance and C = concentration) was linear over a range of 0.050-0.25% (w/v) citric acid. The LOD and LOQ were 0.0123 and 0.0409% (w/v), respectively. The system achieved a throughput of 120 samples per hour with comparable accuracy and precision to the standard titrimetric method.

CONCLUSION

The injection of butterfly pea flower extract into beverage samples with online dilution in a reverse flow injection system (FIS) was reported for the first time for the determination of total acidity.

HIGHLIGHTS

Use of a green reagent in the method reflects its alignment with the principles of green analytical chemistry, providing a rapid and straightforward solution.

Multifunctional Finishing of Cotton Fabric with Curcumin Derivatives Coatings Obtained by Sol-Gel Method

Textile materials with fluorescent, repellent, or antimicrobial properties are increasingly used in common applications. Obtaining multi-functional coatings is of wide interest, especially for applications related to signaling or to the medical field. In order to increase the performance (color properties, fluorescence lifetime, self-cleaning or antimicrobial properties) of textile materials with special uses, a series of research was carried out regarding the modification of surfaces with nanosols. In this study, coatings with multiple properties were obtained by depositing nanosols on cotton fabrics generated through sol-gel reactions. These multifunctional coatings are hybrid materials in which the host matrix is generated using tetraethylorthosilicate (TEOS) and network modifying organosilanes:dimethoxydimethylsilane (DMDMS) or dimethoxydiphenylsilane (DMDPS) in a 1:1 mass ratio. Two curcumin derivatives were embedded in siloxane matrices, a yellow one (CY) that is identical to bis-demethoxycurcumin (one of the natural constituents in turmeric) and a red dye (CR) that has a N,N-dimethylamino group grafted in position 4 of the dicinnamoylmethane skeleton of curcumin. The nanocomposites obtained by embedding curcumin derivatives in siloxane matrices were deposited on cotton fabric and studied in relation to the dye and the type of host matrix. Fabrics coated with such systems provide a hydrophobic surface, have fluorescent and antimicrobial properties, change color depending on the pH, and therefore can be used in various fields where textiles provide signaling properties, self-cleaning, or antibacterial protection. The coated fabrics maintained their good multifunctional properties even after several washing cycles.

A rapid cotton swab for on-site screening of coloring curcumin on durian skin: food safety aspects

Exported durians from Thailand are sometimes immersed in curcumin to give the fruits a good appearance. Curcumin is regarded as non-toxic additive, however some importing countries prohibited use of any additive to fresh fruits and vegetables. This work aims to develop a rapid, low cost and convenient cotton swab device for curcumin detection. The detection principle involves a colorimetric acid-base characteristic of curcumin. Curcumin in an acidic/neutral solution presents a bright yellow color, while it displays an intense orange-red color in basic solution. A cotton swab acted for both sample collection and as a sensing platform. A pre-moistened swab was used to wipe a durian surface. Afterward, a NaOH solution was dropped onto the swab. A distinct orange-red color appearing on the swab indicates the presence of curcumin. The cotton swab was applied for qualitative analysis of curcumin contaminated on durian husks via visual detection. The developed device provided good reliability, 93.75% (36 samples). Furthermore, the device was demonstrated for quantitative determination using camera detection. Two linear calibrations were obtained in ranges of 10-75 and 75-250 mg L^-1, with a detection limit of 3.2 mg L^-1. The method was also successfully applied to quantification of curcumin in durians (three samples) and dietary supplements (two samples). The test can be done in a few minutes. The developed device was established as an useful tool for food safety and control of contamination by curcumin in an on-site application.

Ultrasound-Assisted One-Pot Cloud Point Extraction for Iron Determination Using Natural Chelating Ligands from Dipterocarpus intricatus Dyer Fruit

An ultrasound-assisted, one-pot cloud point extraction was developed for the determination of iron in vegetable samples by UV-Visible spectrophotometry. This method was based on the complexation of iron with an environmentally-friendly natural chelating agent extracted from Dipterocarpus intricatus Dyer fruit at pH 5.5 in the presence of Triton X-114. Reagent extraction, complexation, and preconcentration were performed simultaneously using ultrasound-assisted extraction at 45 °C. The surfactant-rich phase was diluted with ethanol and loaded through a syringe barrel packed with cotton that acted as a filter to trap the reagent powder. Analyte-entrapped on cotton was eluted using 0.1 mol·L⁻¹ nitric acid solution. Filtrate and eluate solutions were measured absorbance of the dark-blue product at 575 nm. Influential parameters for the procedure were investigated. Under the optimum experimental conditions, the calibration curve was linear, ranging from 0.1 to 1.0 mg·L⁻¹ with r² = 0.997. Limits of detection and quantification were 0.03 and 0.09 mg·L⁻¹, respectively while precision values of intra-day and inter-day were less than 5%. Recovery at 0.5 mg·L⁻¹ ranged from 89.0 to 99.8%, while iron content in vegetable samples ranged from 2.45 to 13.36 mg/100 g. This method was cost-effective, reliable, eco-friendly, and convenient as a green analytical approach to determining iron content.

Modeling the Properties of Curcumin Derivatives in Relation to the Architecture of the Siloxane Host Matrices

Research in the field of natural dyes has constantly focused on methods of conditioning curcumin and diversifying their fields of use. In this study, hybrid materials were obtained from modified silica structures, as host matrices, in which curcumin dyes were embedded. The influence of the silica network structure on the optical properties and the antimicrobial activity of the hybrid materials was monitored. By modifying the ratio between phenyltriethoxysilane:diphenyldimethoxysilane (PTES:DPDMES), it was possible to evaluate the influence the organosilane network modifiers had on the morphostructural characteristics of nanocomposites. The nanosols were obtained by the sol-gel method, in acid catalysis. The nanocomposites obtained were deposited as films on a glass support and showed a transmittance value (T measured at 550 nm) of around 90% and reflectance of about 11%, comparable to the properties of the uncovered support. For the coatings deposited on PET (polyethylene terephthalate) films, these properties remained at average values of T550 = 85% and R550 = 11% without significantly modifying the optical properties of the support. The sequestration of the dye in silica networks reduced the antimicrobial activity of the nanocomposites obtained, by comparison to native dyes. Tests performed on Candida albicans fungi showed good results for the two curcumin derivatives embedded in silica networks (11-18 mm) by using the spot inoculation method; in comparison, the alcoholic dye solution has a spot diameter of 20-23 mm. In addition, hybrids with the CA derivative were the most effective (halo diameter of 17-18 mm) in inhibiting the growth of Gram-positive bacteria, compared to the curcumin derivative in alcoholic solution (halo diameter of 21 mm). The results of the study showed that the presence of 20-40% by weight DPDMES in the composition of nanosols is the optimal range for obtaining hybrid films that host curcumin derivatives, with potential uses in the field of optical films or bioactive coatings.

Infrared thermal imaging combined with paper microzone plates and natural reagent extracts for simple, fast, and green enthalpimetric analysis

Paper microzone plates and thermal infrared enthalpimetry (TIE) were combined with potato juice as natural reagent extract to perform the determination of hydrogen peroxide in pharmaceutical, bleaching, and toiletry products. A multichannel pipette was used for reagent addition simultaneously in multiple zones of paper devices, and the temperature rise was determined using an infrared camera. In order to provide suitable measurements, some parameters were optimized such as pH, volume of reagents, and stability of the extract. Results for the hydrogen peroxide were compared with those obtained using methods from official compendia (United States Pharmacopeia and ASTM D2180-17), with agreements ranging from 96 to 103%. The green analytical procedure index was used to compare the greenness of the proposed method with official ones, with clear advantages for TIE. Only microliters of samples and natural reagent extracts were required for analysis, and it was found that waste generation could be greatly reduced. After analysis, the paper device could be directly disposed since the final products of the reaction were O₂ and water. According to these features, the proposed method could be considered a promising alternative to routine analysis in agreement with green analytical chemistry principles.