Phitchan Sricharoen

A novel extraction method for β-carotene and other carotenoids in fruit juices using air-assisted, low-density solvent-based liquid-liquid microextraction and solidified floating organic droplets.

Green extraction using air-assisted, low-density solvent-based liquid-liquid microextraction and solidified floating organic droplets (AA-LDS-LLME-SFOD) prior to spectrophotometry was successfully applied for quantitation of carotenoids in fruit juices. Under optimal conditions, β-carotene could be quantified with a linear response up to a concentration of 60 μg mL(-1). The procedure was performed in a microcentrifuge tube with 40 μL of 1-dodecanol as the extraction solvent and a 1.0 mL juice sample containing 8% NaCl under seven extraction cycles of air pumping by syringe. This method was validated based on linearity (0.2-30 μg mL(-1), R(2) 0.998), limit of detection (0.04 μg mL(-1)) and limit of quantification (0.13 μg mL(-1)). The precision, expressed as the relative standard deviation (RSD) of the calibration curve slope (n=12), for inter-day and intra-day analysis was 4.85% and 7.92%, respectively. Recovery of β-carotene was in the range of 93.6-101.5%. The newly proposed method is simple, rapid and environmentally friendly, particularly as a useful screening test for food analysis.

An iodine supplementation of tomato fruits coated with an edible film of the iodide-doped chitosan.

In general, the risk of numerous thyroid cancers inevitably increases among people with iodine deficiencies. An iodide-doped chitosan (CT-I) solution was prepared for dipping tomatoes to coat the fresh surface with an edible film (1.5 μm), thereby providing iodine-rich fruits for daily intake. Characterisation of the thin film was conducted by FTIR and SEM. Stability of the CT-I film was studied via water immersion at various time intervals, and no residual iodide leached out due to intrinsic interactions between the cationic amino group of chitosan and iodide ions. Moreover, the iodide supplement exhibited no effect on the antioxidant activity of tomatoes. The iodine content in the film-coated tomato was determined by ICP-OES. The tomato coating with 1.5% (w/v) CT-I contained approximately 0.4 μg iodide per gram fresh weight. In addition, the freshness and storability of iodine-doped tomatoes were also maintained for shelf-life concerns.

Core–shell SiO2‐coated Fe3O4 with a surface molecularly imprinted polymer coating of folic acid and its applicable magnetic solid‐phase extraction prior to determination of folates in tomatoes

A novel core-shell magnetic surface molecularly imprinted polymer with folic acid as a template was successfully synthesized by the sol-gel method. To generate Lewis acid sites in the silica matrix for the interaction of the metal coordinate with the template, 3-aminopropyltriethoxysilane was used as a functional monomer, tetraethyl orthosilicate as a cross-linker, and aluminum ions as a dopant. The magnetite encapsulated by the silica shell plays an important role as a magnetic-coated polymer. The synthesized product was characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and FTIR and UV/Vis spectroscopy. The powder X-ray diffraction patterns, FTIR and UV/Vis spectra confirmed the characteristics of the as-prepared silica coated magnetite and folic acid molecularly imprinted polymer. It was successfully applied for magnetic solid-phase extraction prior to the determination of folates in tomato samples using high-performance liquid chromatography with photodiode array detection. The detection limit of the proposed method was 1.67 μg/L, and results were satisfactory, with a relative standard deviation of < 3.94%.

Using bio-dispersive solution of chitosan for green dispersive liquid–liquid microextraction of trace amounts of Cu(II) in edible oils prior to analysis by ICP–OES

A green approach using chitosan solution as a novel bio-dispersive agent for the dispersive liquid-liquid microextraction (DLLME) of trace amounts of Cu(II) in edible oils is presented. An emulsion was formed by mixing the oil sample with 300µL of 0.25% (w/v) chitosan solution containing 200µL of 6molL-1 HCl. Deionized water was used to induce emulsion breaking without centrifugation. The centrifuged Cu(II) extract was collected and analyzed using an inductively coupled plasma-optical emission spectrometer. The detection and quantitation limits were 2.1 and 6.8µgL-1, respectively. Trace amounts of Cu(II) in six edible oil samples were tested under optimum conditions for DLLME, with a recovery ranging from 90.3% to 109.3%. Therefore, the new dispersive agent in DLLME offers superior performance owing to the non-toxic nature of the solvent, short extraction time, high sensitivity, and easy operation.

A Green Extraction of Trace Iodine in Table Salts, Vegetables, and Food Products Prior to Analysis by Inductively Coupled Plasma Optical Emission Spectrometry

In this study, we report a new method for iodine extraction from table salts, vegetables, and other food products using ultrasound-assisted extraction, prior to the iodine determination by inductively coupled plasma optical emission spectrometry. For the ultrasound-assisted extraction, deionized water as the extraction solvent and an extraction time of 5 min were found to be the most optimum condition. A linear calibration curve was plotted for 0.1 to 200.0 mg L−1 iodine convention. The limits of detection and quantification were 0.049 and 0.164 mg L−1, respectively. The precision for intraand inter-day analyses was 2.75 and 4.54%, respectively. The accuracy of the method was confirmed with certified reference materials. Recoveries in 47 real samples were ranged between 80.48 and 118.1%. Therefore, the proposed method could be considered as a rapid, simple, and environmental-friendly method (the green extraction) to determine the trace amounts of iodine in different kinds of food products.

A fluorescence switching sensor based on graphene quantum dots decorated with Hg2+ and hydrolyzed thioacetamide for highly Ag+-sensitive and selective detection

A selective fluorescent sensor based on graphene quantum dots (GQDs) was developed for the determination of silver ions (Ag+). The GQDs were prepared by the citric acid pyrolysis method. In the presence of mercury ions (Hg2+), the fluorescence intensity of the GQDs decreased linearly and it was fully recovered by the hydrolysis of thioacetamide (TAA), giving hydrogen sulfide in the reaction system. This research study was aimed at using the fluorescence turn-off sensor for the selective determination of Ag+. Upon the addition of Ag+, the fluorescence intensity of the generated sulfide-(Hg2+ quenched GQDs) decreased as a linear function of the Ag+ concentration. Then, the acquired GQDs showed steady, selective, and highly sensitive detection of Ag+. The experimental parameters affecting the fluorescence turn-on/off sensor were investigated and optimized. The optimum conditions included 4 μM Hg2+ concentration, 70 μM TAA concentration, solution pH of 7 and a 5 min reaction time. Under the optimized conditions, the working linear concentration range, limit of detection and limit of quantification for Ag+ were 0.5–10.0, 0.18 and 0.60 μM, respectively. The proposed method was successfully applied for the selective determination of trace amounts of Ag+ in five real water samples with satisfying levels of recovery (89.31–114.08%).

Electrolyte-assisted microemulsion breaking in vortex-agitated solidified floating organic drop microextraction for preconcentration and analysis of Sudan dyes in chili products

For the extraction and determination of trace amounts of Sudan I–IV dyes in chili product samples, a simple and efficient liquid phase microextraction technique was developed using electrolyte-assisted microemulsion breaking in vortex-agitated solidified floating organic drop microextraction (VA-SFODME-EAMB) and high performance liquid chromatography. Under optimal conditions, 5.0 mL of sample solution yielded a pre-concentration factor of 62. Linearity (0.5–2500 ng mL−1, R2 > 0.99), the limit of detection (0.16–0.24 ng mL−1), and the limit of quantification (0.53–0.80 ng mL−1) were used to validate this method. The precision, expressed as relative standard deviation (% RSD), was calculated using seven and five experiments with mixed Sudan dyes at a concentration of 500 ng mL−1. Intra- and inter-day analyses validated the % RSD precision data (<3.5 and 7.0%, respectively). For the analyzed real samples, the recoveries of these dyes ranged between 90.1% and 109%. This newly proposed method is simple, rapid, and environmentally friendly without using both a disperser solvent and a centrifugation step to separate the aqueous and organic phases. In particular, it is applicable for food analysis as a useful screening test of illegal adulteration with Sudan dyes.

Feasibility of hard acid–base affinity for the pronounced adsorption capacity of manganese(II) using amino-functionalized graphene oxide

The present study reveals the feasibility of using graphene oxide (GO) functionalized with 3-mercaptopropyl-trimethoxysilane (APTMS) for the removal of Mn(II) from aqueous solution. The APTMS bound on GOs surface was successfully confirmed by FTIR and EDX. For an optimal adsorption study, the effects of pH (pH 1–6), incubation time (5–80 min), temperature (30–60 °C) and initial concentration of Mn(II) (0.1–60 mg L−1) were investigated in association with Mn measurement by AAS. The optimum conditions for Mn(II) removal included a 20 mg L−1 initial concentration with 0.02 mg adsorbent at pH 5.5, and complete adsorption equilibrium was reached within 50 min. Their adsorption models are well described by both Langmuir and Freundlich isotherms. The maximum adsorption capacity of GO-NH2 for Mn(II) was 161.29 mg g−1, about 10 and 4 times higher than those of GP (16.45 mg g−1) and GO (41.67 mg g−1) according to their relevant functional groups. For the GO-NH2 adsorbent, the adsorption process of Mn(II) follows a pseudo-second-order kinetics model, indicating that the overall rate of Mn(II) uptake is controlled by external mass transfer at the initial stage of the adsorption. Later, the driving forces that control the adsorption rate are attributable to an intra-particle diffusion. A thermodynamic adsorption process reveals mainly an exothermic spontaneous reaction. Therefore, the present study provides an excellent adsorbent for Mn(II) from aqueous solution. This adsorbent can also potentially be used for wastewater treatment.

GSH-doped GQDs using citric acid rich-lime oil extract for highly selective and sensitive determination and discrimination of Fe3+ and Fe2+ in the presence of H2O2 by a fluorescence “turn-off” sensor

Synthesis and characterization of graphene quantum dots (GQDs) simultaneously doped with 1% glutathione (GSH-GQDs) by pyrolysis using citric acid rich-lime oil extract as a starting material. The excitation wavelength (λmax = 337 nm) of the obtained GSH-GQD solution is blue shifted from that of bare GQDs (λmax = 345 nm), with the same emission wavelength (λmax = 430 nm) indicating differences in the desired N and S matrices decorating the carbon based nanoparticles, without any background effect of both ionic strength and masking agent. For highly Fe3+-sensitive detection under optimum conditions, acetate buffer at pH 4.0 in the presence of 50 μM H2O2, the linearity range was 1.0–150 μM (R2 = 0.9984), giving its calibration curve: y = 34.934x + 169.61. The LOD and LOQ were found to be 0.10 and 0.34 μM, respectively. The method’s precisions expressed in terms of RSDs for repeatability (n = 3 × 3 for intra-day analysis) were 2.03 and 3.17% and for reproducibility (n = 5 × 3 for inter-day analysis) were 3.11 and 4.55% for Fe2+ and Fe3+, respectively. The recoveries of the method expressed as the mean percentage (n = 3) were found in the ranges of 100.1–104.1 and 98.08–102.7% for Fe2+ and Fe3+, respectively. The proposed method was then implemented satisfactorily for trace determination of iron speciation in drinking water.

The use of S2O82− and H2O2 as novel specific masking agents for highly selective “turn-on” fluorescent switching recognition of CN− and I− based on Hg2+–graphene quantum dots

In this study, we report that both CN− and I− can enhance the fluorescent intensity of Hg2+–graphene quantum dots (Hg2+–GQDs). However, the selectivity of the sensor was poor. Accordingly, simple specific masking agents can be directly used to solve this problem. Here, for the first time, we report the use of persulfate ion (S2O82−) as a turn-on fluorescent probe of Hg2+–GQDs for selective CN− detection, while hydrogen peroxide (H2O2) was selected for its sensing ability towards I− ion detection. Interestingly, the signal was immediately measured after addition of the masking agent to Hg2+–GQDs and the sample because its interaction was very fast and efficient. The method had a linear response in the concentration ranges of 0.5–8 μM (R2 = 0.9994) and 1–12 μM (R2 = 0.9998) with detection limits of 0.17 and 0.20 μM for CN− and I−, respectively. The sensor was successfully used for the dual detection of both CN− and I− in real water samples with satisfactory results. In conclusion, the specific masking agents in a Hg2+–GQDs system appeared to be good candidates for fluorometric “turn-on” sensors for CN− and I− with excellent selectivity over other ions.