To minimize chemical waste and protect the environment, our team has used green analysis with natural reagents. In this work, we designed a natural-reagent assay kit for iron determination and implemented it in chemistry education in Thailand. The iron assay method was adapted from Thai local wisdom of testing water quality using guava leaves. The guava leaf powder served as a natural reagent in the assay. The kit included equipment, standard and buffer solutions and a manual. A smart device with a built-in camera was used as a detector. Educators in six universities in Thailand implemented the kit in laboratories with modifications depending on their learning outcomes. The kit implementation was evaluated using a survey with questions in four aspects: usability, learning achievement, green chemistry and portability. The high average scores for all questions (> 4.00 of 5.00 points), with the average overall score of 4.53 ± 0.60, indicated satisfaction regarding in all aspects. Using a locally available bio-resource as a natural reagent for green analysis in chemistry education supported sustainable education in Thailand, in terms of quality education (SDG 4) and reduced inequalities (SDG 10) and environmental sustainability (SDG 6—Clean water and sanitation, 12—Responsible consumption and production and 14—Life be-low water).

A new biodegradable platform-based sensor for formaldehyde assay is proposed. Natural rubber latex was modified to polylactic acid–chloroacetated natural rubber polymer blend sheets. The polymer blend sheet was grafted using a water-based system with amine monomers as a platform, with a spot exhibiting positive polarity for immobilizing with anionic dye (Acid Red 27). The sensor was exposed to formaldehyde. The color intensity of the dye on the sensor spot would decrease. Using a smartphone with image processing (via ImageJ program), the color intensity change (∆B) could be followed. A linear calibration, ∆B intensity = 0.365 [FA] + 6.988, R² = 0.997, was obtained for 10–150 mM FA with LOD and LOQ at 3 and 10 mM, respectively (linear regression method). The precision was lower than 20% RSD. Application to real seafood samples was demonstrated. The ready-to-use sensor with the proposed method was cost-effective, was portable for on-site analysis, and demonstrated green chemical analysis.

A monolithic rod of polyurethane foam–[4-(2-pyridylazo) resorcinol] (PUF–PAR) as a simple chemical sensor for lead assays with smartphone detection and image processing was developed. With readily available simple apparatus such as a plastic cup and a stirrer rod, the monolithic PUF rod was synthesized in a glass tube. The monolithic PUF–PAR rod could be directly loaded by standard/sample solution without sample preparation. A one-shot image in G/B value from a profile plot in ImageJ for a sample with triplicate results via a single standard calibration approach was obtained. A linear single standard calibration was: [G/B value] = −0.038[µg Pb²⁺] + 2.827, R² = 0.95 for 10–30 µg Pb²⁺ with a limit of quantitation (LOQ) of 33 µg L⁻¹. The precision was lower than 15% RSD. The proposed method was tested by an assay for Pb²⁺ contents in drinking water samples from Bangkok. The results obtained by the proposed method agree with those of ICP-OES and with 100–120% recovery, demonstrating that the method is useful for screening on-site water monitoring.

Coconut oil as a natural solvent is proposed for green downscaling solvent extractive determination. Determination of Cu(II) using 1,5-Diphenylcarbazide (DPC) was selected as a model for the investigation. Cu(II)-DPC complexes in aqueous solution were transferred into coconut oil phase. The change of the color due to Cu(II)-DPC complexes in coconut oil was followed by using a smartphone and image processing. A single standard concept was used for a series of Cu(II) standard solutions. A downscaling procedure using a 2 mL vial provided a calibration: color intensity = −142 [Cu(II)] + 222, (R² = 0.98), 10% RSD. Using a well plate, a calibration was: color intensity = 61 [Cu(II)] + 68 (R² = 0.91), 15% RSD. Both were for the range of 0–1 ppm Cu(II). Application of the developed procedure to water samples was demonstrated. The developed procedures provided a new approach of green chemical analysis.

A simple flow injection FlameAAS for lead determination with an alginate-polyurethane composite (ALG-PUC) monolithic in-valve column has been developed. The ALG-PUC monolithic rod was prepared by mixing methylene diphenyl diisocyanate with polyol and sodium alginate with the ratio of 2:1:1 by weight for a 5 min polymerization reaction. It was then put into a column (0.8 cm i.d × 11 cm length) situated in a switching valve for the FI set up. A single standard calibration could be obtained by plotting the loaded µg Pb²⁺ vs. FI response (absorbances). The loaded µg Pb²⁺ is calculated: μg Pb²⁺ = FR_load × LT × C_Pb²⁺, where the FR load is the flow rate of the loading analyte solution (mL min⁻¹), LT is the loading time (min), and C_Pb²⁺ is the Pb²⁺ concentration (µg mL⁻¹). A linear calibration equation was obtained: FI response (absorbances) = 0.0018 [µg Pb²⁺] + 0.0032, R² = 0.9927 for 1–150 µg Pb²⁺, and RSD of less than 20% was also obtained. Application of the developed procedure has been demonstrated in real samples.