Sanoe Chairam

Simple flow injection for determination of sulfite by amperometric detection using glassy carbon electrode modified with carbon nanotubes-PDDA-gold nanoparticles.

A new approach is presented for sensitive and selective measurement of sulfite (SO3(2-)) in beverages based on a simple flow injection system with amperometric detection. In this work, the sulfite sensor was a glassy carbon electrode modified with multiwall carbon nanotubes-poly(diallyldimethylammonium chloride)-gold nanoparticles composites (CNTs-PDDA-AuNPs/GC). Electrochemical oxidation of sulfite with this electrode was first studied in 0.1M phosphate buffer (pH 7.0) using cyclic voltammetry. The results indicated that the CNTs-PDDA-AuNPs/GC electrode possesses electrocatalytic activity for the oxidation of sulfite with high sensitivity and selectivity. Sulfite was quantified using amperometric measurement with the new sensor at +0.4V vs Ag/AgCl in conjunction with flow injection. The linear working range for the quantitation of sulfite was 2-200 mg L(-1) (r(2)=0.998) with a detection limit of 0.03 mg L(-1) (3σ of blank) and an estimated precision of 1.5%.The proposed method was successfully applied to the determination of sulfite in fruit juices and wines with a sample throughput of 23 samples per hour.

Enhancing Thai students' learning of chemical kinetics

Chemical kinetics is an extremely important concept for introductory chemistry courses. The literature suggests that instruction in chemical kinetics is often teacher‐dominated at both the secondary school and tertiary levels, and this is the case in Thailand – the educational context for this inquiry. The work reported here seeks to shift students from passive learning to more active, student‐centred learning and involved some 413 first year undergraduate science students in Thailand. Drawing on inquiry‐based learning, the participants were asked to design an experiment investigating the reaction of acids and bases. The research findings suggest that participants were able to explain the changes of the rate of a chemical reaction, and developed good conceptual understanding of chemical kinetics both qualitatively and quantitatively. It also showed this more active teaching approach, which is radically different from normal teaching in Thailand, was an enjoyable experience for the students.

A sensitive and selective on-line amperometric sulfite biosensor using sulfite oxidase immobilized on a magnetite-gold-folate nanocomposite modified carbon-paste electrode

We describe a novel amperometric sulfite biosensor, comprising a carbon-paste electrode (Fe3O4@Au-Cys-FA/CPE) modified with immobilized sulfite oxidase (SOx) on a gold-coated magnetite nanoparticle core, encased within a conjugated folic acid (FA) cysteine (Cys) shell. The biosensor electrode was fabricated using a polydimethylsiloxane (PDMS) and mineral oil mixture as binder, which also enhances the physical stability and sensitivity of the electrode. The developed biosensor displays good electrocatalytic activity toward oxidation of H2O2, which occurs by an enzymatic reaction between SOx and sulfite. The Fe3O4@Au-Cys-FA electrode exhibits good electrocatalytic activity, and has good retention of chemisorbed SOx on the electrode because of its large surface area. Sulfite was quantified using amperometric measurements from the Fe3O4@Au-Cys-FA/CPE biosensor, and using an in-house assembled flow cell at +0.35V (vs. Ag/AgCl), with a phosphate buffer carrier (0.10M, pH 7.0) at a flow rate of 0.8mLmin(-1). The system detects sulfite over the range 0.1-200mgL(-1) (r(2)=0.998), with a detection limit of 10µgL(-1) (3σ of blank). The system exhibits acceptable precision (%R.S.D.=3.1%), rapid sample throughput (109samplesh(-1)), and good stability (2w). The developed biosensor shows satisfactory tolerance to potential interferences, such as sugars, anions, ascorbic acid, and ethanol. We applied the developed method to the determination of sulfite content in wines and pickled food extracts, and our results are in good agreement with those obtained by the standard iodometric method.

Electrocatalytic oxidation of ascorbic acid using a poly(aniline-co-m-ferrocenylaniline) modified glassy carbon electrode.

A poly(aniline-co-m-ferrocenylaniline) was successfully synthesized on a glassy carbon electrode (GCE) by electrochemical copolymerization using a scan potential range from −0.3 to +0.9 V (vs. Ag/AgCl) in 0.5 M H2SO4 containing 30% acetonitrile (ACN), 0.1 M aniline (Ani) and 0.005 M m-ferrocenyaniline (m-FcAni). The field emission scanning electron microscope (FESEM) and electrochemical methods were used to characterize the poly(Ani-co-m-FcAni) modified electrode. The poly(Ani-co-m-FcAni)/GCE exhibited excellent electrocatalytic oxidation of ascorbic acid (AA) in citrate buffer solution (CBS, pH 5.0). The anodic peak potential of AA was shifted from +0.55 V at the bare GCE to +0.25 V at the poly(Ani-co-m-FcAni)/GCE with higher current responses than those seen on the bare GCE. The scan number at the 10th cycle was selected as the maximum scan cycle in electrochemical polymerization. The limit of detection (LOD) was estimated to be 2.0 μM based on the signal-to-noise ratio (S/N = 3). The amperometric responses demonstrated an excellent selectivity for AA determination over glucose (Glu) and dopamine (DA).

Amperometric flow injection analysis of glucose using immobilized glucose oxidase on nano-composite carbon nanotubes-platinum nanoparticles carbon paste electrode ☆

We report a novel amperometric glucose biosensor based on glucose oxidase (GOx) immobilized on a carbon nanotube (CNTs)-poly(diallyldimethyl-ammonium chloride) (PDDA)-platinum nanoparticle (PtNPs) modified carbon-paste electrode (CNTs-PDDA-PtNPs/CPE). The CNTs-PDDA-PtNPs composite materials were characterized by TEM and electrochemical techniques. Cyclic voltammetric results reveal direct electron transfer of the immobilized GOx, indicated by two quasi-reversible redox peaks at a potential of 0.37V (vs. Ag/AgCl) in phosphate buffered solution (PBS) (0.10M, pH 7). The biosensor provides good glucose oxidation activity and retention of GOx electrocatalytic activity due to CNTs-PDDA-PtNPs enhancement of the redox response. The carbon paste electrode was installed as working electrode in a flow through electrochemical cell of a flow injection (FI) system. Glucose was quantified using amperometric measurements at 0.5V vs. Ag/AgCl and PBS carrier (0.10M, pH 7.0) at a flow rate of 1.0mLmin-1. The linear working ranges for glucose measurements were 0.1-3mM (r2=0.995) and 5-100mM (r2=0.997), with corresponding sensitivities of 0.127 and 0.060 (μAs) mM-1, respectively. The system provides good precision of 2.8% R.S.D with a calculated detection limit (3S/N) of 15μM. The proposed method was successfully applied to determination of glucose in food and pharmaceutical samples with throughput of 200 samplesh-1.

Chromatic analysis by monitoring unmodified silver nanoparticles reduction on double layer microfluidic paper-based analytical devices for selective and sensitive determination of mercury(II)

This study demonstrates chromatic analysis based on a simple red green blue (RGB) color model for sensitive and selective determination of mercury(II). The analysis was performed by monitoring the color change of a microfluidic Paper-based Analytical Device (µPAD). The device was fabricated by using alkyl ketene dimer (AKD)-inkjet printing and doped with unmodified silver nanoparticles (AgNPs) which were disintegrated when being exposed to mercury(II). The color intensity was detected by using an apparatus consisting of a digital camera and a homemade light box generating constant light intensity. A progressive increase in color intensity of the tested area on the µPAD (3.0mm) was observed with increasing mercury(II) concentration. The developed system enabled quantification of mercury(II) at low concentration with the detection limit of 0.001mgL(-1) (3 SD blank/slope of the calibration curve) and small sample volume uptake (2µL). The linearity range of the calibration curve in this technique was demonstrated from 0.05 to 7mgL(-1) (r(2)=0.998) with good precision (RSD less than 4.1%). Greater selectivity towards mercury(II) compared with potential interference ions was also observed. Furthermore, the percentage recoveries of spiked water samples were in an acceptable range which was in agreement with the values obtained from the conventional method utilizing cold vapor atomic absorption spectrometer (CVAAS). The proposed technique allows a rapid, simple, sensitive and selective analysis of trace mercury(II) in water samples.

Development of sensitive and selective glucose colorimetric assay using glucose oxidase immobilized on magnetite–gold–folate nanoparticles

We constructed a new nanocomposite catalyst that demonstrated enzyme mimetic activity, like peroxidase, for the colorimetric detection of glucose, using glucose oxidase (GOx) immobilized by glutaraldehyde cross-linking on a gold-coated magnetite nanoparticle (Fe3O4@Au) core, encased within a conjugated cysteine (Cys) folic acid (FA) shell. The synthesized Fe3O4@Au–Cys–FA NPs were characterized using AFM, XRD, DLS and FT-IR analysis. The as-prepared Fe3O4@Au–Cys–FA–GOx nanocomposites were used to catalyze the oxidation of glucose to generate H2O2, coupled with catalyzing the oxidation of a peroxidase substrate, 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)-diammonium salt (ABTS), to ABTS˙+, thereby enabling the colorimetric detection of a colored oxidization product. The proposed nanocomposite exhibits good biocompatibility and provides highly efficient immobilization and retention of GOx. The designed colorimetric method provides a linear dynamic range for glucose detection from 10 μM to 1 mM (r2 = 0.998) and a detection limit of 3.8 μM (3 S.D.blank/slope) with a good reproducibility and the nanocomposite is reusable (≥6 times). Moreover, an interference study revealed that maltose, fructose and sucrose do not affect the colorimetric measurement. The developed method was successfully applied for glucose determination in energy and sports drinks. It is also expected that an expansion of the designed colorimetric method beyond this application may be possible in the future.

Use of a Smartphone as a Colorimetric Analyzer in Paper-based Devices for Sensitive and Selective Determination of Mercury in Water Samples

A smartphone application, called CAnal, was developed as a colorimetric analyzer in paper-based devices for sensitive and selective determination of mercury(II) in water samples. Measurement on the double layer of a microfluidic paper-based analytical device (μPAD) fabricated by alkyl ketene dimer (AKD)-inkjet printing technique with special design doped with unmodified silver nanoparticles (AgNPs) onto the detection zones was performed by monitoring the gray intensity in the blue channel of AgNPs, which disintegrated when exposed to mercury(II) on μPAD. Under the optimized conditions, the developed approach showed high sensitivity, low limit of detection (0.003 mg L-1, 3SD blank/slope of the calibration curve), small sample volume uptake (two times of 2 μL), and short analysis time. The linearity range of this technique ranged from 0.01 to 10 mg L-1 (r2 = 0.993). Furthermore, practical analysis of various water samples was also demonstrated to have acceptable performance that was in agreement with the data from cold vapor atomic absorption spectrophotometry (CV-AAS), a conventional method. The proposed technique allows for a rapid, simple (instant report of the final mercury(II) concentration in water samples via smartphone display), sensitive, selective, and on-site analysis with high sample throughput (48 samples h-1, n = 3) of trace mercury(II) in water samples, which is suitable for end users who are unskilled in analyzing mercury(II) in water samples.

Complexometric and argentometric titrations using thread-based analytical devices

This work describes analytical approaches based on simple complexometric and argentometric titrations leading to the color change of a novel microfluidic thread-based analytical device (µTAD). The device was fabricated from a cotton thread (15 cm) treated with indicator solution, providing an easy-to-use platform for rapid measurement of analyte concentration in aqueous solution. The thread was immobilized onto a support, being a polypropylene sheet or box platform, to facilitate loading of liquid samples. Interaction between the deposited reagents and analytes in the samples then occurred within a few minutes. This resulted in zones of color change with different lengths along the thread depending on the analyte concentration. The interaction zones can be analyzed by human eyes based on comparison of the zone lengths with the printed scales which are correlated with the analyte concentrations. Complexometric titration using µTADs was initially investigated for Mg(II) determination in water and rubber latex samples. These devices consisted of two threads which were pretreated with Eriochrome Black T (EBT) and then treated with ethylenediaminetetraacetic acid (EDTA) in N-cyclohexyl-3-aminopropanesulfonic acid (CAPS) buffer at pH 10. Both threads were tied together with a central knot before being attached to the box platform prior to the analysis. Load of sample solution (6 µL) resulted in the length of red-violet color product on the threads being proportional to the concentration of Mg(II) in waters and rubber latex samples with the working concentration range of 25-1000 mg L-1. In addition, µTAD with a supporting polypropylene sheet consisting of several threads treated with AgNO3 and K2CrO4 indicators was applied for argentometric titration of chloride ion in water and food seasoning samples. After sample loading (3 µL), the initially red-brown threads turned into white corresponding to formation of AgCl(s) on the threads with a working concentration range of 75-600 mg L-1. Greater selectivity towards Mg(II) and chloride compared with potential interference ions was also observed. All the developed μTADs were applied for analysis of real samples which showed results being in agreement with those obtained by classical titrations.

Fostering Active Chemistry Learning in Thailand: Toward a Learner-Centered Student Experiences

Coll, Dahsah, Chairam, and Jansoon state in Chapter 16, that Thailand like many countries worldwide has engaged in major reforms to the science curriculum. A key focus of these reforms has been a shift toward a learner-centered science curriculum. In this chapter, authors report on a number of studies to show how a learner-centered science curriculum in Thailand places major importance on shifting the mindset of Thai students from a rather less active learning role in a strongly teacher-dominated classroom to a role in which they are active learners of chemistry.