Tan, Swee Ngin

From analytical chemistry point-of-view, an ideal sample preparation method should be simple, rapid, automatic, selective, precise, exhaustive, reproducible, and non-degradation to analytes. In this study, a novel sample preparation method, named pressurized matrix solid-phase dispersion (p-MSPD) extraction was developed for simultaneously extracting, separating, purifying, isolating, and analyzing endogenous components in solid sample matrix. Etlingera elatior, a traditional medicine, was applied as a sample matrix to demonstrate the p-MSPD process. The entire extraction, separation, isolation, fractionation and detection were performed automatically with a commercial LC-MS system. The method was satisfactorily applied for the preparation of real samples, and is recommended for quality control of traditional medicines, research efforts when sample amounts are limited, and laboratories that have ordinary LC-MS instrumentation.

In the present work, thermal treatment was used to stabilize municipal solid waste incineration (MSWI) fly ash, which was considered hazardous waste. Toxicity characteristic leaching procedure (TCLP) results indicated that, after the thermal process, the leaching concentrations of Pb, Cu, and Zn decreased from 8.08 to 0.16 mg/L, 0.12 to 0.017 mg/L and 0.39 to 0.1 mg/L, respectively, which well met the limits in GB5085.3-2007 and GB16689-2008. Thermal treatment showed a negative effect on the leachability of Cr with concentrations increasing from 0.1 to 1.28 mg/L; nevertheless, it was still under the limitations. XRD analysis suggested that, after thermal treatments, CaO was newly generated. CaO was a main contribution to higher Cr leaching concentrations owing to the formation of Cr (VI)—compounds such as CaCrO4. SEM/EDS tests revealed that particle adhesion, agglomeration, and grain growth happened during the thermal process and thus diminished the leachability of Pb, Cu, and Zn, but these processes had no significant influence on the leaching of Cr. A microbial assay demonstrated that all thermally treated samples yet possessed strong bactericidal activity according to optical density (OD) test results. Among all samples, the OD value of raw fly ash (RFA) was lowest followed by FA700-10, FA900-10, and FA1100-10 in an increasing order, which indicated that the sequence of the biotoxicity for these samples was RFA > FA700-10 > FA900-10 > FA1100-10. This preliminary study indicated that, apart from TCLP criteria, the biotoxicity assessment was indispensable for evaluating the effect of thermal treatment for MSWI fly ash.

Heavy metal or metalloid contamination is a common problem in soils of urban environments. Their introduction can be due to unpremeditated anthropogenic activities like atmospheric deposition produced by diffuse sources, construction activities and landscape maintenance. Phytoremediation is a rapidly evolving, sustainable approach to remediate the contaminated lands where metals and metalloids are highly persistent in the environment. The present work sets out to determine the level of 12 heavy metals and metalloids (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb and Zn) in soil and their accumulation by plant foliage found in nature parks and industrial sites in Singapore. The latter also involve the investigation of the remediation capacity of selected tropical plant species found at the sampling sites. The study is done using digestion and inductively coupled plasma-optical emission spectrometry. Eleven soil sampling sites across Singapore with 300 sampling points were selected, where soil (0–10 cm) and plant foliage samples were collected. Bioconcentration factors were determined to assess the phytoremediation potential of the collected plant species. Toxicity risk of heavy metals were assessed by comparing the target and intervention values from the soil quality guidelines by the Dutch Standard. Results of the study revealed there were regions where levels of heavy metals and metalloids were relatively high and could affect the environment and the health of flora and fauna in Singapore. Our study discovered that there were available tropical plant species (e.g., wildflowers, ferns and shrubs) which could potentially play a significant role in the remediation of contaminated lands that could open up a huge possibility of developing a sustainable and environmentally-friendly way of managing this emerging urban problem. Results showed that 12 plant species, including hyperaccumulator like Pteris vittata, Centella asiatica, were effective for the accumulation of heavy metals and metalloids.

A practical strategy for the C-N cross-coupling of both aliphatic and aromatic sulfonamides with a variety of substituted aryl bromides is reported. Under the optimized conditions, a good representative of N-arylated products were obtained in good to excellent yields (up to 78 %) under the ligand-free conditions.

An amperometric enzyme electrode for hydrogen peroxide was developed via an easy and effective enzyme immobilization using the sol-gel technique. The enzyme electrode comprises horseradish peroxidase (HRP) immobilized by the silica sol-gel matrix on a carbon paste electrode. Hydrogen peroxide was detected in the presence of ferrocyanide as a mediator to transfer electrons between the electrode surface and hydrogen peroxide. The effect of operational parameters, such as operating potential of the working electrode, mediator concentration, pH, and the thermal stability, were explored for optimum analytical performance by using arnperometric method. A linear calibration curve for hydrogen peroxide measuref!lent was obtained in the range of 2x10-5 to 2.6x10-3 M under the optimized conditions. The apparent Michaelis-Menten constant (¾ app) of the enzyme electrode is 4.8 mM. The performance of this enzyme electrode was also investigated using flow-injection an~ysis (FIA). The enzyme electrode retained about 60% of its activity after 35 days of storage in a phosphate buffer at 4 degree celcius.