Chunpen Thomas
Khon Kaen University
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Featured researches published by Chunpen Thomas.
Talanta | 2014
Siriboon Mukdasai; Chunpen Thomas; Supalax Srijaranai
Dispersive liquid microextraction (DLME) combined with dispersive µ-solid phase extraction (D-µ-SPE) has been developed as a new approach for the extraction of four pyrethroids (tetramethrin, fenpropathrin, deltamethrin and permethrin) prior to the analysis by high performance liquid chromatography (HPLC) with UV detection. 1-Octanol was used as the extraction solvent in DLME. Magnetic nanoparticles (Fe3O4) functionalized with 3-aminopropyl triethoxysilane (APTS) were used as the dispersive in DLME and as the adsorbent in D-µ-SPE. The extracted pyrethroids were separated within 30 min using isocratic elution with acetonitrile:water (72:28). The factors affecting the extraction efficiency were investigated. Under the optimum conditions, the enrichment factors were in the range of 51-108. Linearity was obtained in the range 0.5-400 ng mL(-1) (tetramethrin) and 5-400 ng mL(-1) (fenpropathrin, deltamethrin and permethrin) with the correlation coefficients (R(2)) greater than 0.995. Detection limits were 0.05-2 ng mL(-1) (water samples) and 0.02-2.0 ng g(-1) (vegetable samples). The relative standard deviations of peak area varied from 1.8 to 2.5% (n=10). The extraction recoveries of the four pyrethroids in field water and vegetable samples were 91.7-104.5%. The proposed method has high potential for use as a sensitive method for determination of pyrethroid residues in water and vegetable samples.
Nanoscale Research Letters | 2009
Sujittra Daengsakul; Chunpen Thomas; Ian Thomas; Charusporn Mongkolkachit; Sineenat Siri; Vittaya Amornkitbamrung; Santi Maensiri
This study reports the magnetic and cytotoxicity properties of magnetic nanoparticles of La1−xSrxMnO3(LSMO) withx = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 by a simple thermal decomposition method by using acetate salts of La, Sr, and Mn as starting materials in aqueous solution. To obtain the LSMO nanoparticles, thermal decomposition of the precursor was carried out at the temperatures of 600, 700, 800, and 900 °C for 6 h. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM, and SEM. Structural characterization shows that the prepared particles consist of two phases of LaMnO3(LMO) and LSMO with crystallite sizes ranging from 20 nm to 87 nm. All the prepared samples have a perovskite structure with transformation from cubic to rhombohedral at thermal decomposition temperature higher than 900 °C in LSMO samples ofx ≤ 0.3. Basic magnetic characteristics such as saturated magnetization (MS) and coercive field (HC) were evaluated by vibrating sample magnetometry at room temperature (20 °C). The samples show paramagnetic behavior for all the samples withx = 0 or LMO, and a superparamagnetic behavior for the other samples havingMSvalues of ~20–47 emu/g and theHCvalues of ~10–40 Oe, depending on the crystallite size and thermal decomposition temperature. Cytotoxicity of the synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result shows that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extract of LSMO nanoparticles.
Analytical Methods | 2013
Siriboon Mukdasai; Chunpen Thomas; Supalax Srijaranai
This work reports a sensitive spectrophotometric method for the determination of carbaryl (CBR). The method is based on the extraction of CBR using a two-step microextraction method, dispersive liquid microextraction (DLME) combined with dispersive micro-solid phase extraction (D-μ-SPE) before its detection by spectrophotometry. 1-Octanol was used as the extractant in DLME. For the D-μ-SPE method, magnetic nanoparticles (Fe3O4) functionalized with 3-aminopropyl-triethoxysilane (APTS) were used as the adsorbent to interact with the 1-octanol in DLME. The extracted CBR was spectrophotometrically detected at 480 nm after its derivatization with 2-naphthylamine-1-sulfonic acid (ANSA). The factors affecting the extraction were investigated in detail. The optimal conditions for the DLME were 150 μL of 1-octanol and vortex speed of 3200 rpm for 2 min. For the D-μ-SPE, APTS magnetic nanoparticles (10 mg) was used as the adsorbent, acetonitrile was used as the desorption solvent and the optimum time for desorption was 4 min sonication. The enrichment factor obtained was 2730. The linear range was 10–100 ng mL−1, the limit of detection was 8 ng mL−1, while the limit of quantitation was 26 ng mL−1 and the relative standard deviation was 8.5% from five replicates. The recovery of CBR from three spiked concentration levels of 25, 50 and 75 ng mL−1 was 97.3–108.1%. The method was successfully applied for the determination of CBR in tap water, field water and fruit juice samples. The proposed method has high potential to be used as an efficient preconcentration method for CBR. The APTS magnetic nanoparticles can be reused 10 times with high extraction efficiency.
Magnetic Resonance Imaging | 2013
Petcharakorn Hanpanich; Somchai Pinlaor; Lakhanawan Charoensuk; Puangrat Yongvanit; Chunpen Thomas; Suchart Kothan; Eimorn Mairiang
A 3T MR scanner was used to investigate the relationship between the alteration of bile duct lesions and the hepatic metabolic changes in hamsters infected with Opisthorchis viverrini by using 3T MRI and (1)H MR spectroscopy. Animals were divided into control and infected groups. Five normal hamsters were used as control; fifty-five hamsters were infected with O. viverrini to induce bile duct lesions and hepatic metabolic changes. T2-weighted image sequence in three orthogonal planes were conducted by MRI scans. Single-voxel (1)H MRS was performed to obtain the relative choline-to-lipid ratios. The livers and bile ducts were excised for the histologic examination. The progression of bile duct changes by histology and metabolic changes in O. viverrini infected hamsters were co-investigated. In the O. viverrini-infected group, the T2-weighted images revealed the time-dependent intra- and extra-hepatic duct dilatations in the liver. The mean (±SD) choline-to-lipid ratios were 0.11±0.035 in the control group, whereas the ratio in the infected group increased significantly with the progression of time. Histologic grading of hepatic inflammation and fibrosis were correlated well with the MRI grading (Spearman rank correlation test; r=0.746 and p<0.001). The control group showed no dilatation of the bile ducts and showed normal liver patterns. Noninvasive technique, MRI and (1)H MRS can demonstrated and applied to evaluate not only the inflammation-related fibrosis in the small bile ducts but also the metabolic changes in the liver induced by O. viverrini infection. A significant increase in the choline-to-lipids ratios were observed in parallel with the time-course of infection. O. viverrini infected in human is detected by stool examination. Hepatobiliary morbidity is detected and followed up by ultrasonography. MRI and MRS can be used in conjunction with ultrasonography for evaluation of progression of the disease.
Journal of Physics D | 2007
C Polyon; David John Lurie; Wiwat Youngdee; Chunpen Thomas; Ian Thomas
Theoretical Overhauser-detected EPR spectra of 14 N and 15 N nitroxide systems in low magnetic field by field-cycled dynamic nuclear polarization (FC-DNP) were described by a combination of DNP theory and a model of FC-DNP. Spectra were simulated at magnetic fields between 0 and 8 mT. The simulations were able to predict both the EPR peak positions and their amplitudes, corresponding to those from FC-DNP experiments with 14 N and 15 N TEMPOL solutions. EPR irradiation was in the 45–133 MHz range while NMR signal detection occurred at a field of 59 mT. At this frequency range, four π transitions of a 14 N system and three π transitions of a 15 N system were observed. The simulation programmes were also used to predict the spectral amplitudes of the FC-DNP with EPR irradiation power in the 1–15 W range. Theoretical FC-DNP systems were in good agreement with experimental results; however, at low magnetic fields the inhomogeneity of our magnet system resulted in the EPR peaks being left-shifted and somewhat broader than those from the theoretical prediction.
Journal of Magnetism and Magnetic Materials | 2006
Santi Maensiri; Jakkapon Sreesongmuang; Chunpen Thomas; Jutharatana Klinkaewnarong
Applied Physics A | 2009
Sujittra Daengsakul; Charusporn Mongkolkachit; Chunpen Thomas; Sineenat Siri; Ian Thomas; Vittaya Amornkitbamrung; Santi Maensiri
Applied Physics A | 2013
Santi Phumying; Sarawuth Labuayai; Chunpen Thomas; Vittaya Amornkitbamrung; Ekaphan Swatsitang; Santi Maensiri
Solid State Sciences | 2012
Sujittra Daengsakul; Chunpen Thomas; Charusporn Mongkolkachit; Santi Maensiri
Applied Physics A | 2009
Santi Maensiri; Paveena Laokul; Jutharatana Klinkaewnarong; Chunpen Thomas