Displaying publications 1 - 20 of 137 in total

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  1. Ngeow YW, Williams DR, Chapman AV, Heng JYY
    ACS Omega, 2020 May 12;5(18):10266-10275.
    PMID: 32426583 DOI: 10.1021/acsomega.9b03920
    The reinforcing silica filler, which can be more than 40% of an elastomer composite, plays a key role to achieve the desired mechanical properties in elastomer vulcanizates. However, the highly hydrophilic nature of silica surface causes silica particle aggregation. It remained a challenge for many tire manufacturers when using silica-filled elastomer compounds. Here, the silica surface energy changes when the surface is modified with coupling or noncoupling silanes; coupling silanes can covalently bond the silica to the elastomers. The surface energy of silica was determined using inverse gas chromatography (IGC) at finite dilution (FD-IGC) and found to be reduced by up to 50% when the silica surface was silanized. The spatial distribution of silica aggregates within the tire matrix is determined by transmission electron microscopy (TEM) and a direct correlation between aggregate size (silica microdispersion) and work of cohesion from IGC is reported, highlighting surface energy and work of cohesion being excellent indicators of the degree of dispersion of silica aggregates.
    Matched MeSH terms: Chromatography, Gas
  2. Chai M, Tan G, Lal A
    Anal Sci, 2008 Feb;24(2):273-6.
    PMID: 18270422
    A headspace solid-phase microextraction method has been developed for the determination of 8 pesticides in vegetables and fruits by using gas chromatography with an electron capture detector. Two types of fibers (polyacrylate, 85 microm and polydimethylsiloxane, 100 microm) have been assayed and compared. The main factors: extraction and desorption parameters, ionic strength, and the effects of dilution and organic solvents, were studied and optimized. The optimized procedures resulted in more than 80% recovery for all the investigated vegetable and fruit samples with RSD values below 10%.
    Matched MeSH terms: Chromatography, Gas/methods
  3. Lal A, Tan G, Chai M
    Anal Sci, 2008 Feb;24(2):231-6.
    PMID: 18270414
    A new extraction and cleanup procedure with gas chromatography was developed for the sensitive determination of acephate, dimethoate, malathion, diazinon, quinalphos, chlorpyrifos, profenofos, alpha-endosulfan, beta-endosulfan, chlorothalonil and carbaryl using 1-chloro-4-fluorobenzene as an internal standard in fruits and vegetables. Several extracting and eluting solvents for solid-phase extraction were investigated. The overall extracting solvent with a mixture of acetone:ethyl acetate:hexane (10:80:10, v/v/v) and a eluting solvent of 5% acetone in hexane used with the RPC18 cartridge gave the best recovery for all of the investigated pesticides, and minimized the interference from co-extractants. Under the optimal extraction and clean-up conditions, recoveries of 85 - 99% with RSD < 5.0% (n = 3) for most of the pesticides at the 0.02 - 0.5 mg/kg level were obtained. The limit of detection was between 0.005 - 0.01 mg/kg and the limit of quantification was 0.01 mg/kg. This analytical procedure was characterized with high accuracy and acceptable sensitivity to meet requirements for monitoring pesticides in crops.
    Matched MeSH terms: Chromatography, Gas/instrumentation; Chromatography, Gas/methods
  4. Yassin AA, Mohamed IO, Ibrahim MN, Yusoff MS
    Appl Biochem Biotechnol, 2003 Jul;110(1):45-52.
    PMID: 12909731
    Immobilized PS-C 'Amano' II lipase was used to catalyze the interesterification of palm olein (POo) with 30, 50, and 70% stearic acid in n-hexane at 60 degrees C. The catalytic performance of the immobilized lipase was evaluated by determining the composition change of fatty acyl groups and triacylglycerol (TAG) by gas liquid chromatography and high-performance liquid chromatography, respectively. The interesterification process resulted in the formation of new TAGs, mainly tripalmitin and dipalmitostearin, both of which were absent in the original oil. These changes in TAG composition resulted in an increase in slip melting point, from the original 25.5 degrees C to 36.3, 37.0, and 40.0 degrees C in the modified POo with 30, 50, and 70% stearic acid, respectively. All the reactions attained steady state in about 6 h. This type of work will find great applications in food industries, such as confectionery.
    Matched MeSH terms: Chromatography, Gas
  5. Abd Aziz N, Azlan A, Ismail A, Mohd Alinafiah S, Razman MR
    Biomed Res Int, 2013;2013:284329.
    PMID: 23509703 DOI: 10.1155/2013/284329
    This study was conducted to quantitatively determine the fatty acid contents of 20 species of marine fish and four species of shellfish from Straits of Malacca. Most samples contained fairly high amounts of polyunsaturated fatty acids (PUFAs), especially alpha-linolenic acid (ALA, C18:3 n3), eicosapentaenoic acid (EPA, C20:5 n3), and docosahexaenoic acid (DHA, C22:6 n3). Longtail shad, yellowstripe scad, and moonfish contained significantly higher (P < 0.05) amounts of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA), respectively. Meanwhile, fringescale sardinella, malabar red snapper, black pomfret, Japanese threadfin bream, giant seaperch, and sixbar grouper showed considerably high content (537.2-944.1 mg/100 g wet sample) of desirable omega-3 fatty acids. The polyunsaturated-fatty-acids/saturated-fatty-acids (P/S) ratios for most samples were higher than that of Menhaden oil (P/S = 0.58), a recommended PUFA supplement which may help to lower blood pressure. Yellowstripe scad (highest DHA, ω - 3/ω - 6 = 6.4, P/S = 1.7), moonfish (highest ALA, ω - 3/ω - 6 = 1.9, P/S = 1.0), and longtail shad (highest EPA, ω - 3/ω - 6 = 0.8, P/S = 0.4) were the samples with an outstandingly desirable overall composition of fatty acids. Overall, the marine fish and shellfish from the area contained good composition of fatty acids which offer health benefits and may be used for nutraceutical purposes in the future.
    Matched MeSH terms: Chromatography, Gas
  6. Kwan TK, Lim YT, Gower DB
    Biochem Soc Trans, 1992 May;20(2):232S.
    PMID: 1397603
    Matched MeSH terms: Chromatography, Gas
  7. Kwan TK, Poh CH, Perumal R, Gower DB
    Biochem. Mol. Biol. Int., 1994 Oct;34(4):661-70.
    PMID: 7866291
    The metabolism of varying quantities of pregnenolone has been studied in nuclei-free homogenates from Macaca fascicularis testes by using capillary gas chromatography, after derivatization of metabolites as O-methyl oximes/trimethylsilyl ethers. Evidence was obtained indicating that both pathways for testosterone biosynthesis were operating. 5-Androstene-3 beta, 17 beta-diol was formed in especially high quantities. Two 16-androstenes, namely 5,16-androstadien-3 beta-ol and 5 alpha-androst-16-en-3 beta-ol, were also quantitatively important as metabolites. Co-incubation of stored homogenates with relaxin resulted in 80-100% reduction of the formation of all metabolites quantified except for 5 alpha-androst-16-en-3-one, which was stimulated. Freezing the homogenates at -10 degrees C for 3 weeks resulted in marked 4- to 6-fold reduction in the yields of testosterone and of the 5-ene and 4-ene metabolites from pregnenolone.
    Matched MeSH terms: Chromatography, Gas
  8. Kwan TK, Foong SL, Lim YT, Gower DB
    Biochem. Mol. Biol. Int., 1993 Nov;31(4):733-43.
    PMID: 8298502
    Using the rapid gas chromatographic steroid profiling technique, a number of metabolites of pregnenolone have been separated and quantified after incubation of this steroid with adult rat and neonatal porcine testicular homogenates. It was shown that the 5-ene-3 beta-hydroxy- and the 4-en-3-oxosteroid pathways for androgen biosynthesis were operating in both species, although the former pathway appeared to be more important in porcine testis. This tissue was characterised by the formation of several odorous, and pheromonal, 16-androstenes, which were quantitatively more important than the androgens. Three non-steroidal anti-inflammatory drugs (NSAIDS) caused dose-related inhibition of androgen and 16-androstene biosynthesis when co-incubated with pregnenolone. The order of potency was flurbiprofen > indomethacin > > > aspirin. The possibility that the NSAIDS may interfere with cytochrome P-450 is discussed, since several steroid-transforming enzymes, known to be dependent on this cytochrome for their activity, were markedly inhibited.
    Matched MeSH terms: Chromatography, Gas/methods
  9. Kwan TK, Poh CH, Perumal R, Gower DB
    Biochem. Int., 1988 Nov;17(5):885-94.
    PMID: 3254165
    The metabolism of pregnenolone in subcellular fractions of the testes of the macaque (Macaca fascicularis) has been studied using capillary gas chromatography to characterize and quantify the metabolites, after their conversion into the O-methyloxime and/or trimethylsilyl ether derivatives. The microsomal incubations yielded the greatest quantities of metabolites, with lesser amounts in the mitochondrial fraction. The cytosolic fraction contained no significant quantity of metabolites after incubation, except for 5alpha-androst-16-en-3 beta-ol. This, and other odorous androst-16-enes, found in the microsomal fraction, are of particular interest in the context of animal communication because of their possible pheromonal role. Pregnenolone was converted into androst-5-ene-3 beta,17 beta-diol, androst-4-ene-3,17-dione and testosterone, suggesting that both classical pathways for testosterone synthesis were operating. Testosterone was further converted into 5 alpha-reduced androstanediols, especially in the microsomal fraction.
    Matched MeSH terms: Chromatography, Gas
  10. Kwan TK, Gower DB
    Biochem. Int., 1988 Apr;16(4):629-37.
    PMID: 3390195
    Capillary gas chromatographic 'steroid profiling' has been utilised to separate and quantify the metabolites (derivatized as methyloximes and/or trimethylsilyl ethers) formed from pregnenolone after incubation with rat testicular microsomes. A wide range of steroid metabolites was found, indicating that both the 5-ene and 4-ene pathways of testosterone biosynthesis were operating, as well as 16 alpha-hydroxylation, 20 beta-reduction and the formation of several C19 steroids (the 16-androstenes). At the concentration used, Metyrapone markedly inhibited 16 alpha- and 17-hydroxylation and side-chain cleavage of 17-hydroxylated C21 steroids. 16-Androstene production was also markedly inhibited and the formation of other metabolites was affected to lesser extents. Oxytocin abolished the formation of all C21 and C19 metabolites of pregnenolone.
    Matched MeSH terms: Chromatography, Gas
  11. Kwan TK, Pertiwi AK, Taylor NF, Gower DB
    Biochim. Biophys. Acta, 1988 Sep 23;962(2):214-9.
    PMID: 3167079
    Twenty authentic steroids, derivatized as O-methyl oximes (MO), trimethylsilyl (TMS) ethers or as MO-TMS ethers have been subjected to capillary gas chromatography using two different columns. Virtually all of the steroid derivatives have been resolved, one difficult pair to separate being 5,16-androstadien-3 beta-ol and 5 alpha-androst-16-en-3 beta-ol on the non-selective phase OV-1. Where syn and anti forms of MO derivatives arose, these were also resolved under the conditions utilised. This technique of 'steroid profiling' has been applied to the separation and quantification of metabolites of pregnenolone which were formed during incubations of the microsomal and cytosolic fractions from rat testes. The majority of the metabolites were found in the microsomal incubation. These compounds included some odorous 16-androstenes as well as other C21 and C19 steroids, the formation of which was consistent with the 5-ene and 4-ene pathways of testosterone biosynthesis being operative. In addition, evidence was obtained for 16 alpha-hydroxylation of C21 steroids. Very much less metabolic activity was found in the cytosolic fraction of rat testes. Metabolic pathways have been proposed which both confirm and extend earlier work. We conclude that the rat testis can only form some of the odorous, possibly pheromonal, 16-androstenes and that these are quantitatively less important than in the porcine testis.
    Matched MeSH terms: Chromatography, Gas
  12. Siti Fadhilah Abd. Rahim, Normala Masrom, Muhamad Cyrill Kamal, Noor Azmi Shaharuddin, Khairul Basyar Baharudin, Norliza Abu Bakar
    MyJurnal
    Water contamination by herbicides and chelating agents is increasing mainly due to the
    increasing agricultural activities. Water contamination by these compounds has become a
    concern due to their adverse effects to the environment and humans. Seven sampling sites of
    water sources in Selangor and Johor were chosen for the study. Contamination level of
    Mecoprop (MCCP), Nitrilotriacetic acid (NTA) and Ethylenediaminetetraacetic acid (EDTA) in
    these water body areas was determined by using Gas Chromatography-Electron Capture
    Detector (GC-ECD). Our results indicated that water samples of Sungai Melot in Selangor
    showed the highest presence of EDTA. MCCP was detected at a high level at Sungai Sarang
    Buaya, Johor while NTA showed similar level of concentration at three different sites, Ladang
    10, Ladang Sayur and Mardi, Selangor.
    Matched MeSH terms: Chromatography, Gas
  13. Teo CL, Idris A
    Bioresour Technol, 2014 Dec;174:281-6.
    PMID: 25463809 DOI: 10.1016/j.biortech.2014.10.035
    Nannochloropsis sp. wet biomass was directly transesterified under microwave (MW) irradiation in the presence of methanol and various alkali and acid catalyst. Two different types of direct transesterification (DT) were used; one step and two step transesterification. The biodiesel yield obtained from the MWDT was compared with that obtained using conventional method (lipid extraction followed by transesterification) and water bath heating DT method. Findings revealed that MWDT efficiencies were higher compared to water bath heating DT by at least 14.34% and can achieve a maximum of 43.37% with proper selection of catalysts. The use of combined catalyst (NaOH and H2SO4) increased the yield obtained by 2.3-folds (water bath heating DT) and 2.87-folds (MWDT) compared with the one step single alkaline catalyst respectively. The property of biodiesel produced by MWDT has high lubricating property, good cetane number and short carbon chain FAME's compared with water bath heating DT.
    Matched MeSH terms: Chromatography, Gas
  14. Teo CL, Idris A
    Bioresour Technol, 2014 Nov;171:477-81.
    PMID: 25201293 DOI: 10.1016/j.biortech.2014.08.024
    The types of microalgae strains and the method used in lipid extraction have become crucial factors which influence the productivity of crude oil. In this paper, Nannochloropsis sp. and Tetraselmis sp. were chosen as the strains and four different methods were used to extract the lipids: Hara and Radin, Folch, Chen and Bligh and Dyer. These methods were performed by using conventional heating and microwave irradiation methods. Results revealed that highest lipid yield from the different species was obtained using different extraction methods; both under microwave irradiation. The lipid yield for Tetraselmis sp. and Nannochloropsis sp. was highest when Hara and Radin (8.19%), and Folch (8.47%) methods were used respectively under microwave irradiation. The lipids extracted were then transesterified to biodiesel and the quality of the biodiesel was analyzed using the gas chromatography.
    Matched MeSH terms: Chromatography, Gas
  15. Wong YM, Brigham CJ, Rha C, Sinskey AJ, Sudesh K
    Bioresour Technol, 2012 Oct;121:320-7.
    PMID: 22858502 DOI: 10.1016/j.biortech.2012.07.015
    The potential of plant oils as sole carbon sources for production of P(3HB-co-3HHx) copolymer containing a high 3HHx monomer fraction using the recombinant Cupriavidus necator strain Re2160/pCB113 has been investigated. Various types and concentrations of plant oils were evaluated for efficient conversion of P(3HB-co-3HHx) copolymer. Crude palm kernel oil (CPKO) at a concentration of 2.5 g/L was found to be most suitable for production of copolymer with a 3HHx content of approximately 70 mol%. The time profile of these cells was also examined in order to study the trend of 3HHx monomer incorporation, PHA production and PHA synthase activity. (1)H NMR and (13)C NMR analyses confirmed the presence of P(3HB-co-3HHx) copolymer containing a high 3HHx monomer fraction, in which monomers were not randomly distributed. The results of various characterization analyses revealed that the copolymers containing a high 3HHx monomer fraction demonstrated soft and flexible mechanical properties.
    Matched MeSH terms: Chromatography, Gas
  16. Arifin AA, Don MM, Uzir MH
    Bioresour Technol, 2011 Oct;102(19):9318-20.
    PMID: 21835610 DOI: 10.1016/j.biortech.2011.07.053
    The present work aims to address the gas-phase biotransformation of geraniol into citronellol using growing cells of Saccharomyces cerevisiae (baker's yeast) in a continuous-closed-gas-loop bioreactor (CCGLB). This study revealed that the gaseous geraniol had a severe effect on the production of biomass during the growing cell biotransformation resulting in the decrease in the specific growth rate from 0.07 to 0.05 h⁻¹. The rate of reaction of the growing cell biotransformation was strongly affected by agitation and substrate flow rates. The highest citronellol concentration of 1.18 g/L and initial rate of reaction of 7.06 × 10⁻⁴ g/min g(cell) were obtained at 500 rpm and 8 L/min, respectively.
    Matched MeSH terms: Chromatography, Gas
  17. Khor GK, Sim JH, Kamaruddin AH, Uzir MH
    Bioresour Technol, 2010 Aug;101(16):6558-61.
    PMID: 20363621 DOI: 10.1016/j.biortech.2010.03.047
    In order to characterize enzyme activity and stability corresponding to temperature effects, thermodynamic studies on commercial immobilized lipase have been carried out via enzymatic transesterification. An optimum temperature of 40 degrees C was obtained in the reaction. The decreasing reaction rates beyond the optimum temperature indicated the occurrence of reversible enzyme deactivation. Thermodynamic studies on lipase denaturation exhibited a first-order kinetics pattern, with considerable stability through time shown by the lipase as well. The activation and deactivation energies were 22.15 kJ mol(-1) and 45.18 kJ mol(-1), respectively, implying more energy was required for the irreversible denaturation of the enzyme to occur. At water content of 0.42%, the initial reaction rate and FAME yield displayed optimum values of 3.317 g/L min and 98%, respectively.
    Matched MeSH terms: Chromatography, Gas
  18. Baroutian S, Aroua MK, Raman AA, Sulaiman NM
    Bioresour Technol, 2011 Jan;102(2):1095-102.
    PMID: 20888219 DOI: 10.1016/j.biortech.2010.08.076
    In this study, a novel continuous reactor has been developed to produce high quality methyl esters (biodiesel) from palm oil. A microporous TiO2/Al2O3 membrane was packed with potassium hydroxide catalyst supported on palm shell activated carbon. The central composite design (CCD) of response surface methodology (RSM) was employed to investigate the effects of reaction temperature, catalyst amount and cross flow circulation velocity on the production of biodiesel in the packed bed membrane reactor. The highest conversion of palm oil to biodiesel in the reactor was obtained at 70 °C employing 157.04 g catalyst per unit volume of the reactor and 0.21 cm/s cross flow circulation velocity. The physical and chemical properties of the produced biodiesel were determined and compared with the standard specifications. High quality palm oil biodiesel was produced by combination of heterogeneous alkali transesterification and separation processes in the packed bed membrane reactor.
    Matched MeSH terms: Chromatography, Gas
  19. Yee KF, Lee KT, Ceccato R, Abdullah AZ
    Bioresour Technol, 2011 Mar;102(5):4285-9.
    PMID: 21232947 DOI: 10.1016/j.biortech.2010.12.048
    This study reports the conversion of Jatrophacurcas L. oil to biodiesel catalyzed by sulfated zirconia loaded on alumina catalyst using response surface methodology (RSM), specifically to study the effect of interaction between process variables on the yield of biodiesel. The transesterification process variables studied were reaction temperature, reaction duration, molar ratio of methanol to oil and catalyst loading. Results from this study revealed that individual as well as interaction between variables significantly affect the yield of biodiesel. With this information, it was found that 4h of reaction at 150°C, methanol to oil molar ratio of 9.88 mol/mol and 7.61 wt.% for catalyst loading gave an optimum biodiesel yield of 90.32 wt.%. The fuel properties of Jatropha biodiesel were characterized and it indeed met the specification for biodiesel according to ASTM D6751.
    Matched MeSH terms: Chromatography, Gas
  20. Keng PS, Basri M, Ariff AB, Abdul Rahman MB, Abdul Rahman RN, Salleh AB
    Bioresour Technol, 2008 Sep;99(14):6097-104.
    PMID: 18243690 DOI: 10.1016/j.biortech.2007.12.049
    Lipase-catalyzed production of palm esters by alcoholysis of palm oil with oleyl alcohol in n-hexane was performed in 2L stirred-tank reactor (STR). Investigation on the performance of reactor operation was carried out in batch mode STR with single impeller mounted on the centrally located shaft. Rushton turbine (RT) impellers provide the highest reaction yield (95.8%) at lower agitation speed as compared to AL-hydrofoil (AL-H) and 2-bladed elephant ear (EE) impellers. Homogenous enzyme particles suspension was obtained at 250 rpm by using RT impeller. At higher impeller speed, the shear effect on the enzyme particles caused by agitation has decreased the reaction performance. Palm esters reaction mixture in STR follows Newtons' law due to the linear relation between the shear stress (tau) and shear rate (dupsilon/dy). High stability of Lipozyme RM IM was observed as shown by its ability to be repeatedly used to give high percentage yield (79%) of palm esters even after 15 cycles of reaction. The process was successfully scale-up to 75 L STR (50 L working volume) based on a constant impeller tip speed approach, which gave the yield of 97.2% after 5h reaction time.
    Matched MeSH terms: Chromatography, Gas
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