Biomedical subjects

Juwadee Shiowatana

Publications and source records attributed to Juwadee Shiowatana.

10 recordsLinked to original sources

PubMed2006

Enhancement effect study of some organic acids on the calcium availability of vegetables: application of the dynamic in vitro simulated gastrointestinal digestion method with continuous-flow dialysis.

The effect of added organic acids on the calcium availability of vegetables was investigated using the dialysis profiles obtained from an in vitro simulated gastrointestinal digestion with continuous-flow dialysis method. Citric acid was the most effective enhancer followed by tartaric, malic, and ascorbic acids. For amaranth, which has a low calcium availability (5.4%), a significant increase of availability was observed with increasing concentrations of all acids studied. With the continuous-flow dialysis approach, organic acids could be observed to promote the dialyzability even at an elevated intestinal pH. An enhancement effect from added organic acids was not clearly observed for Chinese kale, which itself contains a high amount of available calcium (52.9%).

Ascorbic Acid↗

PubMed2006

Development of a simple extraction cell with bi-directional continuous flow coupled on-line to ICP-MS for assessment of elemental associations in solid samples.

A continuous-flow system comprising a novel, custom-built extraction module and hyphenated with inductively coupled plasma-mass spectrometric (ICP-MS) detection is proposed for assessing metal mobilities and geochemical associations in soil compartments as based on using the three step BCR (now the Measurements and Testing Programme of the European Commission) sequential extraction scheme. Employing a peristaltic pump as liquid driver, alternate directional flows of the extractants are used to overcome compression of the solid particles within the extraction unit to ensure a steady partitioning flow rate and thus to maintain constant operationally defined extraction conditions. The proposed flow set-up is proven to allow for trouble-free handling of soil samples up to 1 g and flow rates < or =10 mL min(-1). The miniaturized extraction system was coupled to ICP-MS through a flow injection interface in order to discretely introduce appropriate extract volumes to the detector at a given time and with a given dilution factor. The proposed hyphenated method demonstrates excellent performance for on-line monitoring of major and trace elements (Ca, Mn, Fe, Ni, Pb, Zn and Cd) released when applying the various extracting reagents as addressed in the BCR scheme, that is, 0.11 M CH(3)COOH, 0.1 NH(2)OH.HCl and 30% H(2)O(2), even when a well recognized matrix-sensitive detector, such as ICP-MS, is used. As a result of the enhanced temporal resolution of the ongoing extraction, insights into the breaking down of phases and into the kinetics of the metal release are obtained. With the simultaneous multielement detection capability of ICP-MS, the dynamic fractionation system presents itself as an efficient front-end for evaluation of actual elemental association by interelement comparison of metals leached concurrently during the extraction time. Thus, the intimate elemental association between Cd and Zn in contaminated soils could be assessed.

Chemical Fractionation↗

PubMed2006

Observation of salt-induced beta-lactoglobulin aggregation using sedimentation field-flow fractionation.

Sedimentation field-flow fractionation (SdFFF) was applied in order to characterize particle sizes of beta-lactoglobulin aggregates induced by Ca2+ or Zn2+. Aggregation induced by Zn2+ was faster than that induced by Ca2+. Effects of Zn2+ and beta-lactoglobulin concentrations, as well as contact time, on the aggregation of beta-lactoglobulin were examined. All factors exhibited a combined effect on the size of aggregates, whereby larger aggregates were obtained at increased concentrations of Zn2+ and beta-lactoglobulin. At fixed concentrations of 2% (w/v) beta-lactoglobulin and 10 mM Zn2+, the particle size of the aggregates increased from 0.19 microm (at 15 min) to 0.38 microm (at 2880 min). Further, a hyphenated technique of SdFFF and inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to examine whether intermolecular ionic bridges take part in salt-induced beta-lactoglobulin aggregation. With SdFFF-ICP-OES, protein-cation-protein cross-linkages were observed for beta-lactoglobulin aggregation induced by Zn2+, but not for that induced by Ca2+.

Calcium↗

PubMed2006

Reuse of waste silica as adsorbent for metal removal by iron oxide modification.

Silica gel is widely used in research laboratories, especially for the purification of organic compounds. Consequently, waste silica gel is generated in increasing amounts. In this work, waste silica was modified by coating its surface with iron oxide aiming to obtain an effective adsorbent for metal removal from wastewater. In the preparation of the adsorbent, the optimal pretreatment temperature and iron concentration were investigated. The coated waste silica was characterized for BET surface area, pore size, specific pore volume and iron content. Iron oxide-coated waste silica was tested for the adsorption of Pb(II), Cu(II), Cd(II) and Ni(II) from solutions in a batch system. The effect of contact time, pH and salt concentration on metal adsorption was investigated. It was found that the adsorption of metals occurred rapidly and reached equilibrium within 30 min. The pH suitable for metal adsorption was between 6 and 7 and leaching of iron from the coating was observed only at pH 3 or lower. The presence of salt reduced the adsorption efficiency of the adsorbent. The adsorption behavior followed both Langmuir and Freundlich isotherms (25 degrees C). Finally, the efficacy of the adsorbents was investigated using aqueous lab waste where removal efficiencies ranging from 62 to 89% were achieved when the initial metal concentrations ranged from 13 to 42 mg L(-1).

Adsorption↗

PubMed2006

Iron fractionation for corrosion products from natural gas pipelines by continuous-flow sequential extraction.

The forms and quantities of iron species in corrosion product samples from natural gas pipelines were examined, using a continuous-flow sequential extraction system. Sequential extraction consists of four steps that dissolve water soluble iron (FeSO4), acid soluble iron (FeCO3), reducible iron (Fe-(oxyhydr)oxides) and oxidisable iron (FeS2) fractions, respectively. Selectivity of extracting reagents for particular iron species was evaluated by determination of co-extracted anions, using ion chromatography, and evolved CO2, using indirect flame atomic absorption spectrometer (FAAS). Iron was found predominantly in the reducible fraction (61-99%), indicating that Fe-(oxyhydr)oxides are the major constituents of the corrosion products.

Journal Article↗

PubMed2005

Fractionation and elemental association of Zn, Cd and Pb in soils contaminated by Zn minings using a continuous-flow sequential extraction.

Fractionation and elemental association of Zn, Cd, and Pb in soils near Zn mining areas were studied using a continuous-flow sequential extraction approach. The recently developed sequential extraction procedure not only gave fractional distribution data for evaluation of the mobility or potential environmental impact of the metals, but also the extraction profiles (extractograms) which were used for study of elemental association. In addition, the elemental atomic ratio plot extractogram can be used to demonstrate the degree of anthropogenic contamination. Seventy-nine soil samples were collected in the vicinity of a Zn mine and were fractionated into 4 phases i.e. exchangeable (F1), acid soluble (F2), reducible (F3) and oxidizable (F4) phases. Most samples were contaminated with Zn, Cd and Pb. The reducible phase is the most abundant fraction for Zn and Pb (>50%) while Cd is concentrated in the first 3 extraction steps. The distribution patterns of Cd were obviously affected by soil pH. 55% of Cd appears predominantly in the F1 fraction for acidic soils while in neutral and alkaline soils, it was mostly (70%) found in the F2 + F3 fractions. The extractograms obtained from the continuous-flow extraction system revealed close association between Zn, Cd, Pb and Fe in the acid soluble phase, Cd-Pb and Zn-Fe in the reducible phase for contaminated soils. A correlation study of the 3 metals using a correlation coefficient was also performed to compare the results with the elemental association revealed by the extractograms. Atomic ratio plot extractograms of Zn/Fe, Cd/Fe and Pb/Fe in the reducible phase, where contaminated metals are predominant, can be used to evaluate the degree of anthropogenic contamination. From the elemental atomic ratio plot, it is obvious that the contaminants Cd and Pb are mostly adsorbed on the surface of Fe oxides. Zn, which is present in an approximately 1 ratio 1 ratio with Fe in contaminated soils, does not show a similar trend to that found for Cd and Pb.

Chemical Fractionation↗

PubMed2005

A dynamic continuous-flow dialysis system with on-line electrothermal atomic-absorption spectrometric and pH measurements for in-vitro determination of iron bioavailability by simulated gastrointestinal digestion.

A dynamic continuous-flow dialysis (CFD) method with on-line electrothermal atomic absorption spectrometric (ETAAS) and pH measurements for study of simulated gastrointestinal digestion has been developed for prediction of iron bioavailability. The method used to estimate mineral bioavailability was based on gastric digestion in a batch system then dynamic continuous-flow intestinal digestion. The intestinal digestion was performed in a dialysis bag placed inside a chamber containing a flowing stream of dialyzing solution. Mineral concentration and dialysate pH were monitored by ETAAS and use of a pH meter, respectively. The amount of dialyzed minerals in the intestinal digestion stage was used to evaluate the dialyzability. The dialysis profile and pH change can be used to understand or examine differences between the dialyzability of different food samples. To test the proposed system it was used to estimate the iron dialyzability of different kinds of milk. Iron dialyzability for powdered cow milk, cereal milk, and two brands of soymilk was found to be 1.7, 20.4, 24.9, and 37.7%, respectively. The developed CFD-ETAAS-pH system is a simple, rapid, and inexpensive tool for bioavailability studies, especially for minerals at ultratrace levels.

Animals↗

PubMed2005

Automated sequential injection-microcolumn approach with on-line flame atomic absorption spectrometric detection for implementing metal fractionation schemes of homogeneous and nonhomogeneous solid samples of environmental interest.

An automated sequential injection (SI) system incorporating a dual-conical microcolumn is proposed as a versatile approach for the accommodation of both single and sequential extraction schemes for metal fractionation of solid samples of environmental concern. Coupled to flame atomic absorption spectrometric detection and used for the determination of Cu as a model analyte, the potentials of this novel hyphenated approach are demonstrated by the ability of handling up to a 300 mg sample of a nonhomogeneous sewage amended soil (viz., CRM 483). The three steps of the endorsed Standards, Measurements, and Testing sequential extraction method have been also performed in a dynamic fashion and critically compared with the conventional batchwise protocols. The ecotoxicological relevance of the data provided by both methods with different operationally defined conditions is thoroughly discussed. As compared to traditional batch systems, the developed SI assembly offers minimal risks of sample contamination, the absence of metal re-distribution/readsorption, and dramatic saving of operational times (from 16 h to 40-80 min per partitioning step). It readily facilitates the accurate manipulation of the extracting reagents into the flow network and the minute, well-defined injection of the desired leachate volume into the detector. Moreover, highly time-resolved information on the ongoing extraction is given, which is particularly relevant for monitoring fast leaching kinetics, such as those involving strong chelating agents. On-line and off-line (for Cu, Pb, and Zn) single extraction schemes are also proven to constitute attractive alternatives for fast screening of metal pollution in solid samples and for predicting the current, rather than the potential, element bioavailability by the assessment of the readily mobilizable metal forms.

Journal Article↗

PubMed2005

Field-flow fractionation-inductively coupled plasma mass spectrometry: an alternative approach to investigate metal-humic substances interaction.

Interaction between metal ions and humic matter was investigated using a hyphenated technique, field-flow fractionation-inductively coupled plasma mass spectrometry (FFF-ICP-MS). Aggregation of a metal-spiked commercial Aldrich humic acid in an aqueous solution of calcium ion or in seawater was examined over time intervals of 0-4320 min. The aggregation was demonstrated by shifts in peak maximum of humic matter from smaller size (2.9 nm) to larger size (5.1 or 5.8 nm in Ca2+ solution or in seawater, respectively) and also by the broadening of size distribution profiles. With FFF, size distribution of humic aggregate was characterized. Further, dominant particle size (2.9 nm), mean particle size (3.8 nm), and diffusion coefficient (1.51 x 10(-6) cm2/s) of humic acid solution were determined. With FFF-ICP-MS, associations of Cd, Cu, and Pb with humic aggregates were examined. The mean diameters of Cd-, Cu-, and Pb-bound humic aggregates in the metal-spiked humic acid were 4.1, 4.5, and 5.8 nm, respectively. These diameters were shifted to 6.0, 6.0, and 6.9 nm, respectively, in the humic acid incubated with calcium solution, whereas they were shifted to 6.5, 5.7, and 7.4 nm, respectively, in the humic acid incubated with seawater for three days. Humic aggregate of small size showed more affinity for Cu than Cd and Pb, whereas the large aggregate showed more affinity for Pb than Cd and Cu, respectively.

Environmental Monitoring↗

PubMed2004

Thermodynamic study on the gas chromatographic separation of the enantiomers of aromatic alcohols using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin as a stationary phase.

Gas chromatographic separation of the enantiomers of nineteen structurally related aromatic alcohols was investigated as a function of temperature using a heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin-coated capillary column. Thermodynamic parameters were determined and compared with those obtained with the nonchiral, reference stationary phase, OV-1701. While the -deltaH and -deltaS values for the more retained enantiomers of all nineteen alcohols are comparable on the chiral stationary phase used, the -delta(deltaH) and -delta(deltaS) values are considerably different. Of all the solutes tested, enantiodiscrimination was the greatest for the 2,6-difluoro-alpha-methylbenzyl alcohol.

Alcohols↗