Browsing by Author "K. Uraisin"

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    Determination of trace amounts of bromide by flow injection/stopped-flow detection technique using kinetic-spectrophotometric method
    (2005-12-15) K. Uraisin; D. Nacapricha; S. Lapanantnoppakhun; K. Grudpan; S. Motomizu; Okayama University; Mahidol University; Chiang Mai University
    A simple, sensitive and selective method for the determination of bromide in seawater by using a flow injection/stopped-flow detection technique was examined. The detection system was developed for a new kinetic-spectrophotometric determination of bromide in the presence of chloride matrix without any extraction and/or separation. The detection was based on the kinetic effect of bromide on the oxidation of methylene blue (MB) with hydrogen peroxide in a strongly acidic solution. Large amounts of chloride could enhance the sensitivity of the method as an activator. The decolorisation of the blue color of MB was used for the spectrophotometric determination of bromide at 746 nm. A stopped-flow approach was used to improve the sensitivity of the measurement and provide good linearity of the calibration over the range of 0-3.2 μg ml-1of bromide. The relative standard deviation was 0.74% for the determination of 2.4 μg ml-1bromide (n = 5). The detection limit (3σ) was 0.1 μg ml-1with a sampling frequency of 12 h-1. The influence of potential interfering ions was studied. The proposed method was applied to the determination of bromide in seawater samples and provided satisfactory results. © 2005 Elsevier B.V. All rights reserved.
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    Membraneless vaporization unit for direct analysis of solid sample
    (2007-07-30) K. Sereenonchai; P. Saetear; N. Amornthammarong; K. Uraisin; P. Wilairat; S. Motomizu; D. Nacapricha; Mahidol University; NOAA Atlantic Oceanographic and Meteorological Laboratory; Okayama University
    A new apparatus, called 'membraneless vaporization' (MBL-VP) unit was designed and developed for direct analysis of solid samples. Solid analyte was converted into a gaseous form which then reacts with an indicator reagent. Change in absorbance was used to quantitate the analyte. Stirring with a magnetic bar was employed to facilitate the evaporation of the gas. Unlike the pervaporation technique, hydrophobic membrane was not required for this MBL-VP technique. Application of the membraneless technique for direct determination of calcium carbonate in calcium supplements, has shown to be very precise (R.S.D. = 2.5% for 0.16 mmol CO32-), with detection limit of 0.5 mg CaCO3. Results by this method agreed well with flame atomic absorption spectrometric method. Sample throughput was 20 samples h-1. © 2007 Elsevier B.V. All rights reserved.
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    Simple and selective method for determination of iodide in pharmaceutical products by flow injection analysis using the iodine-starch reaction
    (2004-02-01) D. Nacapricha; K. Uraisin; N. Ratanawimarnwong; K. Grudpan; Mahidol University; The Institute of Science and Technology for Research and Development, Mahidol University; Chiang Mai University
    This work exploited the well-known iodine-starch reaction for development of a simple flow-injection (FI) method for determination of iodide in pharmaceutical samples. Iodide in an injected zone was oxidized to iodine. A gas diffusion unit enables selective permeation of iodine through a hydrophobic membrane. Detection was made very selective for elemental iodine by employing formation of the I3--starch complex. The detection limit (3S/N) of the system was 1mgIL-1. For a liquid patent medicine used for asthma treatment we suggested modification of the system. Direct injection of this sample, which contains a particularly high concentration level of iodide (ca. 9000 mgIL-1), can be achieved by coupling a dialysis unit to the FI system. This has increased the working range to 6000-10,000 mgIL-1without employing complicated nanoliter injection. © Springer-Verlag 2003.
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    Simple flow injection system for colorimetric determination of iodate in iodized salt
    (2002-12-06) N. Choengchan; K. Uraisin; K. Choden; W. Veerasai; Kate Grudpan; D. Nacapricha; Mahidol University; Chiang Mai University
    This work presents a flow injection (FI) system that was developed for determination of iodate. The system utilizes the oxidation of iodide by the analyte to iodine, which subsequently forms tri-iodide. In the presence of starch, the blue I3̄ -starch complex is developed within the sample zone and can be colorimetrically detected at 590 nm. Optimization was carried out to make the system suitable for quantitating iodate added to table salts. To prevent accumulation of the blue complex residue on walls of tubing and the flow cell, a port was placed in the system for injection of 10-3 M thiosulfate plug (100 μl). An injection of this cleaning solution after each sample injection is recommended to avoid positive baseline shift. By means of the paired t-test, the amounts of iodine (mg I kg-1) were statistically compared with the results determined by titration and by iodide ion selective electrode. No significant disagreement at 95% confidence was observed. The proposed system is very simple, uses common chemicals and provides rapid analysis (65 injections per h) with high precision (R.S.D. = 0.66%, n = 10). A detection limit of 2 mg I kg-1salt can be achieved. © 2002 Elsevier Science B.V. All rights reserved.