Analytical Sciences
Online ISSN : 1348-2246
Print ISSN : 0910-6340
ISSN-L : 0910-6340
Volume 21 , Issue 9
Showing 1-22 articles out of 22 articles from the selected issue
Reviews
  • Wei LI, Zheng CHEN, Yiping LIAO, Huwei LIU
    2005 Volume 21 Issue 9 Pages 1019-1029
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    Traditional Chinese medicines (TCMs) with many unique functions for treating diseases have attracted the interest of people worldwide. They have been popularly utilized for therapy and health promotion in most Asian countries and even in many European and North American countries. However, it should be clearly noted that TCMs are mixtures with complicated composition usually containing hundreds, even thousands of chemically different constituents, and it is the multiple constituents that work synthetically to determine the ultimate effect of a formula of TCM. Meanwhile, some components with toxicity in some TCMs, having various negative effects on different parts of body, may do serious harm to people's health; such harm in particular requires our attention. In this article, applications of different chromatographic and electrophoretic techniques in the analysis of toxic components in TCMs in recent decades have been comprehensively reviewed and some hyphenated procedures (combinations of two kinds of measurement) applied in this field are also summarized.
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Original Papers
  • Bicheng ZHANG, Tao WU, Jimmy C. YU
    2005 Volume 21 Issue 9 Pages 1031-1036
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A technique is described for the determination of total gaseous lead in the atmosphere by honeycomb denuder collection, followed by an electrothermal atomic absorption spectrometry (ETAAS) measurement. The collection efficiency of the honeycomb denuder in which a solution containing 2% HNO3/2% glycerine/1% ammonium dihydrogenphosphate was coated for trapping the gaseous lead in the atmosphere was 98.8%. The linear absorbance response was obtained for a concentration range of 0 - 1.39 µg m-3 of lead in the atmosphere. A precision of 4.8% RSD (peak-height absorbance, n = 11) for an aqueous solution of 1 ng of lead standard, characteristic masses (CM) of 23 pg and detection limit (3 σ) of 54 pg for an aqueous solution of 0.01 ng lead standard was achieved with 100 µg ammonium dihydrogenphosphate as a chemical modifier. The average recovery of lead in three standard samples prepared by the independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 97.8%. The total content of the gaseous lead in the atmosphere of our laboratories was 0.35 - 0.38 µg m-3.
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  • Y. M. ISSA, N. T. ABDEL-GHANI, A. F. SHOUKRY, Howayda M. AHMED
    2005 Volume 21 Issue 9 Pages 1037-1042
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    New chlordiazepoxide hydrochloride (Ch-Cl) ion-selective electrodes (conventional type) based on ion associates, chlordiazepoxidium-phosphomolybdate (I) and chlordiazepoxidium-phosphotungstate (II), were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 60.8 mV per decade of (Ch-Cl) concentration at 25°C for electrodes (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16 × 10-6 - 1 × 10-2 M (Ch-Cl) within the pH range 2.0 - 4.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00139 and 0.00093 V °C-1 for electrodes (I) and (II), respectively. The electrodes showed a very good selectivity for Ch-Cl with respect to the number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of the chlordiazepoxide ion and its pharmaceutical preparation under batch and flow injection conditions. Also, chlordiazepoxide was determined by conductimetric titrations. Graphite, copper and silver coated wires were prepared and characterized as sensors for the drug under investigation.
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  • Hong-Wen GAO, Xiao-Qiao LU, Jiao-Rong REN
    2005 Volume 21 Issue 9 Pages 1043-1049
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    The chromophore, 3-(5-chlor-2-hydroxy-3-sulfophenylazo)-6-(2,4,6-tribromophenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (CSTDD) was used to complex Cu(II) and Co(II) in aqueous solution at pH 9.43. A binuclear complex of Cu-CSTDD-Co was formed and showed a high selectivity for the determination of Co(II). The spectral correction technique was applied to characterize the complexes. The results showed the formation of complexes of Cu(CSTDD), Co(CSTDD)3 and Cu2(CSTDD)2Co. The quantitative analysis of Co(II) at ng/ml level was carried out by the light-absorption ratio variation approach (LARVA). The results showed that the technique is satisfactory to determine Co(II) at trace level in water samples with a detection limit of 2.3 ng/ml.
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  • Hongxia WANG, Junfeng LI, Zhengxia CHEN, Mingyang LIU, Hongyan WANG
    2005 Volume 21 Issue 9 Pages 1051-1055
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A fast and highly efficient Kalman Filter analysis-flow injection chemiluminescence (FI-CL) method was developed to simultaneously determine trace amounts of niobium and tantalum in geological samples. The method, without the boring process of separation and dear instruments, is suitable for field scene analysis. The mixed chemiluminescence kinetic curve was analyzed by a Kalman Filter (KF) in this method to realize the simultaneous determination of niobium and tantalum. Possible interference elements in the determination were investigated. Under the selected conditions, the detection limits (3 σ, n = 11) of niobium(V) and tantalum(V) were 2.1 × 10-3 µg g-1 and 4.0 × 10-3 µg g-1, respectively, and the relative standard deviations were 4.9% and 3.3% (n = 9). The method was applied to the determination of niobium and tantalum in geological samples with satisfactory results.
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  • Han TAO, Wanzhi WEI, Youan MAO, Shufen ZHANG, Jianjun XIA
    2005 Volume 21 Issue 9 Pages 1057-1061
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    Piezoelectric quartz crystal impedance analysis technique was applied to study the chitosanolytic activity of pepsin. The method is based on the viscosity-density reduction of chitosan solution during the enzymatic degradation process. Experiments examined the time courses of the variations of motional resistance (ΔR1) for a quartz crystal. By comparing the ΔR1 response curves under different degradation conditions, the effects of pH, temperature, enzyme and substrate concentration on the chitosanolytic activity of pepsin was investigated in detail. The results suggest that the optimum pH and temperature were 4.6 and 55°C, respectively. Increasing aptly the enzyme or substrate concentration was in favor of the degradation of chitosan. Moreover, the influence of the degree of deacetylation (DD) on the enzymatic degradation was studied. The result indicates that chitosan with a lower DD was easier to be degrade compared with chitosan with a higher DD. Also, it was found that there was a good linear relationship between the ΔR1 response and the DD value. The regression equation was ΔR1 = 0.058 × DD - 6.795 and the correlation coefficient was 0.987.
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  • Mojtaba SHAMSIPUR, Omid Reza HASHEMI, Afsaneh SAFAVI
    2005 Volume 21 Issue 9 Pages 1063-1066
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A rapid flotation method for separation and enrichment of ultra trace amounts of copper(II), cadmium(II), nickel(II) and cobalt(II) ions from water samples is established. At pH 6.5 and with sodium dodecylsulfate used as a foaming reagent, Cu2+, Cd2+, Ni2+ and Co2+ were separated simultaneously with 2-aminocyclopentene-1-dithiocarboxylic acid (ACDA) added to 1 l of aqueous solution. The proposed procedure of preconcentration is applied prior to the determination of these four analytes using inductivity coupled plasma-atomic emission spectrometry (ICP-AES). The effects of pH, concentration of ACDA, applicability of different surfactants and foreign ions on the separation efficiency were investigated. The preconcentration factor of the method is 1000 and the detection limits of copper(II), cadmium(II), nickel(II) and cobalt(II) ions are 0.078, 0.075, 0.072 and 0.080 ng ml-1, respectively.
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  • Behzad REZAEI, Ali Asghar ENSAFI, Siavash NOUROOZI
    2005 Volume 21 Issue 9 Pages 1067-1071
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A simple and sensitive spectrofluorometric method was developed for the simultaneous determination of ascorbic acid and cysteine by a flow-injection system. This method is based on the reduction of Tl(III) with ascorbic acid or cysteine in acidic media, producing fluorescence reagent, TlCl32- (λex = 227 nm, λem = 419 nm). The injected sample solution was divided into two separate streams. The first stream was treated with Tl(III) at pH 3.0 and then passed through a 270 cm reaction coil to the flow cell of the spectrofluorometer, where the fluorescence intensity was measured. This signal is related to ascorbic acid and cysteine concentration. The second part of the injected sample solution was treated with Tl(III) in HCl solution and then passed through a 50 cm reaction coil to the flow cell and the fluorescence intensity was measured. This signal is related only to cysteine. Thus, the ascorbic acid content was determined directly by the difference according to the calibration curve. Ascorbic acid and cysteine can be determined in the range of 1 × 10-6 to 5.0 × 10-5 M, at a rate of 16 samples per hour. The limits of detection (S/N = 3) were 8 × 10-7 M for ascorbic acid and 7 × 10-7 M for cysteine. The influence of potential interfering substances was studied. The proposed method was successfully applied to the simultaneous determination of both analytes in real samples.
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  • Sethsiri S. SAMARATUNGA, Jun NISHIMOTO, Masaaki TABATA
    2005 Volume 21 Issue 9 Pages 1073-1078
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A solvent-extraction system comprising toluene/ter-butanol (ter-BuOH) mixed solvent as the organic phase was developed to selectively extract Cr(VI) from acidic chloride media in the presence of divalent metals, namely Cd(II), Co(II), Cu(II), Ni(II) and Zn(II) under 5 M CaCl2 salting-out conditions. Chromium(VI) was selectively extracted as a solvated ion-pair of [ter-BuOH2+·CrO3Cl-] at ter-BuOH mole fractions of between 0.1 and 0.6 (9.0 - 57.2% in volume). Divalent metals were extracted at ter-BuOH mole fraction over 0.6 with extraction percents of Co(< 20%), Cu(< 15%), Ni(< 10%) and Zn(< 20%). The concentrations of Ca2+, water and ter-BuOH in the organic phase and ter-BuOH in the aqueous phase were determined to find out the effects on the extraction of Cr(VI). The chemical species of Cr(VI) in acidic chloride media containing 5 M CaCl2 and 0.1 M HCl was confirmed to be the CrO3Cl- species. The effects of the acid, salt concentrations in the aqueous phase and the solvent composition of a mixed organic solvent on the extraction of Cr(VI) were evaluated. Based on the above studies, the extraction mechanism was elucidated and the optimum extraction conditions were determined.
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  • M. J. RUEDAS-RAMA, A. RUIZ-MEDINA, A. MOLINA-DÍAZ
    2005 Volume 21 Issue 9 Pages 1079-1084
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A new, sensitive and simple bead injection spectroscopy-flow injection analysis (BIS-FIA) sensor with spectrophotometric detection, using a commercially available flow-cell, is described to the determination of biparametric mixtures. As an analytical model, the metallic mixture Cu(II) and Zn(II) has been chosen. The flow-cell (Hellma 138-OS) is filled by injecting in the flow system 300 µl of a homogeneous bead suspension of an anion exchanger gel (Sephadex QAE A-25) previously loaded with the chromogenic reagent 2-carboxyl-2-hydroxy-5-sulfoformazylbenzene (Zincon). A sequential reaction of Cu(II) and Zn(II) with Zincon to form two complexes is performed on the bead sensing support and the absorbance is monitored at 627 nm, after two successive injections from the mixture solution. The sample containing these metal ions is injected into the first carrier (deionized water, pH 5.9), and Cu(II) selectively reacts with Zincon on the beads, developing the analytical signal. Then, 600 µl of 2 M HCl is injected to decompose the complex, and the carrier solution is changed. At pH 11 (second carrier) both Cu(II) and Zn(II) react with the chromogenic reagent, the absorbance now corresponding to both analytes. The eluent is again injected to descompose both complexes. After three analyses the sensing bead surface is not regenerated. Then, beads are automatically discarded from the flow cell by reversal of the flow, and instantaneously transported out of the system. So the procedure exploits the combination of the concepts of flow-through renewable sensors with Bead Injection Spectroscopy. Using a sample volume of 1000 µl, the calibration graph for Cu(II) is linear over the range 0.05 to 1 µg ml-1 and for Zn(II) from 0.1 to 1.8 µg ml-1 in the presence of each other. RSDs (%) lower than 5% are obtained for both analytes. The sensor is satisfactorily applied to individual determination or mixture resolution in waters, pharmaceuticals, soils and human hair samples.
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  • Masaki MORITA, Yoshie HARADA, Kunihiro ISEKI, Shunsuke IZUMI, Atsunari ...
    2005 Volume 21 Issue 9 Pages 1085-1090
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    We have studied amino acid formation by UV (193 nm) irradiation to organic molecules (amines, alcohols and amides) in aqueous solution. Among several types of detected amino acids, small aliphatic amino acids (Gly and α-, β-Ala and α-, β-, γ-ABA) were quantitatively identified. Among these small aliphatic amino acids, certain amino acids were formed in its free form, even before hydrolysis, contrary to the results of UV irradiation to a gas mixture of CO, NH3, and H2O, where amino acids were hardly detected before hydrolysis. The species distribution of identified amino acids showed a dependence on the starting organic molecules, and also on the presence of ammonia. The formation processes of the identified small aliphatic amino acids were investigated with the aid of electrospray ionization (ESI) MS and MS/MS measurements of photoproducts. Possible formation processes of these amino acid precursors from each starting molecules are proposed. By identifying the amino acid precursor, which has a chiral carbon atom, a new possibility is suggested for asymmetric photosynthesis of amino acid from achiral organic molecules.
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  • Yuji SANO, Kotaro SHIRAI, Naoto TAKAHATA, Takafumi HIRATA, Neil C. STU ...
    2005 Volume 21 Issue 9 Pages 1091-1097
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10 - 20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A ∼4 nA O- primary beam was used to sputter a 5 - 6-µm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500 - 5000 at 10% peak height was attained by an entrance slit set at 40 µm, and each exit slit at 50 µm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5 - 6 µm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to ±38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at <10 µm scale.
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  • Nobuo UEHARA, Sumiko KAWATA, Tokuo SHIMIZU
    2005 Volume 21 Issue 9 Pages 1099-1104
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    The peak shape of tris(2-methyl-8-quinolinolato)gallium(III) by reversed-phase high-performance liquid chromatography was found to be very sensitive to trace amounts of silanol groups on the surface of octadecylsylanized silica gel (ODS silica gel). The variation of the peak of the gallium(III) complex can be used as a probe of the residual silanol groups in an ODS column. The chromatographic peak parameters of the complex were compared with the silanol activities output by some silanol-detecting tests using nitrogen-containing compounds as probes. The comparison was performed with several commercially available ODS columns and laboratory-packed columns in which the amount of silanol groups was controlled by mixing fully endcapped ODS materials and a non-endcapped ODS material. The peak height was the most effective parameter among the peak parameters, and much more sensitive than the silanol-detecting tests using nitrogen-containing compounds, in detecting a trace amount of silanol groups that could not be detected by other silanol-detecting tests.
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  • Chengjie ZHANG, Jun'ichiro MIURA, Yukio NAGAOSA
    2005 Volume 21 Issue 9 Pages 1105-1110
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A sensitive and selective method has been developed for the simultaneous determination of cadmium, zinc, nickel and cobalt. The method is based on the chelation of metal ions with 2-(8-quinolylazo)-4,5-diphenylimidazole (QAI) and the subsequent reversed-phase (RP) high-performance liquid chromatographic separation and spectrophotometric detection of the metal chelates. The chelates were separated on an RP column with acetonitrile-water containing ethylenediamine tetraacetic acid and sodium acetate (pH 7.5). Though Zn(II) and Cd(II) chelates with azo compounds were generally labile in the RP column, these chelates with QAI were successfully detected. When analyses were carried out at 575 nm and at 0.001 absorbance unit full scale, the peak height calibration curves were linear up to 2.0 ng for Cd(II), 2.4 ng for Zn(II), 0.14 ng for Ni(II) and 0.72 ng for Co(II) in 100-µL injections, respectively; the detection limits (3 σ, three times of the standard deviation for the blank signal) for Cd(II), Zn(II), Ni(II) and Co(II) were 4.8, 24, 2.4 and 7.2 pg in 100 µL of injected solution, respectively. The proposed method was successfully applied to the analysis of tobacco without any preliminary concentration or separation.
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  • Shinsaku DOBASHI, Masaharu KIRA, Ryuichiro TANAKA, Yoshinori IZAWA, Yo ...
    2005 Volume 21 Issue 9 Pages 1111-1115
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    This article was retracted. See the Notification.
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Notes
  • Noriyuki KATO, Hiroaki KUBO, Hiroshi HOMMA
    2005 Volume 21 Issue 9 Pages 1117-1119
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A highly-sensitivie analytical method for the detection of p-hydroxymethamphetamine (pOHMA) in urine is presented. The proposed method combines liquid-liquid extraction with acetonitrile and solid-phase extraction by thin-layer chromatography (TLC) with oxidation using potassium hexacyanoferrate(III) and sodium hydroxide to detect the fluorophor of pOHMA. The detection limit for pOHMA is 10 ng (n = 3). The analysis of pOHMA in forensic samples is successfully performed, without interference from endogenous fluorophors, yielding concentrations in the appropriate range for methamphetamine abusers.
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  • Hiroyuki FUJINO, Hideyuki YOSHIDA, Hitoshi NOHTA, Masatoshi YAMAGUCHI
    2005 Volume 21 Issue 9 Pages 1121-1124
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A high-performance liquid-chromatographic method for the determination of acetaminophen in saliva has been developed. This method is based on the precolumn derivatization of acetaminophen with 12-(3,5-dichloro-2,4,6-triazinyl)benzo[d]benzo[1′,2′-6,5]isoindolo[1,2-b][1,3]thiazolidine, a new fluorescence derivatization reagent for phenolic compounds. The resulting derivative of acetaminophen is separated by isocratic elution on a reversed-phase column, and is fluorometrically detected at an emission wavelength of 560 nm with an excitation wavelength of 540 nm. The detection limit (signal-to-noise ratio = 3) was 0.1 µg/mL in saliva. The proposed method permits a highly sensitive and simple determination of acetaminophen in a small amount of saliva without any sample purification.
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  • Woo-Sang LEE, Toshifumi TAKEUCHI
    2005 Volume 21 Issue 9 Pages 1125-1128
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    Bisphenol A (BPA)-recognizing imprinted polymers were synthesized using a template immobilized on silica where the template was grafted to aminopropyl silica. The silica-template conjugate was co-polymerized with a cross-linker (ethylene glycol dimethacrylate) and a functional monomer (4-vinylpyridine or methacrylic acid). The synthesized silica-polymer composites were treated with an aqueous NH4HF2 solution to dissolve the silica matrix. The 4-vinylpyridine-based imprinted polymer showed strong binding affinity to BPA and structurally related compounds having two hydroxyl groups at the 4,4′-position in the bisphenol structure.
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  • Shintaro NOZAWA, Akiko HAKODA, Kenichi SAKAIDA, Tadanao SUZUKI, Akemi ...
    2005 Volume 21 Issue 9 Pages 1129-1132
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    The objective of this collaborative study was to evaluate the proposed method for determining the total nitrogen in soy sauce by the Kjeldahl method submitted to the Codex Alimentarius Commission for endorsement in accordance with the protocol for the design, conduct, and interpretation of method-performance studies. The digestive conditions of the proposed method are the addition of 10 mL of H2SO4, 10 g (8 g by using a block digester) of K2SO4, and 1 mL of 20% CuSO4·5H2O and 80 min boiling period after the liquid is cleared by a heating device. Seventeen laboratories participated, analyzing five soy sauce samples as blind duplicates. Since the volume sampling method used in the JAS (Japanese Agricultural Standard) method showed lower accuracy of data because of the density of soy sauce, the method of sampling by weight was adopted as the proposed method. The total amount of outlier data was within acceptable limits for method-performance studies (≤ 22.2%). Lysine and ammonium sulfate recoveries for all laboratories were ≥ 98% and ≥ 99% respectively. The RSDr (repeatability relative standard deviation) values ranged from 0.4 to 1.3%, and the RSDR (reproducibility relative standard deviation) values were from 0.8 to 1.9%. HORRAT (RSDR/predicted RSDR) for the reproducibility showed 0.2 to 0.4, indicating acceptable precision of the method and excellent analytical performance.
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  • Tariq Mahmood ANSARI, Asad RAZA, Atta-ur REHMAN
    2005 Volume 21 Issue 9 Pages 1133-1135
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    In this study, a simple, fast, accurate and sensitive spectrophotometric method has been developed for the determination of tranexamic acid in bulk and pharmaceutical preparations. The method is based on the reaction of ninhydrin with the primary amino group of tranexamic acid in the basic medium at pH 8.0. The reaction produces a bluish-purple color which absorbs maximally at 565 nm. Beer's law was obeyed in the range of 3 - 40 µg ml-1 with molar absorptivity of 5.093 × 103 L mol-1 cm-1. The effects of various factors such as temperature, heating time, concentration of reagent, color stability and interferences were investigated to optimize the procedure. The results have been validated analytically and statistically. The proposed method has been applied for the determination of tranexamic acid in bulk and pharmaceutical preparations with good results.
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  • Minoru OKUMURA, Sachiko HONDA, Kaoru FUJINAGA, Yasushi SEIKE
    2005 Volume 21 Issue 9 Pages 1137-1140
    Published: 2005
    Released: January 10, 2006
    JOURNALS FREE ACCESS
    A simple and rapid in situ preconcentration method for the spectrophotometric determination of trace ammonia nitrogen in environmental water samples has been developed based on solid-phase extraction using a small column packed with octadecyl group-bonded silica gel (Sep-Pak C18 cartridge). A water sample was taken into a graduated syringe for easy and simple operation and prevention of contamination immediately after sample collection. Ammonia in the sample was reacted with hypochlorite and thymol to be converted into indothymol blue; then the formed indothymol blue was collected as an ion pair between indothymol blue and tetrabutylammonium ion on a Sep-Pak C18 cartridge. The indothymol blue on the cartridge was stable for 4 days. The retained indothymol blue was easily eluted with a mixture of methanol and 0.01 mol/l sodium hydroxide solution. The color intensity due to the indothymol blue was spectrophotometrically measured at 725 nm. The proposed method was successfully applied to environmental water samples such as river water.
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