Showing papers in "Analytical Sciences in 1994"

Chemical Properties of Water-Miscible Solvents Separated by Salting-out and Their Application to Solvent Extraction

Abstract: Fourteen water-miscible polar solvents were investigated for the separation from their aqueous solutions by salting-out using sodium chloride (4mol dm-3). The following solvents showed the phase separation: acetone, acetonitrile, 1, 4- dioxane, tetrahydrofuran, 1-propanol, and 2-propanol. The chemical properties of the separated organic solvents were determined by measuring ET(30)(=1.196×105/λ (kJmol 1)) and DII.I(=1.196×105(λII-1-λI-1)(kJ mol-1))values from the spectral change of 2, 6-Biphenyl-4-(2, 4, 6-triphenylpyridinio)phenolate (DTP) and bis(1, 3-propanediolato)vanadium(IV) (VO(acac)2), where λ, λI, and λII denote the absorption maximum wavelengths (nm) of DTP and VO(acac)2. Solvent properties of acetone, acetonitrile, 1, 4-dioxane, and tetrahydrofuran were dramatically altered by the salting- out. Acceptability of the phase-separated solvents increased due to the dissolution of water molecules having large acceptor numbers. The ion-pair complex of tris(1, 10-phenanthroline)iron(II) chloride was easily extracted into the phase-separated acetonitrile by the salting-out. Some metal chelates of 1-(2-pyridylazo)-2-naphthol (Hpan) and 8- quinolinol (Hox), 5, 10, 15, 20-tetraphenylporphyrin (H2tpp), and ionic species (H2ox+, ox-, and H4tpp2+) were also extracted into 1, 4-dioxane. The raised donor and acceptor abilities of the phase-separated solvents allowed application to solvent extraction.

Immobilization of Dithizone on Surfactant-Coated Alumina for Preconcentration of Metal Ions.

Abstract: In spite of the existence of powerful instrumental determination methods, most trace metal analyses performed to date have required some pretreatment of samples, not only to concentrate the desired trace metals but also to avoid the interferences provided by coexisting elements. 1 3 Ionic or nonionic surfactant molecules form selfaggregates called \"micelles\" above a certain concentration, known as the critical micelle concentration (CMC). The hydrocarbon cores of the micelles give them the unique ability to solubilize many hydrophobic compounds which are otherwise only slightly soluble or insoluble in water. Surfactants can also form aggregates on solid surfaces, which are known as \"hemimicelles\" or \"ad-micelles\" and have solubilization capacities similar to the micelles. For example, surfactant-coated hydrated iron(III) oxide4 or alumina5 have been used for removal of sparingly soluble chemicals (e.g., toluene, p-xylene, trichloroethylene and pentachlorophenol) from aqueous solutions. The literature survey, however, shows that there is no study on the use of these hemi-micelles or ad-micelles for the preconcentration of traces of metal ions. In the present work, a new type of chelate-forming sorbent has been prepared in an aqueous media, based on immobilization of dithizone on surfactant-coated alumina. The sorption and desorption properties were examined to evaluate the sorbent. Copper(II) ions are taken for an example.

Zinc-selective membrane electrode using tetrabutyl thiuram disulfide neutral carrier

Abstract: A poly(vinyl chloride) membrane electrode that is highly sensitive and selective for zinc ions has been developed by using tetrabutyl thiuram disulfide neutral carrier. This electrode incorporated the ionophore along with o-nitrophenyloctyl ether as a plasticizing solvent mediator and potassium tetrakis(p-chlorophenyl)borate as anion excluder; it exhibited a linearity range of 10-1-10-6M with a Nernstian slope of 28.0mV per decade at 25±1°C. The membrane electrode showed a good response to zinc ions in the useful pH range of 3.5 to 6.5, where interferences arise only from a few transition metals such as CuII and PbII.

Bulbed Capillary External Referencing Method Using a Superconducting Magnet NMR Instrument

Abstract: Whether the bulbed capillary external referencing method developed with an electromagnet NMR instrument can be performed also with a superconducting magnet instrument by only changing g cy from 2π/3 to 0 is studied. As the result, the same bulbed capillary and procedures giving high precisions and accuracies are found to be applicable to either electromagnet or superconducting magnet instrument and to either 1 H or even 13 C spectra. Thus, the validity of the generalized bulbed capillary theories and the superiorities of the bulbed capillary method over previous referencing methods are made clear

Flow Injection Chemiluminometric Determination of Folic Acid in Pharmaceutical Formulations

Abstract: A continuous flow chemiluminometric method for determining 10-8 - 10-5M of folic acid in pharmaceutical formulations is described. The method is based on the chemiluminescence (CL) produced by the action of cerium(IV) on folic acid in an acidic medium. The emission intensity is greatly enhanced when Rhodamine B is used as a sensitizer. The procedure is automated, requires no sample pretreatment and solutions can be analyzed at a rate of 180 samples h-1with a relative standard deviation of 0.54% at 1.1×10-5M folic acid (n=10).

Stability of an Agar-Supported Bilayer Lipid Membrane and Its Application to a Chemical Sensor.

Abstract: Lipid membranes made of lecithin and cholesterol were formed by self-assembly in a small aperture on an agar support. The membranes exhibited an average electric resistance of 135GΩ and a capacitance of 0.43μF/cm2. Gramicidin, known to form a channel in uni-lamellar lipid bilayers, reduced the electric resistance to a MΩ level, thus showing the membranes to be of a uni-lamellar bilayer type. The membrane stability was investigated against perturbation with electric potentials and against mechanical agitation in the contacted aqueous solution. About 80% of the membrane preparations remained intact after applying electric potentials of between +1500mV and-1500mV. A similar percentage of the membranes stayed intact under 100rpm magnet stirring in a 30ml vessel. Membranes containing valinomycin responded to K+ ions with changes in both the membrane conductance and the membrane potential.

HPLC/ICP Mass Spectrometric Study of the Selenium Incorporation into Cyanobacterial Metallothionein Induced under Heavy-Metal Stress.

Abstract: Selenium is a toxic element which can cause environmental pollution. Its uptake and incorporation by Zn2+-induced metallothionein (MT) biosynthesis in a cyanobacterium were studied by means of high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometric (ICPMS) detection. When we cultured the cells in selenite-enriched media, as much as 60% of the total selenium in the water-soluble cell components was incorporated into MT, which exists as two major isoforms but occupies a very minor fraction of the overall proteins. Existence of two pathways has been shown for the first time for selenium incorporation into the cyanobacterial MT; one is the S-Se bonding which can be reductively broken by 2-mercaptoethanol, and the other is the formation of selenocysteine followed by its incorporation into the MT peptide chain. No essential difference was noted between selenite and selenate regarding the uptake or the incorporation of Se. The present HPLC/ICPMS system can elucidate biological processes of environmental chemical importance at the molecular level.

Quasi-Elastic Laser Scattering Method for Monitoring Capillary Wave Frequency at a Water/Nitrobenzene Interface

Abstract: A quasi-elastic laser scattering (QELS) method was applied to monitoring the capillary wave frequencies at a water/ nitrobenzene interface. A digital spectrum analyzer was adopted to improve the time resolution of the QELS method. As a result, each power spectrum could be obtained in 1s and saved in an additional 1s. The equipment was checked by monitoring capillary wave frequencies at a water/nitrobenzene interface covered with a monolayer of dipalmitoylphosphatidylcholine (DPPC), i.e. changes of interfacial tension caused by the formation of the monolayer at the interface were detected. The equipment was then applied to a chemical oscillation system. It was found that the interface of the chemical oscillation system was covered with a high density membrane during the chemical oscillation.

6-Methoxy-2-(4-substituted phenyl)benzoxazoles as Fluorescent Chiral Derivatization Reagents for Carboxylic Acid Enantiomers.

Abstract: Three chiral derivatization reagents: 2-[4-(L-leucyl)aminophenyl]-6-methoxybenzoxazole, 2-[4-(D-phenylglycyl)amino-phenyl]-6-methoxybenzoxazole, and 2-[4-(L-phenylalanyl)aminophenyl]-6-methoxybenzoxazole, have been synthesized to permit separation of carboxylic acid enantiomers by high-performance liquid chromatography. Enantiomeric carboxylic acids were readily condensed with the chiral reagents in the presence of 2, 2′-dipyridyl disulfide and triphenylphosphine. The diastereometric amides formed were separated on a normal-phase column, and were sensitively detected fluorometrically at 375nm, with excitation at 330nm. The detection limit of L-PheBOX derivative of 2-phenylpropionic acid was 70fmol at a signal-to-noise ratio of 3.

Simultaneous Determination of Dopamine and Ascorbic Acid with Poly(3-methylthiophene)/Polypyrrole Bilayer-Coated Carbon Fiber Electrodes

Abstract: Poly(3-methylthiophene)/polypyrrole bilayer-coated carbon fiber microcylinder electrodes were prepared by electropolymerization of the respective monomers. The voltammetric characteristics of the electrodes for dopamine (DA) and ascorbic acid (AA) in phosphate buffer saline (PBS) solutions (pH 7.4) were studied. The bilayer-coated electrodes exhibited highly enhanced electrochemical reversibility for the AA oxidation. Quasi-steady-state cyclic voltammograms obtained at 10mV/s had half-wave potentials at-50 and +125mV vs. SCE for AA and DA, respectively, in PBS solution. It has been demonstrated the bilayer-coated electrodes can be used for simultaneous determination of DA and AA in concentrations higher than 3μM and 50μM, respectively, by differential pulse voltammetry.

Development of a Monitoring Tape for Formaldehyde Using Hydroxylamine Sulfate and Methyl Yellow

Abstract: A porous cellulose tape impregnated with a coloring solution that includes hydroxylamine sulfate, Methyl Yellow (pH indicator; pH 2.9-4.0, red-yellow), glycerin and methanol has been developed to provide a highly sensitive means of detecting formaldehyde gas. Formaldehyde reacts with hydroxylamine sulfate to produce sulfuric acid. When a sample including formaldehyde was passed through the tape, the color of the tape changed from yellow to red. Thedegree of color change was proportional to the concentration of formaldehyde at a constant sampling time and flow rate. The degree of color change could be recorded by measuring the intensity of reflecting light (555nm). No interference was observed from carbon monoxide (100ppm), nitrogen monoxide (50ppm), nitrogen dioxide (105ppm), carbon dioxide (4.9%), hydrogen (100%), hydrogen sulfide (32ppm), or hydrogen fluoride (6ppm). The response of acetaldehyde and propionaldehyde were one fortieth and three-hundredths of that of formaldehyde, respectively. Reproducibility tests showed that the relative standard deviation of relative intensity (n=10) was 3.4% for 4ppm formaldehyde. The detection limit was 0.1ppm for formaldehyde at a sampling time of 5min and a flow rate of 400ml/min.

Polymer-Induced Phase Separation in Aqueous Micellar Solutions of Alkylglucosides for Protein Extraction

Abstract: Aqueous micellar solutions of alkylglucosides were separated into two phases at 0°C upon addition of polyethylene glycol 6000 (PEG) or Dextran T-500 (Dextran). One was an aqueous phase in which hydrophilic proteins, cytochrome c and peroxidase (horseradish), were retained, and the other was a surfactant-rich phase into which hydrophobic membrane proteins, bacteriorhodopsin and cytochrome b5, were extracted. A combination of octyl-β-D-thioglucoside (OTG) (or nonyl-β-D-glucoside (NG)) with PEG (or Dextran) was the best choice for extraction of hydrophobic proteins. Extraction yields (50-90%) and concentration factors (7-30) of the hydrophobic proteins were dependent on the types of nonionic surfactants and water-soluble polymers. Solubilization and phase separation in processing cell membranes could be made in a single step at 0°C. Hence the present method would be useful for the purification of thermolabile proteins.

Use of a Small-Bore Internal-Surface Reversed-Phase Silica Column for the Micro High-Performance Frontal Analysis of Carbamazepine in an Albumin Solution with a Small Sample Volume.

Abstract: A micro high-performance frontal analysis (MHPFA) using a small-bore internal-surface reversed-phase silica column (10cm×1.0mm or 1.5mm id.) was developed for the simultaneous determination of the total and unbound carbamazepine (CBZ) concentrations in a human serum albumin (HSA) solution. When a 100-μl or 200-μl portion of a 4-12μg/ml CBZ solution containing 593μM HSA was directly injected into the column, CBZ gave a trapezoidal peakwith the plateau being separated from the HSA peak. The CBZ concentration, calculated from the plateau height, agreed well with the unbound drug concentration determined by the conventional ultrafiltration-HPLC method, and the CBZ concentration calculated from the peak area coincided with the total concentration. The reproducibility was satisfactory (RSD, <3.79%, n=5 or 6). The use of a glass-lined stainless-steel column and an injector-reswitchingtechnique, which prevents the introduction of a diffused portion of the sample solution into the column, was necessary for a frontal analysis using these small-bore columns. The present MHPFA reduced the sample volume to as low as one-seventh of that required for HPFA using an internal-surface reversed-phase silica column of conventional size (15cm×4.6mm i.d.).

Rapid and Selective Sample Preparation for the Chromatographic Determination of Brassinosteroids from Plant Material Using Solid-Phase Extraction Method

Abstract: This report describes a rapid and selective method of sample preparation for the determination of brassinosteroids in samples of biological origin, based on solid-phase extraction. The steroids, brassinolide and castasterone, which possess a C-22,23-diol group, were retained as their cyclic boronates formed on immobilized phenylboronic acid gel in a mixed solvent of pyridine and acetonitrile. After removal of impurities in the sample, parent brassinosteroids could easily be released from their boronates by a mixed solution of hydrogen peroxide and acetonitrile. The phenylboronic acid phase was shown to have a high affinity for brassinosteroids containing a C-22,23-diol. The present method is a first example for the selective extraction of brassinosteroids in a biological sample using immobilized phenylboronic acid gel

Sorption of Sodium Dodecyl Sulfate on Amberlite XAD-2 Resin

Abstract: Among the members of the nonionic macroporous Amberlite XAD series, the styrene-divinylbenzene copolymer XAD-2 and methacrylate-based copolymer XAD-8 have been most commonly used for the preconcentration of aquatic humic substances.'-4 They collect humic and fulvic acids more selectively than macroreticular anion exchangers such as diethylaminoethyl (DEAF)-celluloses and DEAE-Sephadex A-25.6 The desorption recovery, however, is often poor, probably because of the presence of irreversible sorption sites, especially when microgram amounts of humic acid are desorbed from the XAD-2 resin.' Previously, we proposed the use of sodium dodecyl sulfate (SDS) for the enhancement of desorption efficiency.' The function of SDS and its behavior on the resin were not clear, however. The present communication describes the high affinity of SDS for XAD-2. Milligram quantities of SDS were strongly sorbed on the resin over a wide pH range. The distribution of humic acid and SDS in fractions of the column eluate was also studied.

Determination of Isoprenaline with Lucigenin Chemiluminescence Using Flow Injection Analysis.

Abstract: A procedure is presented for determining isoprenaline (10-7-10-4M) in a flow injection system using chemiluminescence detection resulting from the reaction of isoprenaline with 10, 10′-dimethyl-9, 9′-biacridinium dinitrate (lucigenin) in aqueous solution of potassium hydroxide as a carrier stream. The logarithmic calibration curve was linear over the range from 1×10-7M to 1×10-4M. The effects of some analytical conditions on the chemiluminescence yield were investigated. The RSD at 1×10-4M isoprenaline is 0.9% (10 replicates). The method is directly applicable to aqueous solutions of isoprenaline injection (1mg/5ml).

Simple Devices for the Measurements of Absorption Spectra at Liquid-Liquid Interfaces

Abstract: Chemical reactions at liquid-liquid interfaces are an attractive subject in analytical sciences, especially in studies of solvent extraction, liquid membrane separation, counter current chromatography and ionselective liquid membrane electrodes. The role of an interface in the solvent extraction of metal ions was demonstrated in our recent work where we employed a high-speed stirring method to gain advantages of an agitated system, a high specific interfacial area and promotion of mass transfer.l The principle of this method is as follows; when the specific interfacial area is large, interfacial adsorption of a solute can result in a significant decrease of the orgaic phase concentration. This concentration decrease can be measured spectrophotometrically after continuous phase separation by use of a Teflon phase separator.2 This method was applied to measurements of extraction rates as well as to interfacial adsorption in various extraction systems. This is, however, an indirect method with respect to detection of interfacial adsorption. Consequently, a direct spectroscopic approach is desired to identify interfacially adsorbed species. Among the methods proposed for measurements of absorption spectra at liquid-liquid interfaces, the total internal reflection method is thought most informative unless the organic phase contains strongly lightabsorbing species.3 Unfortunately, an organic phase encountered in solvent extraction usually contains colored species, and hence the application of this method is limited. Two methods, an optical stir cell method and a Teflon capillary plate method, are proposed in this work for measurements of interfacial absorption spectra. Both devices were invented based on the same principle as the high-speed stirring method's; an increase in the specific interfacial area enlarges the proportion of the interfacial concentration. These methods were successfully applied to measurements of interfacial spectra of tetraphenylporphyrin (TPP) in a toluene/sulfuric acid system.

A Submersible Flow-through Analyzer for in situ Colorimetric Measurement down to 2000 m Depth in the Ocean.

Abstract: We developed a flow-through chemical analyzer usable in seawater up to a depth of 2000m. The analyzer, which can measure silicate and hydrogen sulfide dissolved in seawater, consists of the following four parts: (i) an acrylic oil-filled vessel containing the flow-through analyzer, (ii) a pressure housing containing electronic circuits (CPU, data logger and drivers to control the analyzer), (iii) a bundle of plastic bags keeping analytical reagents and waste solutions and (iv) batteries for powder supply. Si and H2S are determined colorimetrically using the Molybdenum Blue method and the Methylene Blue method, respectively. After the test operation up to a pressure of 2×107 Pa in a shore-based laboratory, the system was submerged in seawater down to 1200m depth to perform successful in situ Si measurements.

Flow-through Type Chloride Ion Selective Optodes Based on Lipophilic Organometallic Chloride Adducts and a Lipophilic Anionic Dye

Abstract: Flow-through type fiber-optic chloride ion selective optodes have been developed based on chloride adducts of lipophilic organometallic compounds, including a metal: Sn, Ge, Hg or Hf and a lipophilic anionic indicator dye of the diphenyl amine type. The pellicular-type ODS beads were coated with a lipophilic organic liquid containing the lipophilic organometallic compound as the anion-selective ionophore ligand and LAD-3 as the color changeable indicator dye. The optode system was constructed by packing these color changeable ion sensing beads in the flow-through optical cell (cell volume, 7 μl) having a quartz window attached directly to the distal end of a bifurcated optical fiber

Flow-injection spectrophotometric determination of micro amounts of sulfate ion in surface- and sea-water samples with a barium chromate reaction column

Abstract: A rapid and simple flow-injection method using a reaction column packed with barium chromate powder is described for the determination of micro amounts of sulfate ion in surface- and sea-water samples. An aqueous solution containing 4.5mM sodium acetate and 4% ethanol was used as a carrier solution at a flow rate of 0.8ml/min. The absorbance of the chromate ion (which corresponds to the sulfate ion concentration) in the carrier solution from the reaction column was measured using a photometric detector at 370nm. Interference from some cations was eliminated by the use of a cation-exchange resin column installed in front of the reaction column; interference from some anions was reduced by using the carrier solution mentioned above. The concentration range from 0.5 to 5ppm of the sulfate ion in practical water samples can be determined by the proposed method with good reproducibility.

Spectrophotometric Determination of Hydrogen Peroxide Using o-Hydroxyhydroquinonephthalein, Titanium(IV) and Ethylenediaminetetraacetic Acid1

Abstract: We reported2 on a new method for the determination of hydrogen peroxide (denoted by H202) based on a fading of an o-sulfophenylfluorone (denoted by SPF)titanium(IV) complex in the presence of ethylenediaminetetraacetic acid (denoted by EDTA). Although this method is highly sensitive, since the apparent molar absorptivity is 2.3X1051 mol-1 cm', a heating procedure for a long time is necessary for a maximum color development. In a continuation of this investigation of an H2O2 determination, an attempt was made to obtained an o-hydroxyhydroquinonephthalein (denoted by QP)titanium(IV) complex using QP instead of SPF so as to improve the QP-titanium(IV) complex method. This paper deals with a simple and rapid procedure for determination of H202 by utilizing the QP-titanium(IV) complex. The proposed method was applied to an H2O2 determination in rain water. In addition, this method was also applied to assays of glucose and uric acid in human urine by combined use of an appropriate enzyme to produce H2O2 through enzymatic oxidation.

Liquid-Membrane Transport of Gold by a Trioctylamine Mobile Carrier.

Abstract: Liquid-liquid extraction and the membrane transport of gold(III) have been studied using trioctylamine (TOA). Gold(III) was efficiently extracted with TOA from an HCl solution. The extracted AuIII was instantaneously stripped by an HClO4 or HNO3 solution, and subsequently re-extracted at a slow rate. The transport of AuIII was performed across a supported liquid membrane (SLM) impregnated with TOA from an HCl feed solution into an HClO4 product solution. Most of the AuIII was transported with a reasonable enrichment factor, closely corresponding to the feed-to-product volume ratio.

Selective Determination of Oxalate with a Ruthenium(II) Complex/Nafion-Modified Electrode Combined with a Carbon Dioxide Sensor

Abstract: A tris(2,2'-bipyridine)ruthenium(II)/Nafion-modified Pt gauze electrode, where CO 2 was generated by oxidation of substrates, was combined with a CO 2 sensor. The combined sensor responded most effectively to oxalate among the organic acids examined. The response to oxalate was enhanced by use of a doubly-piled, modified Pt gauze electrode. The most suitable applied potential was +0.95 V vs. Ag/AgCl; the stationary response was attained in 10 min after the potential application. The response to 0.5 mM oxalate was reproducible within 3% on 10 repeated runs and remained virtually unchanged over 10 days. The calibration curve for oxalate was linear in the concentration range of 0.1 to 5 mM, and the detection limit was 0.05 mM (S/N=3)

Determination of Trace Amounts of Indium by Graphite-Furnace Atomic Absorption Spectrometry after Preconcentration as the Acetylacetonato Complex on Activated Carbon

Abstract: A rapid and simple preconcentration method by selective adsorption using activated carbon as an adsorbent and acetylacetone as a complexing agent is described for the determination of trace amounts of indium by graphite-furnace atomic absorption spectrometry. The indium-acetylacetonato complex is easily adsorbed onto activated carbon at pH 6.0-8.0. After the activated carbon phase, the adsorbing indium-acetylacetonato complex is separated and dispersed in 5ml of a 2%(v/v) glycerine solution containing 700μg of palladium. The resulting suspension of activated carbon is introduced directly into the graphite-furnace atomizer. The detection limit was 0.025μg/l(s/n=3), and the relative standard deviation was 4.0-5.0% at 1.0μgIn/100ml (n=10). This method was applied to the determination of indium in water samples and proved to be a useful technique for the preconcentration of trace amounts of indium in water samples.

Simple Apparatus for On-Line Chemiluminescence Detection of Proteins Separated by Capillary Zone Electrophoresis.

Abstract: In a capillary zone electrophoretic experiment, Eosine Y (EY) was for the first time found by the authors to comigrate with protein as its complex in a capillary tube containing a phosphate buffer (pH 3.5). This has been successfully utilized for the development of an analytical method based on a combination of capillary zone electrophoresis (CZE) and chemiluminescence (CL) detection.' By this method several proteins could be easily and sensitively estimated. However, the apparatus used in a previous method2,3, in which two streams comprising a buffer solution and a CL reagent solution were included, had the following two problems: (1) a lowering of the CL intensity due to the buffer solution, and (2) difficulty in maintaining steadystate mixing. The authors newly found that a stream of buffer solution is unnecessary since a definite migration current and a good electropherogram were experimentally obtained in the presence of the stationary flow of a fluorosurfactant. This led to the new development of a simple and inexpensive on-line CL detector in which the stream of buffer solution can be eliminated. The former apparatus involved a difficult mechanical operation for preparing a four-way joint; however, the present apparatus can be easily set up using commercially available parts. The detection limit of BSA using EY was improved as follows: 5.0X10-' mol dm 3 (10 fmol) by the former apparatus and 6.0X10.8 mol dm 3 (1.7 fmol) by the present appratus.