Solvent mediators with hydrogen bond-forming ability were applied for the construction of biogenic amine-sensitive membrane electrodes by combining them with a lipophilic ion-exchanger, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate. Solvent mediators, such as thiophosphate esters with a P=S group, generally strengthened the response to organic ammonium ions including histamine, and markedly suppressed the responses to inorganic cations, such as Na+ and K+ , suggesting that hydrogen bonding between the NH3+ group of organic ammonium ions and the negatively polarized sulfur atom in the P=S group would enhance such responses. The response to serotonin was especially strengthened in the case of phosphate or thiophosphate esters with a P=O group. The alcoholic solvent mediator, 1-decanol, which has a similar hydrogen bond-forming ability, did not show a pronounced enhancing effect toward organic ammonium ions, while the phenolic mediator p-dodecylphenol exhibited a significantly high degree of selectivity toward histamine. The present results showed that many hydrogen-bonding solvent mediators have the ability to enhance the response to organic ammonium ions, and are thus also suitable for constructing biogenic amine-sensitive electrodes.
Improvement of the operational stability of amperometric sensors based on Prussian Blue (PB) modified glassy carbon electrodes is presented. The long term performance of the sensors was evaluated by injection of hydrogen peroxide (5 µM in potassium buffer) solutions in a flow-injection system during a period of 5 - 10 h. The following parameters were investigated and correlated with the performance of the sensor: the times for electrodeposition and electrochemical activation, temperature, storage time, pH, composition of the buffer solution and of volume sample injected. These analytical characteristics of the modified electrode can be emphasized: initial sensitivity of 0.3 A cm-2 M-1 , detection limit of ca. 0.5 µM, precise results (r.s.d.< 1.5%) and possibility to carry out around 50 samples (50 µL) per hour.
The adsorption of lysozyme from phosphate-buffered saline (pH 7.4) onto bare and cysteine- or 1-octadecanethiol-modified Au electrodes was investigated insitu using an electrochemical quartz-crystal impedance system (EQCIS). The equivalent circuit parameters and resonant frequencies of the piezoelectric quartz-crystal (PQC) resonance, the value of half peak width of the electroacoustic conductance spectrum (DfG1/2) as well as the electrical double-layer capacitance were obtained and analyzed. The adsorption kinetics was analyzed with a scheme of two consecutive reactions occurring at the interface. The amount of adsorbed lysozyme on a hydrophobic surface was greater than that on a hydrophilic one, and a more negative potential brought a larger amount of adsorbed lysozyme. The standard heterogeneous rate constants of ferricyanide/ferrocyanide before and after the lysozyme adsorption were evaluated.
In this paper, we first report the use of powder microelectrodes (PMEs) as the amperometric detector for thiols, hydrazine and hydroxylamine in capillary electrophoresis (CE). This PME, with graphite-supported metalloporphyrin powder as catalyst, offers a few advantages as an amperometric detector in CE. Concentration limit of detection and mass limit of detection obtained for L-cysteine at the PME could reach 88 nM and 230 amol, respectively. The response of thiols at the PME was very reproducible since the electrode fouling was reduced. A relative standard deviation of peak heights (n = 8) of 1.8% and a relative standard deviation of migration time (n = 8) of 1.0% can be obtained for L-cysteine. The material packed in the PME can easily be changed. Hence, it is very convenient to choose suitable catalysts to detect special analytes, and this specially designed microelectrode should be applicable to many other compounds of biological interest.
The rate of formation/extraction of iron(III) with trifluoroacetylacetone in Triton X-100 micellar solution at 298 K was measured by stopped-flow spectrophotometry to identify the route and mechanism of the extraction process. The rate was first order with respect to the metal ion and the extractant in the bulk aqueous phase and inverse first order to the hydrogen ion when the formation of extractable tris-complex was small. The rate obtained under such conditions agreed well with that of complex formation in the single aqueous solution; this suggests that the whole reactions is controlled only by the formation of the mono-complex in the bulk aqueous phase. On the other hand, the rate did not show clear dependencies on the ligand and the hydrogen ion, and was slower than the one expected from the complex formation in the aqueous solution when the formation of the extractable tris-complex was dominant. A slow material transport of the tris-complex from the bulk aqueous phase to the micellar pseudophase was estimated.
In order to learn reasons of the slow formation/extraction rate of iron(III) with trifluoroacetylacetone in Triton X-100 micellar system, the rate of material transport of the extractable tris-complex from the bulk aqueous phase to the micellar pseudophase was investigated at 298 K. The rate was successfully measured using a micellar-concentration-jump stopped-flow technique; the rate was independent of the ligand, the hydrogen ion and the Triton X-100 concentrations of the starting solutions while it was first order with respect to the surfactant concentration of the resulting solutions. The rate of transport was slow enough to reduce the rates of the overall extraction reactions. The rate of formation/extraction in the micellar system was recalculated as if the extraction of the tris-complex was negligibly slow; the corrected rate constant agreed well with that obtained in the aqueous solution. The slow extraction rate observed in the trifluoroacetylacetone-Triton X-100 micellar system was concluded to be due to the slow interfacial transport of the tris-complex.
The stoichiometric protonation constants of some N-substituted amidoximes have been determined potentiometrically in a 50% ethanol-water mixture (v/v) at 25°C and at constant ionic strength. A calculation was peformed using a PC software. The variation of the protonation constants of these compounds was interpreted on the basis of structural effects exposed by the substituents and main skeleton.
This paper enumerates the preparation and characterization of novel temperature-responsive linear polymers comprising N-acryloylamino amide derivatives. The lower critical solution temperature (LCST) at which aggregation starts of a polymer derived from N-acryloyl-L-valine N′-methylamide through telomerization was noted to be less than that of a poly(N-isopropylacrylamide) (PNIPAAm) solution. The alanine derivative critical temperature exceeded that of the valine derivative owing to its smaller hydrophobicity. The thermal transitions of the internal hydrophobicity and solubility were found to be controlled by the N-methylation of the C-terminal amide and that of the N-terminal amide in the polymer. Either process caused a decrease in LCST of the polymers. These findings are discussed from the standpoint of changes in the hydrogen bonding between the amino acid diamide moieties in polymers. Temperature-responsive polymers, such as PNIPAAm, form a hydrophobic environment about their residues, as indicated by a measurement of the internal polarity with a fluorescence probe.
Based on the principle of ligand exchange, a new method for estimating the formation constants of ternary Cu(II) complexes with mixed amino acid enantiomers has been proposed by capillary electrophoresis. As examples, the formation constants of four complexes, namely (L-OH-Pro)Cu(II)(D-Phe), (L-OH-Pro)Cu(II)(L-Phe), (L-OH-Pro)Cu(II)(D-Trp) and (L-OH-Pro)Cu(II)(L-Trp), were estimated by this method. The dependence of stability of complexes on the stereo-selectivity and the possibility of predicting the enantiomer migration order from complex stability has been discussed.
An acidic organophosphorus compound, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPA), has been applied to reversed-phase high-performance liquid chromatography (RP-HPLC). The reversed-phase stationary phase was dynamically modified with EHPA by flowing the mobile phase of an acetone-water mixture containing the extracting reagent. The retention of lanthanoid elements was widely varied by changing the conditions of the mobile phase, i.e., the pH, the EHPA concentration and the acetone content. The selectivity of EHPA is well reflected to the chromatographic systems, and a precise separation of lanthanoid elements was achieved with sufficient resolution. The determination of Sm was examined in the presence of a large amount of Nd. A linear calibration graph was obtained for Sm at the level of 10-7 mol dm-3, in the presence of 1 × 10-4 mol dm-3 of Nd.
By using capillary zone electrophoresis, the human red blood cell population was separated at the single cell level. A single injection of a human blood cell sample gave about one hundred peaks, and most of the peaks could be used to estimate the approximate number of cells. The separation of human red blood cells was also detected by a direct microscopic observation. The injection of a very diluted blood solution gave a few tens of peaks; and the peak heights were almost equal. The peak profile in the electropherogram corresponds directly to the distribution of the electrophoretic mobility of the red blood cells, which reflects on the cell properties, such as the surface charge density, volume and weight. Our finding is the first report to present the fine separation of population of red blood cells at the single cell level.
A new type of capillary gas chromatographic stationary phase containing OH-dibenzo-14-crown-4 (OH-DB14C4) was fabricated by the sol-gel process and coated onto the inner walls of a fused silica capillary. Multiple preparation steps in conventional column technology were avoided. The column demonstrates high column efficiency (>3000 plates m-1), outstanding thermal stability (to 330°C) and a significant ability of deactivation. Compared with a sol-gel OH-terminated silicone oil (OH-TSO) column, the sol-gel OH-DB14C4 column has unique selectivity for the separation of positional isomers of aromatic compounds. In comparison with the dibenzo-propyl-15-crown-5 polysiloxane (PSO-DB-3-15C5) stationary phase, the sol-gel OH-DB14C4 has a high column capacity in separating small-molecular-mass compounds, such as low-molecular-mass alcohols, short-chain fatty acids, and volatile amines. The possible mechanism involved in sol-gel coating with OH-DB14C4 is discussed.
Recoveries of tributyltin and triphenyltin chlorides spiked in fish were improved by addition of 8-quinolinol. Fish samples spiked with tributyltin and triphenyltin chlorides were homogenized with hydrochloric acid. The chlorides were extracted twice into hexane. After centrifugation, a 2-propanol solution of the chlorides were adsorbed to Bondesil SCX and eluted with a methanol solution of 1 M hydrochloric acid. The chlorides were hydradized with an ethanol solution of sodium tetrahydroborate(III) and injected into a gas chromatography-atomic absorption spectrometer. Tributyltin and triphenyltin chlorides in an NIES Certified Reference Material (sea bass) were determined by the proposed procedure. The analytical results were close to the certified and reference values, respectively. Low recoveries were obtained when monobutyltin and dibutyltin chlorides were spiked with and without 8-quinolinol. Tributyltin and triphenyltin chlorides are supposed to form ion-associates with 8-quinolinol in an aqueous solution of hydrochloric acid. The detection limits (three times the signal-to-noise ratio) of tributyltin and triphenyltin chlorides were 105 and 165 pg, respectively.
Cerium(IV) sulfate oxidizes 10-[3′-[N-bis(hydroxyethyl)amino]propyl]-2-chlorophenoxazine [BPCP] reversibly to a pink-colored radical cation [BPCP+·] in the presence of stoichiometric amounts (BPCP:Ce(IV) = 1:1) of the reactants. The radical cation underwent a second one-electron oxidation to form a brownish yellow-colored dication [BPCP2+] in the presence of more than one equivalent of Ce(IV), which was characterized by IR, mass-spectral and UV-vis spectroscopy. The cyclic voltammogram of BPCP exhibited two reversible anodic waves at 640 mV and 1057 mV and two cathodic waves at 582 mV and 930 mV at a scan rate of 24 mV/s. The peak at 640 mV corresponds to the oxidation of BPCP to the radical cation [BPCP+·] and the second anodic peak at 1057 mV stands for the oxidation of the radical cation to dication [BPCP2+]. Bromine oxidized BPCP to three products, as evidenced by HPLC. The tentatively predicted structures based on the mass-spectral data support the formation of brominated oxidized products. The respective first and second formal potentials of BPCP were found to be 782 mV and 936 mV and the transition potential of BPCP in the tritration of ascorbic acid with N-bromosuccinimide was found to be 787 mV in 0.5 M sulfuric acid. The optimum conditions for the use of BPCP as a redox indicator in the macro and micro determination of ascorbic acid, methionine, isoniazid, phenylhydrazine hydrochloride and biotin using N-bromosuccinimide as an oxidant have been developed.
γ-Cyclodextrin dimer linked with ethylenediamine has been synthesized and then modified with dansyl moiety in the presence of N, N′-dicyclohexylcarbodiimide. The sensing ability and binding property of the titled compound are investigated for bile acids. The fluorescence intensity of the cyclodextrin dimer is decreased when a host-guest complex was formed. The value ΔΙ/Ι0 , where Ι and Ι0 are fluorescence intensities in the presence and absence of a guest and ΔΙ is Ι0-Ι, was used as a parameter of sensitivity. This host exhibits highly sensitive and selective molecular recognition ability for ursodeoxycholic acid, lithocholic acid and chenodeoxycholic acid. The behaviors of appended moieties of the host when a host-guest complexation is occurring were studied by induced circular dichroism (ICD) and fluorescence spectra. The ICD spectra patterns of the titled dimer were opposite to those of bis dansyl-modified γ-CyD reported previously. The guest-induced variations in the fluorescence and ICD intensity suggest that the appended moieties work as a hydrophobic cap.
The liquid/liquid extraction of an Al3+-DHAB chelate (DHAB = 2,2′-dihydroxyazobenzen) from water to 1-buthanol (BuOH) in a polymer-based microchannel chip was studied by spatially-resolved fluorescence microspectroscopy. A microchannel (depth, 10 µm; width, 200 µm) was fabricated on a styrol-plastic substrate by an imprinting method. A template for imprinting was prepared by photolithography, in which a spatial pattern printed on a transparency film by a standard drawing software package was used as a photomask. When two immiscible fluids were brought together into the channel chip by pressure-driven flow at the same velocity, a stable parallel stream was observed for each phase without mutual mixing. The extraction of Al-DHAB from water to BuOH was then studied as a fluorescence-intensity profile of the complex in the BuOH phase along the flow direction as well as along the channel-width direction. It was confirmed that extraction proceeded with solution flow and was governed by the contact time between the two phases. The results were explained by a one-dimensional mass-transfer model along the channel-width direction.