Charge transfer at a liquid-liquid interface is the key process in a variety of chemical and biochemical processes. The kinetics of electron and proton transfer was investigated at micro- and macroscopic interfaces. Experimentally, these techniques are very distinct due to different approaches in measuring the interfacial potential. Nevertheless, three processes, i.e. generation of charge carriers, diffusion and interfacial transfer, constitute three principal steps of charge separation, and are similar regardless of the dimensionality of the system. Differences in (1) the thickness of the double electric layer, (2) span of the photoreaction zone, and (3) relative rate of electron-transfer and phase-transfer reactions enable approximations which are quite unique for a particular system. The mathematical models, corresponding experimental results, and computer-simulation techniques resulting from various descriptions of charge transfer are discussed.
A system of liquid chromatography combined with inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the determination of rare earth elements (REEs) in geochemical standard reference samples. In liquid chromatography, a strong ion-exchange resin was employed as a stationary phase and ammonium lactate was used as a mobile phase. Multielement detection by ICP-MS was performed in the peak hopping mode to measure the chromatograms for all REEs at the corresponding mass numbers. REEs in the standard rock sample (GSJ JB-1) and the standard sediment sample (Pond Sediment; NIES No.2) were determined by the present measurement system without any correction of the matrix effect and polyatomic ion interferences.
A determination method using an extraction chromatographic resin (EiChroM Sr.Spec™) has been developed for 210 Pb and 210 Po in environmental samples by alpha ray spectrometry. 210 Pb and 210 Po were coprecipitated simultaneously on CuS at pH 4.0 - 5.5. These nuclides were then adsorbed on a Sr.Spec™ resin column (0.79×4.0 cm) in 4 M HCl. The 210 Pb and 210 Po on the resin were eluted with 8 M HCl and 6 M HNO3, respectively. 210 Po was determined by alpha-ray spectrometry after plating on a stainless-steel disk. 210 Pb was determined as 210 Po produced from 210 Pb decay. The method was applied to soil (IAEA-326) and sediments (NIST-4354, IAEA-135, IAEA-368) standard reference materials, and the results agreed with their recommended values. The chemical yield of Po ranged from 56 to 99% and the yield of Pb was 95%. The detection limits of 210 Pb and 210 Po were 0.6 mBq/sample at a counting time of 70000 s.
The effects of preparing molecularly imprinted polymers with 2-hydroxyethyl methacrylate (HEMA) were investigated in detail. Polymers prepared with the addition of HEMA showed better separation than polymers prepared without adding HEMA. Since HEMA effects the hydrophilic properties of polymers and/or the crosslinked polymer network, the imprinted polymers prepared with HEMA should allow good separation of the target molecule.
A simple method has been developed for the voltammetric determination of Ga(III). In a 50 mM Mo(VI)-0.2 M HCl-40%(v/v) CH3CN system, Ga(III) reacts directly with Mo(VI) to form a 12-molybdogallate(III) complex. The yellow Keggin complex undergoes a two-step reduction to the mixed-valence heteropoly-blue species at the glassy carbon (GC) electrode. The 1st voltammetric reduction current depends linearly on the Ga(III) concentration in the range of 5×10-5 - 1×10-3 M. Common metal ions including Al(III) and In(III) at 100-fold concentrations caused no interference. The effect of organic solvents on the formation of the Keggin complexes prepared so far is also discussed.
A novel glassy carbon electrode modified with Malachite Green was investigated. The modified electrode can be used to determine dopamine (DA) and ascorbic acid (AA). The anodic peaks for ascorbic acid and dopamine were separated (ΔEpa about 200 mV) at the poly(malachite green) modified electrode. Thus, DA can be determined in the presence of AA.
The remarkable effect of additive salts on low detection limits as well as slope sensitivities were observed for the response characteristics of bis(crown) and valinomycin based poly(vinyl chloride) (PVC) membrane electrodes. The low detection limits and the slope sensitivities for bis(crown) and valinomycin based PVC membrane electrodes were improved apparently as the hydrophobicity of the additive salts increases. In order to clarify the effect of additive salts of the PVC membrane electrodes, the response characteristics of liquid-membrane based K + and Na + -ISEs, which were fab-ricated by using micro-ion-sensitive field-effect transistors (μ-ISFETs), were evaluated. The low detection limits and the slope sensitivities in the responses of the neutral-carrier based K + and Na + -μ-ISFETs also changed remarkably with the kind as well as the concentration of the additive salts.
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used for the mass determination of the persuccinated derivatives of neutral oligosaccharides. The persuccinated oligosaccharides were derivatized by reacting neutral oligosaccharides with succinic anhydride in pyridine. The analytes were detected mainly as (M+Na) + ions with 100 fmol sensitivity. This method is 10 5 times more sensitive than the direct detection of underivatized oligosaccharides. This new persuccination method can be applied not only to linear oligosaccharides but also to cyclic oligosaccharides which do not have a free hydroxy group at the anomeric site like cyclodextrins. No inorganic reagent is used and no solvent extraction or purification procedure is necessary. So this method is very convenient and efficient for the highly sensitive detection of a variety of oligosaccharides.
A thermospray was modified and used to couple high-performance liquid chromatography (HPLC) to Fourier-transform infrared (FTIR) spectrometry, which was applicable to both normal- and reversed-phase HPLC. Column effluents from the HPLC system were desolvated by thermospray and solutes were deposited as individual spots on a moving stainless-steel belt (0.025 mm thickness×13 mm width) substrate, which continuously transferred the analytes into the diffuse reflectance (DRIFT) accessory of the FTIR, enabling identification of deposited solutes by measurement of the IR spectrum. The thermospray temperature and thermospray height were shown to influence the deposition of solutes. By use of a heated external nitrogen gas flow, desolvation of the reversed-phase HPLC eluents was improved and reduction of power supply in the thermospray capillary was achieved. Thus lower thermospray capillary temperatures could be used. The IR spectra of the separated individual components showed good agreement of the spectral features to those of standard FTIR spectra and no thermal degradation was found to occur.
A flow injection system exploiting pervaporation was developed for spectrophotometric determination of ethanol. It was applied to monitor a molasses fermentation process by real time analysis of sample aliquots taken off from the fermentor unit. Moreover, it was adapted for on-line monitoring. The system yields precise results (RSD <1.5%) at concentrations from 1.00 and 10.0%(v/v) ethanol; Beer’s law is followed (r=0.99946, n=5) and sampling frequency is 20 h -1 . For an on-line determination, controlled standard additions were performed for the proper correction of any matrix effects. Results were compared with those provided by HPLC, and the agreement between them corroborated the applicability of the proposed procedures for large scale analysis and/or for the quality control of molasses fermentation in the sugar-alcohol industry.
Three simple, rapid and accurate titrimetric procedures using potassium dichromate as titrant are described for the determination of six phenothiazine drugs in a pure form and in dosage forms. The procedures are based on the oxidation of phenothiazines in an acid medium to colorless sulfoxides via orange- or purple-colored intermediates. In the first method, phenothiazines are titrated directly in a H2SO4 medium to a colorless end-point. In the second procedure, a known excess of oxidant is added, and after a specified time the residual oxidant is determined iodometrically. The third method employs potentiometric end-point detection. The optimum reaction conditions and other analytical parameters are evaluated and the molar-ratio of the reaction is also calculated. The influence of the substrates commonly employed as excipients with phenothiazine drugs has been studied. A statistical comparison of the results obtained for pure drugs with those of an official method shows excellent agreement and indicates no significant difference in precision.
The adsorption-desorption phenomena of ketones were studied by measuring differential capacity-time curves in a flowing solution. The ketones investigated were acetone, 2-butanone, 3-pentanone and 4-heptanone. The differential capacity-time curves for these ketones showed different shapes with and without peaks. The curves were used to study the adsorption reversibility of the ketones at a mercury electrode. The adsorption of acetone was irreversible and that of 3-pentanone and 4-heptanone was reversible. The adsorption of 2-butanone was rather complicated. It seems that two types of adsorption exist for 2-butanone.