Electrostatic potential is responsible for various phenomena, particularly for the behaviors of ionic species in solution and at various interfaces. In some modes of chromatography, electrostatic interaction often governs overall retention selectivity; ion-exchange chromatography is a typical example. Thus, though the understanding of electrostatic interaction is essential to interpret and predict chromatographic retention in some cases, sufficient attention has not been paid to its roles. There are some possible reasons for this situation: (1) direct estimation of the potential is usually difficult; (2) simple models not involving the contribution from electrostatic potential have given rather good explanations to experimental data. Some research groups have recently attempted to take electrostatic potential effects into consideration in various ways, and have successfully developed chromatographic models. These approaches are expected to facilitate understanding of chromatographic phenomena dominantly controlled by electrostatic interaction and to provide a view of more physical significance. In this review, the author mentions advantages of chromatographic models based on electrostatic theory over usual separated-phase models, and shows problems to be solved.
The toxicity and essential nature of selenium in the environment depend on its concentration and on the chemical forms in which it is present. Dissolved inorganic selenium can be found in natural waters as selenides (Se-II), colloidal elemental selenium (Se0), selenite (SeIV) as well as selenate (SeVI). Organic forms of selenium that may be found in organisms, air or in the aqueous environment are volatile methylselenides, trimethylselenonium ion and selenoamino acids. This review article intends to show some general ideas in speciation analysis of selenium and to highlight some important procedures.
A system for the isotopic measurement of nitrogen at the sub-nanomole level has been developed using a modified noble gas mass spectrometer, allowing 40Ar/36Ar, N2/40Ar, 4He/40Ar and C/N ratios as well as the δ15N value to be measured on one sample. Moreover, carbon dioxide can be collected for a δ13C measurement. The experimental details concerning the analytical system are presented here, including the nitrogen purification procedure and its performance. The analytical errors concerning the δ15N values and 28N2/40Ar ratios were estimated to be about 0.3‰ and 3‰ for actual samples. Using six basalt glasses, the ability of the instrument to make accurate nitrogen isotope measurements has been evaluated. The observed values of the nitrogen content, nitrogen isotopes and nitrogen/argon ratios are compatible with the data in the literature. The results of some basic experiments and the observation of basalt glasses demonstrate that the new system can be applied to measuring nitrogen isotopes in geochemical and environmental samples.
Acid dissociation constants of the hydroxyl groups of sodium hydroxycalixarene-p-sulfonate (18=Na8H4L) were measured by the pH titration method in an aqueous solution. The acid dissociation constants determined were as follows: pKa1=3.73±0.05, pKa2=4.39±0.05, pKa3=8.07±0.02, pKa4=10.1±0.1 under the conditions of μ=0.1 with KNO3 and 25°C. Furthermore, the complex formation reactions of 18 with some divalent metal ions such as Mg2+, Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, and UO22+ (M2+) were investigated by the pH titration method in aqueous solutions and the stability constants of the complexes were evaluated. No complex formation was observed for Cu2+. The slight formation of complexes having a 1:1 molar ratio (M2+:18) was observed for all other divalent metal ions except for UO22+. In contrast, UO22+ formed a relatively stable 2:1 complex in addition to an unstable 1:1 complex. These results indicate that 18 is a highly selective metal ligand for UO22+ among the various divalent metal ions.
The extraction behavior of alkaline, alkaline-earth, and transition metals in liquid-liquid extraction was systematically investigated with a cyclic host compound calixarene carboxyl derivative. Using a novel host ligand, an extraction equilibrium experiment was carried out and the complexation mechanism between the metal ions and the cyclic ligand was investigated. Calixarene carboxyl derivatives showed high extractability for all of the metal ions compared to that of the monomer analog. The extraction behavior of alkaline and alkaline-earth metals is closely related to the cavity size of the cyclic ligands; thus, the tetramer selectively extracted sodium and calcium ions, while the hexamer did so for cesium and barium ions. On the other hand, the extractability of transition metals could not be explained by a size effect, and increased in the order: monomer<tetramer<hexamer. Among transition metals, the higher the stability constant between a metal and the carboxyl group, the more preferential extraction was occurred. These results indicate that the cyclic structure is effective for the extraction of alkaline and alkaline-earth ions, rather than transition-metal ions. All of the metal ions were confirmed to be extracted with the cyclic ligands by forming a 1:1 complex in a toluene phase.
We have found that eutectic compounds of sodium chloride and water form complexes with oxygen, hydrogen sulfide and carbon dioxide in the aqueous 0.1 M NaCl solution. The oxygen complex differentiates between the enantiomeric isomers of amino acids and sugars. The direction of this differentiation agrees with that of biological systems in nature where only the L-isomers of amino acids are used to form proteins, while D-form sugars form polysaccharides. These results represent the first complete differentiation of enantiomeric isomers in an inorganic system, and were achieved without the aid of any in vivo biomaterials, such as enzymes. Other alkali chlorides were also examined. The eutectic compound of potassium chloride and water forms a similar oxygen complex which also differentiates the isomers of amino acids and sugars. However, the direction of this differentiation is opposite that in the case of sodium chloride. These results call for the special attention to the fact that the concentration of potassium ions in living cells is higher than that of sodium ions. The mechanism of these observations is not yet clear, but is likely to involve the structure of an aqueous solution of a specific concentration (0.1 M) of salt. The effects of various gases were also examined. Like oxygen, hydrogen sulfide also forms a complex with the eutectic compound of sodium chloride and water. This complex differentiates the isomers of amino acids and sugars in a similar manner to the way the oxygen complex dose. This finding suggests that the enantiomeric isomers of amino acids and sugars could be differentiated in an inorganic environment. Carbon dioxide also forms a complex with the eutectic compound of sodium chloride and water, but does not differentiate the isomers.
Some of the ion-exchange resins modified with metalloporphyrins have been found to exhibit glutathione-peroxidase (GSHPx)-like catalytic activities for hydrogen peroxide and cumene hydroperoxide in the oxidative reaction of glutathione to disulfide. In particular, the anion-exchange resin modified with Mn(III)-tetrakis(sulfophenyl)porphine (Mn-TSPPr) exhibited stronger activity than GSHPx, and hence Mn-TSPPr was expected to be a good mimesis in place of GSHPx or immobilized GSHPx for the determination of peroxide.
The present flow analysis of hydrogen peroxide is based on a measurement of the absorbance of quinoid-dye formed by a following reaction (1) using an anion-exchange resin modified with manganese(III)-tetrakis(sulfophenyl)porphine (Mn-TSPPr), which catalyzes the reaction (1), just like an immobilized peroxidase: 4-aminoantipyrine+4-chlorophenol+2H2O2 →Mn-TSPPr quinoid dye+4H2O [reaction (1)]. Mn-TSPPr is more advantageous than immobilized peroxidase in terms of storage and stability for both temperature and moisture. The present facilitated method is satisfactory in reproducibility and sensitivity.
A rapid and simple preconcentration method based on the combined use of ammonium pyrrolidinedithiocarbamate (APDC) and a finely divided anion-exchange resin has been described for the determination of trace amounts of cadmium and lead by graphite-furnace atomic absorption spectrometry (GFAAS). Cadmium- and lead-APDC complexes were extracted simultaneously on the resin at pH 6. The resin particles holding the cadmium- and lead-APDC complexes were separated by filtration and dispersed in 1.0 ml of 0.1 mol l-1 hydrochloric acid containing 100 μg of palladium(II). The resulting suspension was introduced directly into the graphite furnace by an automatic sampler. The detection limits of cadmium and lead in a 150-ml sample aliquot were 0.17 and 5.7 ng l-1, respectively, based on three-times the standard deviation of blank values. The proposed method was applied to the determination of nanograms per liter levels of cadmium and lead in tap water.
A dynamically coated column of C18-bonded silica gel with methyltricaprylylammonium chloride was used for the selective preconcentration of Cd from water samples under acidic conditions. The complete adsorption of Cd occurred from seawater with no additional reagent, and was found from non-saline waters containing 0.05 - 5 M HCl. The interfering matrix ions were not retained and pass through the column. The sorbed Cd was eluted with 4 ml of 0.1 M HNO3 for a subsequent measurement by graphite-furnace AAS. The technique has been successfully applied to seawater and riverwater certified reference materials. The preconcentration process is simple and minimizes the contamination of blanks. The detection limit (3 σ) is 0.2 ng l-1 of Cd based on a 75-fold preconcentration.
We have fabricated composite films of polypyrrole/quinone sulfonate via electropolymerization. The FTIR investigation indicated the incorporation of quinone sulfonate in the polypyrrole (PPy) film to compensate for a positive charge in the polymer chain. Further, the elemental analysis of PPy/9,10-anthraquinone-2-sulfonate (AQS-) showed that 0.29 of the sulfonate was incorporated per pyrrole unit. Cyclic voltammetric results in dimethylsulfoxide and dimethylformamide solutions showed that the two 1-electron transfer steps could be assigned to the formation of radical dianion (AQS2-.) and trianion (AQS3-). The positive shift of the first cathodic peak for the incorporated AQS- indicated a strong interaction between the dianion and the cationic sites of the polymer. The PPy/AQS- film worked as a cation-exchanger at electrode potentials below about -0.3 V vs. Ag/AgCl (saturated KCl) because of the creation of the anionic sites of the reduced quinone.
Organosilicon polymers have attracted considerable attention as a new class of functional polymers of the next generation because of their unique electronic and optical properties originating from the delocalization of σ-σ* conjugated electrons along the Si-Si main chain of polysilane. Thus, for these polymers, oxygen is the most remarkable impurity. Nevertheless, the determination of oxygen in any organic material is extremely difficult. Especially, for oraganosilicon compounds, conventional methods do not give good results. In this study we investigated the reason for the low recoveries of organosilicon compounds by several kinds of determination methods, and developed a new determination method involving on inert-gas fusion equipped converter, which includes platinum-carbon. According to our method, oxygen in organosilicon polymers can be determined quantitatively. We confirmed that our new method is applicable not only to organosilicon materials, but also to organic and organometallic compounds as well as inorganic materials.
A new optic-fiber sensor for metronidazole (1-(2-hydroxyethyl)-2-methyl-5-nitromidazole) has been fabricated with a fluorescent copolymer prepared from 3-hydroxy-4′-N,N-dimethylaminoflavone methacrylate, methyl methacrylate, and butyl acrylate (PFMB). The sensing is based on the quenching of the fluorescence of a PFMB membrane by metronidazole. An orthogonal-experimental design was used for the membrane composition optimization. The present sensor responds linearly to metronidazole in the concentration range of 3.00×10-5 mol l-1 to 3.00×10-3 mol l-1 with a detection limit of 1.00×10-5 mol l-1. The response is on the order of 30 s. The lifetime is enhanced by covalently immobilizing the flavone derivative to the membrane, which hinders leaching of the dye from the membrane. With the described sensor, good reproducibility and reversibility have been realized. The sensor has also shown good selectivity over common inorganic anions and cations, and some pharmaceuticals. It can be used for the direct determination of metronidazole in commercial pharmaceutical preparations; the obtained results were in agreement with those obtained by a pharmacopoeia method.
A novel FIA system for CO2 was constructed and compared with a N,N,N′,N′-tetrakis-2-hydroxylethyl ethylenediamine(THEED)-coated quartz crystal microbalance (QCM) for the determination of CO2 in wine and beer samples. This FIA method is based on the use of a gas-permeable membrane to separate CO2 from a carrier stream of 0.5 mol/l phosphate buffer (pH 6.0) into a recipient stream of 10 mmol/l tris(hydroxymethylamino)methane (Tris) containing 1.0 mmol/l KCl and a piezoelectric impedance sensor to follow the conductance change occurring in the acceptor solution. Although the results for real samples obtained by the FIA, the QCM and the conventional titrimetric methods, respectively, agree well with each other, the FIA method offers the best precision. The FIA method is also characterized by its high throughput, promising sensitivity, excellent selectivity, low cost and easy manipulation, etc. The influence of some experimental parameters on the FIA’s performance is discussed in detail.
A flow injection method based on the catalytic action of iodide on the color-fading reaction of the FeSCN2+ complex was proposed and applied to the determination of iodine in milk. At pH 5.0, temperature 32°C and measurements at 460 nm, the decrease in absorbancy of Fe3+-SCN (0.10 and 0.0020 mol l-1) in the presence of NO2- (0.3 mol l-1) is proportional to the concentration of iodide, with linear response up to 100.0 μg I- l-1. The detection limit was determined as 0.99 μg I- l-1 (3σ blank/slope); and the system handles 48 samples h-1. Organic matter was destroyed by a dry procedure carried out under alkaline conditions. Alternatively, the use of a Schöninger combustion after the milk dehydration was evaluated. The residue was taken up in 0.12 mol l-1 KOH solubilization. For typical samples, recoveries varied from 94.5 to 105%, based on the amounts of both organic matter destroyed. The accuracy of the method was established by using a certified reference material (IAEA A-11, milk powder) and a manual method. The proposed flow injection method is now applied as an indicator of milk quality in a Brazilian milk production system.
The Cu(II)-catalyzed oxidation of 2,6-dichlorophenolindophenol (DCPI) in the reduced form by hydrogen peroxide was exploited for the development of a flow injection procedure for copper determination in plant digests and natural waters. For selectivity enhancement, a Chelex-100 resin mini-column (50 - 100 mesh) was incorporated to the manifold. The proposed system is very stable, handles about 60 samples per hour, yields precise results (RSD<2% within 5.0 and 70.0 μg l-1 Cu) and requires only 0.87 mg DCPI per measurement. Beer’s law is followed up to about 100 μg l-1 Cu and the detection limit is 0.09 μg l-1 Cu (in the injectate). Baseline drift was not observed during extended (5 h) operation periods. Results were in agreement with certified values of standard reference materials and recoveries within 95 and 104% were found.
An electric field application on ion exchange packing supports induced the release of sample solutes from the supports. When the electric field was applied temporary on the column, this phenomenon was observed as an increase in the pulsed concentration in the mobile phase. Namely a peak emerges on a chromatogram. The effect of the applied voltage on the ion exchange resin was examined by using a tiny mini-column. The sample solution was continuously passed through and the variations of effluent composition with and without application of electric field were analyzed. It was observed that amounts of increments of molar concentration of both benzoic acid and benzenesulfonic acid in mobile phase depended on the strength of the electric field. A theory of variation of distribution constant due to the electric field is proposed.
A new oxazolidine derivative was synthesized as a reagent for individual and simultaneous determinations of Cu(II) and Pd(II) using zero- and first-order derivative spectrophotometry. 5-Imino-3-(p-methoxyphenyl)-2-methyloxazolidin-4-thione (PMOX) formed colored complexes with these metal ions in aqueous and micellar media containing cetylpyridinium bromide. The first-derivative spectra of these complexes permitted a simultaneous determination of Cu(II) and Pd(II) in concentration intervals 0.27 - 2.35 and 0.43 - 4.26 μg ml-1 at zero-crossing wavelengths of 412 and 376 nm, respectively. The influence of the experimental conditions, the ionization constant of the reagent and the stoichiometry of the complexes are reported. The methods were free from any interference of a large number of other metal ions. A critical evaluation of the proposed methods was performed by a statistical analysis of the experimental data. The methods have been applied to determine copper in steel, aluminum-, and nickel-base alloys and to the determination of palladium in activated charcoal.
The 1H and 13C 2D NMR studies of pyrrolinones derivatives were performed using the method of proton detected 2D 1H, 13C correlation spectroscopy. HMQC and HMBC experiments were achieved in order to obtain the unambiguous assignment of the structures.