We succeeded in the detection of the sitting-atop (SAT) copper(II) complex of TPP (5,10,15,20-tetraphenylporphyrin) in acetonitrile (AN) as a solvent with a very low Brønsted basicity, where two pyrrolenine nitrogens in the Cu(II)-SAT complex coordinate to the metal ion and two protons still remain on the pyrrole nitrogens. The structure parameters around the copper(II) ion in the Cu(II)-SAT complex, as determined by a fluorescent EXAFS method, suggest an axially elongated and equatorially distorted six-coordinate geometry. We measured the rates of the formation reaction of the SAT complexes for a series of transition metal(II) ions in AN using the stopped-flow technique. We propose the mechanism where there is a rapid deformation equilibrium of the porphyrin ring prior to the rate-determining step of the bond rupture of a coordinated solvent molecule on the metal(II) ion. Furthermore, we measured the rates of the deprotonation reaction of the Cu(II)-SAT complex by some Brønsted bases and indicated that the rate-determining step is the attack of the base on the proton of the pyrrole nitrogen in the SAT complex. Finally, a unified mechanism relevant to the porphyrin metalation mechanism has been proposed.
A selective and sensitive chemiluminometric flow sensor for the determination of L-glutamate in serum, based on immobilized oxidases such as glutamate oxidase (GOD), uricase (UC) and peroxidase (POD), is described herein. The principle for the selective chemiluminometric detection for L-glutamate is based on coupled reactions of four sequentially aligned immobilized oxidases, UC/POD/GOD/POD in a flow cell. The immobilized UC was employed to decompose urate, which is one of the major interfering components in serum for a lumino1-H2O2 chemiluminescence reaction. The H2O2 produced from the UC reaction readily reacted with reducing components, such as ascorbate and glutathione, and then the excess H2O2 was decomposed by the immobilized POD. L-Glutamate in the sample plug was enzymatically converted to H2O2 with immobilized GOD. Subsequently, the peroxide reacts with luminol on the immobilized POD to produce chemiluminescenece, proportional to glutamate concentration. The enzymes were immobilized on tresylated poly(vinyl alcohol beads). The immobilized enzymes were packed into a TPFE tube (1.0 mm i.d. × 60 cm), in turn, and used as a flow cell. The sampling rate was 30 h-1 . The calibration graph for L-glutamate is linear for 20 nM - 5 µM; the detection limit (signal-to-noise = 3) is 10 nM.
A PVC-based membrane electrode for lead ions based on hexathia-18-crown-6-tetraone as membrane carrier was prepared. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a lead concentration range from 1.0 × 10-6 to 8.0 × 10-3 M at 25°C, and was found to be very selective, precise and usable within the pH range 3.0 - 6.0. The electrode was successfully used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.
β-Alanine was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation process of the amino-containing compound. X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV) proved the immobilization of β-alanine monolayer on GCE. The electrode shows strong electrocatalytic functions to dopamine (DA) and ascorbic acid (AA), reducing the overpotentials by 0.20 V and 0.23 V, respectively. Due to its different catalytic effects toward DA and AA, the modified electrode resolved the overlapping voltammetric responses of DA and AA into two well-defined voltammetric peaks by CV or differential pulse voltammetry (DPV), which can be used for the simultaneous determination of these species in a mixture. The catalytic peak current obtained from DPV was linearly related to DA and AA concentrations in the ranges of 4.0 × 10-6 - 5.0 × 10-4 mol/L and 2.0 × 10-5 - 6.0 × 10-3 mol/L with correlation coefficients of 0.997 and 0.995, respectively. The detection limits (3σ) for DA and AA were 2.4 × 10-6 mol/L and 1.2 × 10-5 mol/L, respectively. The electrode shows good sensitivity, selectivity and stability, and has been applied to the determination of DA and AA simultaneously in samples with satisfactory results.
In order to lower the redox potentials of Os(III/II) complexes, the mixed ligand complexes of Os(II) were synthesized. The redox potentials of Os(III/II) complexes could be lowered by the use of 4,4′-dimethyl-2,2′-bipyridine (dmbpy), imidazole (Him) or its derivatives, and chloride ion as ligands, e.g., values of the redox (formal) potentials of 628 mV vs. Ag/AgCl for [Os(bpy)3]3+/2+ (bpy: 2,2′-bipyridine) and -6 mV for [OsCl(Him)(dmbpy)2]2+/+ were given in deaerated 0.1 mol dm-3 phosphate buffer (pH 7.0). The evaluation of Os(II) complexes as electron transfer mediators accessible for amperometric glucose sensors was examined according to the determination of the redox potentials of Os(III/II) complexes and the second-order rate constants for electron transfer between glucose oxidase (GOx) in reduced form and the Os(III) complex. Although the Os(II) complexes with lower redox potentials tended to decrease the second-order rate constants ks, the ks values for the majority of Os(II) complexes synthesized in this study were greater than that for ferrocenecarboxylic acid. Acceleration of the electron-transfer reaction is attributable to the hydrogen bonding and/or the electrostatic interaction between the Os(II) complexes and GOx. It may be consequently concluded that the mixed ligand complexes of Os(II) with bpy (dmbpy), Him (its derivatives), and Cl- can act as more efficient electron transfer mediators for the fabrication of amperometric glucose sensors.
The chemiluminescent (CL) detection of epinephrine (EP) with lucigenin (Luc) was performed using a micro flow cell fabricated on a silicon chip. A solution of EP was injected into the Luc carrier stream. The Luc solution containing EP and an alkaline solution were successively poured into the flow cell by a pressure-driven flow system. Two types of flow cells were fabricated for estimating the effect of the mixing modes in the flow cells on the intensity of light emission. In flow cell 1, two streams entered through separate inlet ports and merged to flow adjacently. In flow cell 2, a Luc solution containing EP was split up to 36 partial flows by passage through the nozzles, and was injected into the alkaline solution. The intensity of light emission in flow cell 2 increased markedly compared to that in flow cell 1. The detection limit of 8.0 × 10-7 M for EP in flow cell 2 was a factor of six-times better than that in flow cell 1. The improvement in the sensitivity for EP could be explained in terms of the distortion of laminar flow in flow cell 2.
Synergistic enhancement of the extraction of lanthanoid(III) (Ln) with 2-thenoyltrifluoroacetone (Htta) in benzene has been found by the addition of tris(4-isopropyltropolonato)cobalt(III) (Co(ipt)3). The synergistic effect of Co(ipt)3 was ascribed to the formation of a 1:1 adduct of Ln(tta)3 with Co(ipt)3, i.e., a binuclear complex, in the organic phase. The adduct formation constant (βs,1) determined by the extraction equilibrium analysis was reasonably consistent with that determined by spectrophotometry. The βs,1 values decreased with increase in the atomic number of Ln and showed a large difference between light and heavy Ln. Spectroscopic studies were performed to explain the difference in the βs,1 values. Electronic absorption spectra showed that the change in the structure of Co(ipt)3 complexed with the light Ln chelate is larger than that with the heavy Ln. The IR spectra showed the displacement of the coordinated water molecules of the light Ln chelates with Co(ipt)3. On the other hand, the adduct formation of heavy Ln was caused by the hydrogen bonding between Co(ipt)3 and the coordinated water of the Ln chelate.
A new simple, accurate and precise spectrophotometric method for the determination of six phenothiazine drugs in pure form and in dosage forms is described. The method is based on the oxidation of the studied drugs by a known excess of Chloramine-T in hydrochloric acid medium and subsequent determination of the unreacted oxidant by reacting it with indigocarmine in the same acid medium. The reacted oxidant corresponds to the drug content. The colored species exhibits maximum absorption at 610 nm. The apparent molar absorptivity values and Sandell sensitivity values are in the range 1.53 × 104 - 2.96 × 104 l mol-1 cm-1 and 13.75 - 37.15 ng cm-2, respectively. The method is highly sensitive and suitable for 1 - 15 µg ml-1 concentrations with the detection limits being in the range, 0.0651 - 0.1724 µg ml-1 . The method was successfully applied to the studied drugs in their dosage forms. The results are reproducible within ±1% and compare favorably with those obtained by the procedures of the British Pharmacopeia.
Manganese is quantitatively retained on 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP)-ammonium tetraphenylborate with microcrystalline naphthalene or by a column method in the pH range 7.5 - 10.5 from large volumes of aqueous solutions of various samples. After filtration, each solid mass consisting of the manganese complex and naphthalene was dissolved with 5 ml of dimethylformamide and the metal was determined by flame atomic absorption spectrometry. Manganese complex can alternatively be quantitatively adsorbed on ammonium tetrphenylborate-naphthalene adsorbent packed in a column and determined similarly. About 0.1 µg of manganese can be concentrated in a column from 500 ml of aqueous sample, where its concentration is as low as 0.2 ppb. Eight replicate determinations of 1.0 ppm of manganese gave a mean absorbance of 0.224 with a relative standard deviation of 1.8%. The sensitivity for 1% absorption was 19 ppb. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the trace determination of manganese in various standard samples.
A chemiluminescence method with potassium permanganate was developed for use as an indicator of organic pollutants in fresh water. This method could be applied to the determination of organic pollutants in seawater as well. However, the flow chemiluminescence method suffered from the interference of chloride ions at the same concentration of seawater because of the production of manganese dioxide in the oxidation of chloride ions with permanganate. The conditions (concentrations of potassium permanganate and sulfuric acid and sample volume, i.e. flow injection method) were chosen to minimize the interference of chloride ions. The chemiluminescence method shows a good correlation with the chemical oxygen demand method on fresh water added artificial sea salt and seawater samples. Natural seawater was analyzed by the chemiluminescence method. The results obtained were compared with those obtained by chemical oxygen demand under the alkaline condition and total organic carbon methods. The chemiluminescence method has higher sensitivity and reproducibility than the conventional chemical oxygen demand and total organic carbon methods.
Two simple, rapid and sensitive spectrophotometric methods have been proposed for the determination of vanadium(V) using butaperazine dimaleate (BPD) and propionyl promazine phosphate (PPP). These methods are based on the formation of red-colored radical cations on reaction with vanadium(V) in phosphoric acid medium, with their absorbance maxima at 513 nm. Beer’s law is valid over the concentration range of 0.25 - 5.0 µg ml-1 and 0.2 - 4.0 µg ml-1 , with Sandell’s sensitivity values of 6.1 ng cm-2 and 6.0 ng cm-2 for BPD and PPP respectively. The proposed methods have been successfully applied to the analysis of vanadium steels, minerals, biological samples and soil samples.
A new convenient dissolution method for Fe-Rh alloys has been developed. Aqua regia has been used for the dissolution of rhodium alloy samples. However, it is difficult to dissolve high-concentration rhodium (more than 50 mass%) in aqua regia, because a rhodium-passivity on the alloys surface occurs with nitric acid. By using hydrochloric acid containing a small volume of nitric acid, Fe-Rh (24 - 64 mass%) alloys could be completely decomposed and dissolved under mild experimental conditions. The principal advantages of this method are simplicity and time-saving compared with other dissolution methods.