A monolayer membrane of 2-mercaptobenzothiazole (MBT) was prepared on a gold electrode through a self-assemblyprocedure. The monolayer structure and the electrochemical properties were investigated by various electrochemicaltechniques, like cyclic voltammetry and an impedance measurement with external redox. Experiments show that MBTcan form a closely packed monolayer that can be charged due to the active N atom. The amount of charge on themembrane surface varies with the solution pH, and the monolayer shows “opening and closing” which depends on thesolution pH. The electrostatic interaction of the monolayer with other ions is also related to the pH in solution. Animpedance analysis shows that the heterogeneous electron-transfer rate of a fast redox like Fe(CN)63-/4- decreases from 1.2 × 10-2 to 4.7 × 10-5 cm s-1 in neutral solution due to blockage of the self-assembled monolayer membrane.
The adsorptive behavior of hemoglobin at a platinum electrode is investigated by employing cyclic voltammetry. On the basis of the investigations, an electrochemical method for the determination of hemoglobin is developed. This method is shown to be simple and sensitive. The detection limit can be as low as 1.6 nmol/L. Since the working electrode does not need to be modified and the experimental procedure is very simple, this method might be useful for protein determination in the future.
The interaction of a cobalt compound, tris(2,2′-bipyridyl)cobalt(III) perchlorate (Co(bpy)3(ClO4)3·3H2O), with DNA immobilized on a biosensor has been investigated by using a piezoelectric impedance technique. The changes of equivalent circuit parameters were used to characterize the changes of the interfacial properties of the piezoelectric biosensor in the reaction system. It was found that the interaction of cobalt compound with double-strained DNA (dsDNA) could be described by a sum of two exponential functions, suggesting two corresponding kinetic steps. As for dsDNA, the change of static capacitance showed a linear correlation with time. Comparative experiments indicated that dsDNA with double-helical structure is more easily bound with cobalt compound than single-strained DNA (ssDNA). From the frequency curve, some parameters related to this interaction, such as cross-linking ratio, binding ratio, and the maximum initial rate were roughly estimated to be 2%, 1.15, 0.72 Hz/s (or 0.12 Hz/s for ssDNA), respectively. The linear relationship between the frequency change and the motional resistance was verified to reflect the changes of the density-viscosity in the biological reaction.
An absorbance-based optic fiber probe for determination of ferrous ions is described. It is based on 4,7-diphenyl-1,10-phenanthroline as a sensitive reagent which was immobilized on polymethylmethacrylate (PMMA) using a new immobilization method. The proposed probe responded linearly to the Fe2+ concentration in the range of 0.03 - 1.0 mg l-1. The response time required to reach a stable signal was short (less than 10 min). The probe exhibited pH and temperature independence, small ion interference, good selectivity, reproducibility and stability. It was applied for direct analysis of Fe2+ ions in natural water. The results were comparable to those obtained by a conventional spectrophotometric method. The results of recovery tests were also satisfactory.
Studies on C-3 epimerization of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] were performed. 3-Epi-24,25(OH)2D3 was found to circulate in the blood of rats administered 24,25(OH)2D3, which was confirmed in comparison with a standard sample based on its chromatographic behavior during inclusion high-performance liquid chromatography using γ-cyclodextrinas a mobile phase additive and data obtained from liquid chromatography (LC)/mass spectrometry (MS) and gas chromatography/MS. The C-3 epimerization mechanism was investigated in in vitro experiments using [3α-2H]-24,25(OH)2D3. The disappearance of deuterium was monitored by LC/MS. As a result, it was clarified that the 3-epimer was formed via the 3-oxo-form as an intermediate. This epimerization was also found to be controlled by the enzyme existing in the liver cytosol fraction and to require NAD and NADPH as coenzymes.
The electric field above specimen surfaces mounted in specimen holders was investigated. After confirming an agreement of the field distortion area obtained from SIMS experiments using a Cameca IMS-4f ion microscope and computer simulation, the field distortions above specimen surfaces of various types of holder were estimated. Two findings were obtained: (i) the field distortion area near to the window edge of the holder increases along with an increase in the faceplate thickness of the holder, and (ii) a holder with a tapered faceplate produces a more uniform electric field than does that with a right-angled window edge.
A spectrophotometric flow titration procedure for ascorbic acid in fruit juices and soft drinks based on volumetric fraction variation employing a reaction with 2,6-dichloroindophenol is described. A flow network was designed to implement the multicommutation process and a set of microcomputer controlled three-way solenoid valves was employed to handle the insertion of the titrand and titrant solutions into the analytical path. All the steps involved in the titration procedure were carried out automatically without any operator assistance. Fruit juices and soft drinks could be analyzed without any prior chemical treatment. Accuracy was assessed by comparing results with those obtained by the reference method (AOAC). No significant differences at 95% confidence level were observed. Other profitable features were achieved such as a percentual standard deviation of results of 1.1% (n = 5) for a typical juice sample containing 1.2 mmol L-1 ascorbic acid, a low sample consumption (6 µL per run), and an analytical throughput ranging from 5 to 30 determinations per hour for sample concentrations ranging from 0.6 to 6.0 mmol L-1.
The use of chemically modified chloromethylated polystyrene-PAN, CMPS-PAN ion-exchanger for the separation of Au(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Pd(II) and Zn(II) from aqueous solution is described. After preconcentration, the heavy cations under investigation were determined using atomic absorption spectrometry (AAS). The distribution coefficient, Kd and the percentage concentration of the studied metal ions on the ion-exchanger at equilibrium, CM,eqm, % are evaluated as a function of pH, mass of ion-exchanger and shaking time. The calculated Kd values for the investigated cations are in the range of 25 - 7.9 × 105 cm3 g-1. The interfering effects of different foreign ions were studied. The chelates formed between CMPS-PAN ion-exchanger and the investigated metal ions were characterized by FT-IR spectrometry, potentiometry and thermal analysis. The present method is simple and rapidly applicable for the microdetermination of eleven heavy metal ions at ppb levels. Analytical applications for the preconcentration and separation using the modified CMPS-PAN ion-exchanger and the determination of the studied metal ions in tap, Nile, waste and sea water samples, human urine, milk (synthetic and natural) and some ores were carried out.
Cobalt was quantitatively retained by disodium 1-nitroso-2-naphthol-3,6-disulfonate (nitroso-R salt) and tetradecyldimethylbenzylammonium chloride (TDBA+Cl-) on microcrystalline naphthalene in the pH range 3.6 - 8.2 from large volumes of aqueous solutions of various alloys and biological samples. After filtration, a solid mass consisting of the cobalt complex and naphthalene was dissolved with 5 ml of dimethylformamide (DMF), and the metal was determined by third-derivative spectrophotometry. The cobalt complex could alternatively be quantitatively adsorbed on tetradecyldimethylbenzylammonium-naphthalene adsorbent packed in a column and determined similarly. The detection limit was 30 ppb (signal to noise ratio = 2) and the calibration curve was linear for 0.1 - 11 ppm in dimethylformamide solution with a correlation coefficient of 0.9996 by measuring the distance, d3A/d λ3, between λ1 (612 nm) and λ2 (579 nm). Eight replicated determinations of 2 ppm of cobalt in dimethylformamide solution gave a mean intensity (peak to peak signal between λ1 and λ2) of 0.436 with a relative standard deviation of ±0.91%. The sensitivity of the method was 0.215 (d3A/dnm3) ml/µg, which was found from the slope of the calibration curve. Various parameters, such as the effect of the pH, the volume of the aqueous phase and the interference of a number of metal ions on the determination of cobalt has been studied in detail to optimize the conditions for the determination cobalt in various alloys and biological samples.
Scandium has been preconcentrated from a large volume of its aqueous solution after solid phase extraction of its 1-(2-thiazolylazo)-2-naphthol chelate onto ammonium tetraphenylborate-naphthalene adsorbent in the pH range 4.0 - 5.8. The solid mass consisting of metal complex along with the adsorbent was dissolved in 5 ml of DMF and quantified by second derivative spectrophotometry. The calibration graph is linear in the concentration range 0.08 - 2.8 µg ml-1 with a correlation coefficient of 0.9998. The sensitivity of the method as found from the slope of the calibration plot is 0.185 (d2A/dλ2 ) ml µg-1. Nine replicate determinations of 7.0 µg of scandium in 5 ml of final DMF solution give second derivative amplitudes as 0.255 with a relative standard deviation of 0.92%. The various instrumental and experimental variables are optimized. The conditions developed have been utilized for its determination in various standard and synthetic samples. The proposed method is found to be reproducible, reliable, sensitive, selective and economical.
A flow injection method has been developed for the determination of lead in steel samples by coupling on-line preconcentration on a lead selective resin, Pb·Spec™, with flame atomic absorption spectrometry. The sample prepared as a nitric acid solution is passed through a column packed with Pb·Spec™. The lead retained on the column is then eluted with ammonium oxalate solution and introduced directly into the nebulizer of a flame atomic absorption spectrophotometer. The proposed method was successfully applied to the determination of lead in pure iron certified reference material [0.19 ± 0.01 ppm (n=6); certified value: 0.2 ppm] and lead-free cutting steel certified reference material [0.0952 ± 0.0008% (n=3); certified value: 0.097%]. The detection limit (3σ) was 0.05µg of lead.
A combination technique of some kinds of enzymatic reactions for flow injection analysis with an immobilized enzyme-reactorcolumn was studied. This system consisted of hand-made reactor columns packed with glucose oxidase and horseradish peroxidase immobilized onto chitosan beads, and a fluorometric detector. It was applied for the determination of glucose in some beverages, Japanese Sake and liquor samples. Under the recommended conditions, it could determinea sample within 10 min. The calibration curve for glucose was linear from 20.0 mg dm-3 to 0.5 mg dm-3 in the low-sensitivityregion of the detector, and from 0.5 mg dm-3 to 30 g dm-3 in the high-sensitivity region of the detector. The detection limit (S/N=10) was 30 µg dm-3 as the concentration of glucose, and 54 ng as its absolute amount. There was no interference from major substances present in either beverage or serum samples.