Urine samples were collected during the daytime and nighttime from spontaneously hypertensive model rats and normal rats without dosing. The ¹H NMR spectra were measured for their urine samples, and analyzed by a pattern recognition method, known as Principal Component Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA). The separation of urinary data due to the diurnal variation (daytime and nighttime) and also to the difference between the two strains of rat was achieved in the PCA score plot. Differences of the urinary profiles in the respective separation were effectively extracted as marker variables by the SIMCA method. NMR measurements coupled with pattern recognition methods provide a straightforward approach to inspect the disease metabolic status and the preliminary screening tool of marker candidates for further development.

View full abstract

The recent development, behavior and scope of edge plane pyrolytic graphite electrodes in electroanalysis are overviewed. Similarities to, and advantages, over multi-walled CNT modified electrodes are noted and the wide scope of applications, ranging through gas sensing, stripping voltammetry and biosensing, illustrated.

View full abstract

The formation conditions and characteristics of a liquid/liquid optical waveguide (LLW) were studied using a two-phase sheath flow, where the inner organic phase flow acted as the core and the outer aqueous flow acted as the clad. In immiscible solvent systems, i.e., toluene/water and diethyl ether/water systems, the LLWs were formed in the range of higher than ca. 600 of the Reynolds number (Re), where the linear velocity of the organic solvent was much higher than that of the aqueous solution. On the other hand, in a miscible solvent system, i.e., a tetrahydrofuran/water system, a stable LLW was formed in the range of a much lower Re than in immiscible systems. Moreover, the molecules at the toluene/water interface of the LLW were observed with both fluorescence and absorbance measurement systems. In particular, the change in the fluorescence spectrum of 1-anilino-8-naphthalenesulfonate (ANS) at the interface within 1 ms was observed by this method, indicating the usefulness of the LLW for a fast kinetic study of a liquid/liquid interface.

View full abstract

Potential cycling in the range from -0.2 to +1.2 V is used for the electrodeposition of hydrous iridium oxide films onto a screen-printed electrode from a saturated solution of alkaline iridium(III) solution. The iridium oxide redox couple shows a stable and obvious reversible redox, with the formal potential being pH dependent in the range 1 - 14. The properties, stability and electrochemical properties of iridium oxide films were investigated by cyclic voltammetry. A modified electrode showed excellent catalytic activity toward the oxidation of neurotransmitters (catecholamines) over a wide pH range (2 - 8). The electrocatalytic behavior is further exploited as a sensitive detection scheme for adrenaline and dopamine by hydrodynamic amperometry. Under the optimized conditions, the calibration curves are linear in the concentration range 0.1 - 70 and 0.1 - 15 µM for dopamine and adrenaline determination, respectively. The detection limit and sensitivity are 30 nM and 30 nA/µM for adrenaline and 15 nM and 80 nA/µM for dopamine. Finally, the analytical performance of the modified electrode was demonstrated for the elimination of interference by uric acid in catecholamines determination when present in a 1000-fold concentration excess.

View full abstract

A sensitive and selective method for simultaneous determination of carvedilol and dopamine was described. The emission wavelengths of carvedilol and dopamine were at 354 nm and 314 nm with the excitation at 290 nm, respectively. The determination of carvedilol and dopamine by normal fluorometry was difficult because the emission spectra of carvedilol and dopamine were overlapped seriously. The first derivative peaks of carvedilol and dopamine were at 336 nm and 302 nm, respectively. The linear regression equations of the calibration graphs of carvedilol and dopamine were C = 0.000557H - 0.00569 and C = 0.00438H - 0.0812, with the correlation coefficients were 0.9953 and 0.9988, respectively. The liner range for the determination of carvedilol was 0.002 µg ml^-1 to 0.02 µg ml^-1, and 0.05 µg ml^-1 to 0.6 µg ml^-1 for dopamine. The detection limits were 1 ng ml^-1 for carvedilol and 0.04 µg ml^-1 for dopamine, respectively. The relative standard derivative (RSD) of 4.38% and 4.35% was observed for carvedilol and dopamine, respectively. The recovery of carvedilol was from 95.00% to 106.7% in human serum and from 97.50% to 105.0% in urine sample. The recovery of dopamine was from 100.0% to 102.5% in human serum and from 97.50% to 105.0% in urine sample. This method is simple and can be used for determination of carvedilol and dopamine in human serum and urine sample with satisfactory results.

View full abstract

The spectrophotometric titration of cobalt(II) with CaCl₂ was carried out in mixed solvents of 2-propanol and water at different solvent compositions of 2-propannol, water and CaCl₂ to analyze the salting-out extraction mechanism of Co(II) by the addition of CaCl₂ from the mixed solvents. The formation constants of β_CoCl4^2- = [CoCl₄^2-][Co²⁺]^-1[Cl^-]^-4 in both the organic and aqueous phases were determined thorough non-liner regression of the spectrophotometric titration data by a computer program SPECFIT/32^TM. The values of log β_CoCl4^2- in the aqueous phases were -4.26 ± 0.03, -4.03 ± 0.07, -3.83 ± 0.04, -3.69 ± 0.03 and -3.46 ± 0.01 at mole fractions of 2-propanol of 0.026, 0.023, 0.017, 0.014 and 0.012, respectively, and at [CaCl₂]/mol dm^-3 values of 3.555 (I = 10.6), 4.276 (I = 12.8), 4.916 (I = 14.7) and 5.444 (I = 16.3), respectively. The formation constants of [CoCl₄^2-] in the organic phase were 5.70 ± 0.06, 5.44 ± 0.03, 5.36 ± 0.06, 5.10 ± 0.04 and 4.84 ± 0.05 at mole fractions of water of 0.431, 0.441, 0.444, 0.447 and 0.451, respectively, and at [CaCl₂]/mol dm^-3 of 0.941(I = 2.8), 0.943 (I = 2.8), 1.013 (I = 3.0), 1.090 (I = 3.3) and 1.165 (I = 3.5), respectively. These results suggest the formation of [CoCl₄^2-] of 23 - 90% in the aqueous phase at the above mole fractions and the quantitative formation of [CoCl₄^2-] in the organic phase. The extraction percentage of [CoCl₄^2-] increased with an increase in [CaCl₂]. The distribution constant, K_D (= [CoCl₄^2-]_org/[CoCl₄^2-]_aq), however, decreased and became constant with [CaCl₂]. The detailed extraction mechanism of Co(II) is discussed.

View full abstract

An analytical method was developed to determine pesticides of various chemical classes in soil, juice and honey using analyte protectants to counteract the enhancement of the chromatographic response produced by the presence of matrix components (matrix effect). This effect was more pronounced for soil and honey samples than for juice samples; regarding the pesticide chemical class, organochlorine pesticides were less affected by the presence of matrix components than triazines and organophosphorus pesticides. Several analyte protectants (2,3-butanediol, L-gulonic acid γ-lactone, corn oil and olive oil) were tested for counteracting the observed matrix effect. L-Gulonic acid γ-lactone was an effective protecting agent for most of the pesticides studied in soil and honey samples, whereas olive oil was very effective for juice samples. The combination of these two protectants was found to be an effective analyte protectant for all compounds in soil and honey samples.

View full abstract

Fast-flow spherical homogeneous agarose beads were prepared by an emulsification method, and were cross-linked and activated by repeated treatment with allylbromide and bromine/water, followed by alkali. Bis(2-aminopyridyl)dioxime (APD) was synthesized by the reaction of 2-aminopyridine, and dichloroglyoxime and characterized by melting-point as well as IR, ¹HNMR, ¹³CNMR and MS spectroscopies. APD was chemically linked to activated agarose beads to be employed for the column preconcentration of metal ions. Capacity measurements for eight metal ions indicated a high selectivity of the adsorbent towards Cu²⁺ with a capacity of 25.7 µmol per ml packed adsorbent. A factorial design was used for optimization of the effects of 5 different variables on the recovery of Cu²⁺. Under the optimized conditions, Cu²⁺ was quantitatively accumulated on a 0.25 ml packed column of the adsorbent in the pH range of 4 to 6, and simply eluted with 2 ml of a 1 mol l^-1 hydrochloric acid solution. The column could tolerate salt concentrations up to 0.5 mol l^-1, sample flow rates up to 15 ml min^-1, and sample volumes beyond 1000 ml. Matrix ions of Na⁺, Mg²⁺ and Ca²⁺ and potentially interfering ions of Ni²⁺, Cd²⁺, Zn²⁺, Fe³⁺ and Co²⁺ with relatively high concentrations did not show any significant effect on the analyte's signal. Preconcentration factors up to 500 and a detection limit of 0.16 µg l^-1 were obtained for the determination of the analyte by flame AAS. Application of the method to the determination of natural and spiked copper in river water and seawater samples resulted in quantitative recoveries.

View full abstract

A capillary zone electrophoresis (CZE) method has been developed for investigating the physicochemical characteristics of five Strychnos alkaloids in Strychnos nux-vomica L. Firstly, the dissociation constants of the five Strychnos alkaloids were determined, based on the relation between the effective mobility of the solutes and the buffer pH. The mathematical relationship was strictly deduced from the fundamental electrophoretic theory and the dissociation equilibrium. Secondly, an equation describing the relation between the migration time of alkaloids of similar structure and their molecular weights was developed and used to predict the migration order and to calculate the electrosomotic velocity. The results predicted by the theory agreed with those from experiments.

View full abstract

A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg²⁺, Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, “cleaning” solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO₃ vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 µg L^-1. The precision of determination was satisfactory for the respective concentration level.

View full abstract

A palladium hexacyanoferrate (PdHCF) film as an electrocatalytic material was obtained at an aluminum (Al) electrode by a simple electroless dipping method. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of hydrazine. The electrocatalytic oxidation of hydrazine was studied by cyclic voltammetry and rotating disk electrode voltammetry techniques. A calibration graph obtained for the hydrazine consisted of two segments (localized at concentration ranges 0.39 - 10 and 20 - 75 mM). The rate constant k and transfer coefficient α for the catalytic reaction and the diffusion coefficient of hydrazine in the solution D, were found to be 3.11 × 10³ M^-1 s^-1, 0.52 and 8.03 × 10^-6 cm² s^-1 respectively. The modified electrode was used to amperometric determination of hydrazine in photographic developer. The interference of ascorbic acid and thiosulfate were investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level of stability during electrochemical experiments, making it particularly suitable for analytical purposes.

View full abstract

1-(2-Hydroxy-4-methoxybenzophenone)-4-phenylthiosemicarbazone (HMBPT) was investigated as a new reagent for the flotation of vanadium(IV). At pH ∼1.5, vanadium(IV) forms a 1:1 pale-violet complex with HMBPT in aqueous solution. An intense clear violet layer was formed after flotation, by adding an oleic acid (HOL) surfactant. The composition of the float was 1:1 [V(IV)]:[HMBPT]. A highly selective and sensitive spectrophotometric procedure was proposed for the determination of microamounts of V(IV) as its floated complex. The molar absorptivities of the V(IV)-HMBPT and V(IV)-HMBPT-HOL systems were 0.4 × 10⁴ and 0.12 × 10⁵ L mol^-1 cm^-1 at 560 nm, respectively. The formation constants of the species formed in the presence and absence of HOL were 4.6 × 10⁷ and 8.7 × 10⁵ L mol^-1, respectively. Beer's law was obeyed up to 1 × 10^-4 mol L^-1 in the aqueous layer as well as in the oleic acid layer. The HMBPT-V(IV) complexes formed in the aqueous solution and scum layer were characterized by elemental analysis, infrared and UV spectrophotometric studies. The mode of chelation between V(IV) and HMBPT is proposed to be due to a reaction between the protonated bidentate HMBPT ligand and V(IV) through the S=C and N=C groups. Interferences from various foreign ions were avoided by adding excess HMBPT and/or Na₂S₂O₃ as a masking agent. The proposed flotation¹ method was successfully applied to the analysis of V(IV) in synthetic mixtures, wastes of power stations, simulated samples and in real ores. The separation mechanism is discussed.

View full abstract

The present paper describes the on-line coupling of a flow-injection system to a new technique, thermospray flame furnace-AAS (TS-FF-AAS), for the preconcentration and determination of copper in water samples. Copper was preconcentrated onto polyurethane foam (PUF) complexed with ammonium O,O-diethyldithiophosphate (DDTP), while elution was performed using 80% (v/v) ethanol. An experimental design for optimizing the copper preconcentration system was established using a full factorial (2⁴) design without replicates for screening and a Doehlert design for optimization, studying four variables: sample pH, ammonium O,O-diethyldithiophosphate (DDTP) concentration, presence of a coil and the sampling flow rate. The results obtained from the full factorial and based on a Pareto chart indicate that only the pH and the DDTP concentration, as well as their interaction, exert influence on the system within a 95% confidence level. The proposed method provided a preconcentration factor of 65 fold, thus notably improving the detectability of TS-FF-AAS. The detection limit was 0.22 µg/dm³ and the precision, expressed as the relative standard deviation (RSD) for eight independent determinations, was 2.7 and 1.1 for copper solutions containing 5 and 30 µg/dm³, respectively. The procedure was successfully applied for copper determination in water samples.

View full abstract

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography/mass spectrometry (GC/MS) method was developed to determine 3-chloropropane-1,2-diol (3-MCPD) in hydrolyzed vegetable protein and Chinese soy sauce. The 3-MCPD was firstly derivativized with phenylboronic acid in aqueous solution at 90°C for 10 min, then extracted by HS-SPME and finally detected with GC/MS, parameters related to both the derivative reaction and the HS-SPME process were optimized. The proposed method has a linear range of 0.0194 - 394 µg g^-1, a detection limit of 3.87 ng g^-1 (S/N = 3), and a precision of RSD = 7.5% (n = 5). Seventeen real samples, including four HVPs and thirteen soy sauce samples, were analyzed to examine the feasibility of the proposed procedure; with a concentration of 3-MCPD and acceptable recoveries at 0.71 µg g^-1 spiked levels were obtained. Being simpler, faster and more environmentally benign than the existing methods, this method is accurate and suitable for routine analysis.

View full abstract

Equations are presented by which potential-volume data from redox titrations can be analyzed. Mixtures of analytes as well as of titrants may be analyzed, yielding for each component its concentration, number of electrons, and reduction potential. A novel weighting function ensures endpoint accuracy in fitting. Standard deviation of each parameter is obtained. The equations can be readily implemented in Microsoft Excel. Agreement with true values and good precision of fit parameters is demonstrated for a number of test cases. Use of these exact equations enables analysis of analyte mixtures without prior separation using single titrant or titrant mixtures. The equations were used to demonstrate that N-bromosuccinimide, a useful oxidant for organic analytes, undergoes hydrolysis.

View full abstract

The interaction of aqua (N-salicylideneglycinato)copper(II) (Cu(salgly)²⁺) complex with calf thymus DNA has been investigated by cyclic voltammetry. Potential-modulated DNA cleavage in the presence of Cu(salgly)²⁺ complex was performed at a gold electrode in a thin layer cell. DNA can be efficiently cleaved by electrochemically reducing Cu(salgly)²⁺ complex to Cu(salgly)⁺ complex at -0.7 V (vs. Ag/AgCl). When the solution was aerated with a small flow of O₂ during electrolysis, the extent of DNA cleavage was dramatically enhanced, and hydroxyl radical scavengers inhibited DNA cleavage. These results suggested that O₂ and hydroxyl radical were involved in potential-modulated DNA cleavage reaction. The percentage of DNA cleavage was enhanced as the working potential was shifted to more negative values and the electrolysis time was increased. It was also dependent on the ratio of Cu(salgly)²⁺ complex to DNA concentration. The cleaved DNA fragments were separated by high performance liquid chromatography (HPLC). The experimental results indicated that the method for potential-modulated DNA cleavage by Cu(salgly)²⁺ complex was simple and efficient.

View full abstract

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO₃; v = 2.0 mV s^-1 vs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L^-1 was obtained. The detection limit was estimated to be 5 µg L^-1. The precision for six determinations of 0.05 and 0.26 mg L^-1 Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.

View full abstract

Certain wear metals (Fe, Cr, Ni, Cu and Zn) of various lubrication oils were determined by means of ICP-OES and FAAS. The kerosene dilution method, which is used widely together with ICP-OES, was applied with both methods here. Calibration standards were made from a commercial organo-metallic standard. Our aim was to clarify the possibility of using the quick kerosene dilution method together with FAAS for a rapid check for certain indicator metals. Metal determinations with FAAS were accurate enough for quantitative work in machine condition diagnostics and waste oil characterization, when compared with those with ICP-OES.

View full abstract

A capillary electrophoresis with chemiluminescence method has been developed for the determination of rutin and chlorogenic acid based on its enhancing effect on the luminol-ferricyanide system. Under the optimum conditions, the analytes could be separated within 5 min, and the detection limits of the proposed method were 0.22 µg/ml for rutin and 0.50 µg/ml for chlorogenic acid, respectively. The method was successfully applied to the analysis of rutin and chlorogenic acid in real samples.

View full abstract

Layered thin films composed of concanavalin A (Con A) and sugar-bearing polymers were prepared by a layer-by-layer deposition of Con A and the polymer on a solid surface. The sugar-induced disintegration was studied. Con A-polymer layered films could be successfully prepared using a maltose-bearing polymer (PV-MA), while melibiose- and glucose-bearing polymers (PV-MEA and PV-G) did not afford a layered film, due to a weak affinity of PV-MEA and PV-G to Con A. The Con A/PV-MA layered film was stable in pH 7 and 8 solutions, while in a pH 6 medium the film was slightly unstable. The Con A/PV-MA film was disintegrated upon the addition of sugars in solution owing to a preferential binding of the sugars to the binding site of Con A in the film. The disintegration rate was dependent on the type of sugar and its concentration. The Con A/PV-MA film was disintegrated rapidly upon the addition of methyl α-D-mannopyranoside, while the rate was slower upon the addition of the same concentration of D-mannose, D-glucose and methyl α-D-glucopyranoside. The present system may be useful for constructing sensitive devices that can release a drug or other functional molecules in response to sugars.

View full abstract