Copper–mercury film electrode for cathodic stripping voltammetric determination of Se(IV)

The copper-mercury film electrode has been suggested for the determination of Se(IV) in a wide range of concentration from 1x10(-9) to 1x10(-6) mol L(-1)by square-wave cathodic stripping voltammetry. Insufficient reproducibility and sensitivity of the mercury film electrode have been overcome by using copper(II) ions during the plating procedure. Copper(II) has been found to be reduced and form a reproducible copper-mercury film on a glassy carbon electrode surface. The plating potential and time, the concentration of copper(II) and the concentration of the supporting electrolyte have been optimised. Microscopy has been used for a study of the morphology of the copper-mercury film. It has been found that it is the same as for the mercury one. The preconcentration step consists in electrodeposition of copper selenide on the copper-mercury film. The relative standard deviation is 4.3% for 1x10(-6) mol L(-1) of Se(IV). The limit of detection is 8x10(-10) mol L(-1) for 5 min of accumulation.     

Adsorptive stripping voltammetric determination of traces of molybdenum in natural water in the presence ofα-benzoinoxime

The electrochemical behavior of the molybdenum complex of -benzoinoxime was investigated using cyclic voltammetry and linear scan voltammetry, after adsorptive accumulation of the complex onto a hanging mercury drop electrode (HMDE). The signal corresponds to the reduction of molybdenum in the complex adsorbed at the HMDE surface. Under optimal conditions, the adsorptive stripping voltammetric procedure gave an extremely low detection limit of 0.1 nM (9.6ng/l) Mo(VI) following stirred accumulation for 5 min at 0.0 V (vs. Ag/AgCl). The reduction cur rent-[Mo(VI)] relationships were linear up to 25 and 100 nM. Repetitive determinations of 10 nM solutions gave relative standard deviations of 2.2 and 3.5%, for 1 and 5-min accumulation periods, respectively. Most of the ions investigated did not interfere with the determination of molybdenum, except for tungsten. Excellent selectivity against copper was observed. The proposed procedure was applied to the direct determination of molybdenum in natural water.     

A peroxidase-based method for the determination of dopamine, adrenaline, and α-methyldopa in the presence of thyroid hormones in pharmaceutical forms

The analytical properties of two commercial plant peroxidases isolated from horseradish roots and soybean hulls in the catalysis of the transformation of some catecholamines were demonstrated in the absence and presence of thyroid hormones (l-thyroxine and 3,3′,5′-iodothyronine). For the first time the reactions of dopamine, adrenaline, and α-methyldopa oxidation with H₂O₂ catalysed by horseradish peroxidase with the addition of l-thyroxine as the amplification agent were studied and proposed as the indicator reactions for the simple and rapid enzymatic determination of the indicated catecholamines in their concentration ranges 0.5-300, 4-300, and 100-400 μM, respectively. The catalytic activity of the enzyme (characterized by the reaction rate) was controlled spectrophotometrically. The optimum conditions for the indicator reactions were thoroughly characterized. The mechanism of the stimulatory effect of l-thyroxine on the oxidation of the catecholamines was discussed. The developed enzymatic procedures were successfully applied for the determination of dopamine, adrenaline, and α-methyldopa in some pharmaceutical forms.     

Spectrofluorimetric determination of trace amounts of coenzyme A using a terbium ion–ciprofloxacin complex probe in the presence of periodic acid

A new spectrofluorimetric method was developed for the determination of trace amounts of coenzyme A (CoA). In the presence of periodic acid (H₅IO₆), CoA can remarkably enhance the fluorescence intensity of the Tb³⁺–ciprofloxacin (CIP) complex at 545 nm in a buffer solution at pH 5.4; the enhanced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of CoA. The optimal conditions for the determination of CoA were also investigated. The linear range and the detection limit for the determination of CoA were 6.08 × 10⁻⁶–1.64 × 10⁻⁵ and 2.1 × 10⁻⁸ mol L⁻¹, respectively. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess CoA in injection and biological samples. Moreover, the enhancement mechanism of the fluorescence intensity of the CoA–Tb³⁺–CIP system in the presence of H₅IO₆ is also discussed.     

Fabrication of poly(orthanilic acid)–multiwalled carbon nanotubes composite film-modified glassy carbon electrode and its use for the simultaneous determination of uric acid and dopamine in the presence of ascorbic acid

A multiwalled carbon nanotubes (MWNT) modified glassy carbon electrode (GCE) coated with poly(orthanilic acid) (PABS) film (PABS–MWNT/GCE) has been fabricated and used for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA) by differential pulse voltammetry (DPV). Scanning electron microscopy, Fourier transform infrared spectra, and electrochemical techniques have been used to characterize the surface morphology of the PABS–MWNT composite film and the polymerization of ABS on electrode surface. In comparison with the bare GCE and the MWNT-modified GCE, the PABS–MWNT composite film-modified GCE, which combines the advantages of MWNT and the self-doped PABS, exhibits good selectivity and sensitivity for the simultaneous and selective determination of UA and DA in the presence of AA. Due to the different electrochemical responses of AA, DA, and UA, PABS–MWNT/GCE can resolve the overlapped oxidation peak of DA and UA into two well-defined voltammetric peaks with enhanced current responses using both cyclic voltammetry (CV) and DPV. The peak potential separations between DA and UA are 170 mV using CV and 160 mV using DPV, respectively, which are large enough for the selective and simultaneous determination of these species. In the presence of 0.5 mM AA, the DPV peak currents are linearly dependent on the concentration of UA and DA in the range of 6–55 and 9–48 μM with correlation coefficients of 0.997 and 0.993, respectively. The detection limits (S/N = 3) for detecting UA and DA are 0.44 and 0.21 μM, respectively. The PABS–MWNT/GCE shows good reproducibility and stability and has been used for the simultaneous determination of DA and UA in the presence of AA in samples with satisfactory results.     

A novel method for the formylation of Grignard reagent

A facile and efficient method for the formylation of Grignard reagent was reported, and a new approach for the preparation of aldehydes from Grignard reagent and benzimida-zolium salts was provided.     

Application of a novel 1,1′-dimethylferricinimum dye for the determination of uric acid in urine

Water-soluble 2-hydroxypropyl-β-cyclodextrin (Hp-β-CyD), a cyclic and nonreducing oligosaccharide was used to enclose a hydrophobic guest molecule 1,1′-dimethylferrocene (DMF) to form a water-soluble yellow complex. At high concentrations (300 mM), Hp-β-CyD enclosed up to 100 mM DMF. The yellow complex was electrochemically oxidized (platinum vs Ag/AgCl poised at +450 mV) to form a blue dye, 1,1′-dimethylferricinium (DMF⁺). This is a one-electron transfer process and the ferricinium cation formed exhibited an absorption peak at 650 nm. The concentrated DMF⁺ was stable for at least 4 mo at 4°C and insensitive to a wide pH variation (pH 2–11). Application of the novel DMF⁺ complex as a colorimetric dye for the determination of uric acid in urine was successfully demonstrated. The reaction between the dye and uric acid is almost instantaneous and decrease in absorbance caused by the reduction of 1,1′-dimethylferricinium to 1,1′-dimethylferrocene can be followed at 650 nm. The results obtained agreed well with those of the reference reversed-phase HPLC method.     

A direct chemiluminescence method for the determination of nucleic acids using Ru(phen)32+–Ce(IV) system

A direct chemiluminescence method for the determination of nucleic acids has been developed based on the enhancement of nucleic acids on the chemiluminescence light emission of the reaction between Ru(phen)₃ ²⁺(phen = 1,10-phenanthroline) and Ce(IV). Under the optimum conditions, the calibration graphs are linear in the range of 5.0 × 10^–8–5.0 × 10^–5 g/mL for calf thymus DNA, 8.0 × 10^–8–5.0 × 10^–5 g/mL for fish sperm DNA and 1.0 × 10^–7–3.0 × 10^–5 g/mL for yeast RNA, respectively. The limits of detection are 1.0 × 10^–8 g/mL for calf thymus DNA, 3.1 × 10^–8 g/mL for fish sperm DNA and 5.2 × 10^–8 g/mL for yeast RNA, respectively. The final procedure allows the successful determination of calf thymus DNA, fish sperm DNA and yeast RNA in six synthetic samples. This method is simple, rapid and specific. Received: 22 January 1999 / Revised: 29 April 1999 / Accepted: 3 May 1999     

Spectrofluorimetric study and determination of desipramine in the presence of β-cyclodextrin

The native fluorescence intensity of desipramine was enhanced in the presence of β-cyclodextrin in aqueous solution. The inclusion complex formation between these compounds was studied by spectrofluorimetry. A stable complex with a 2: 1 stoichiometry of β-cyclodextrin to desipramine was formed (logβ₂ = 9.29 ± 0.01). In the presence of an optimum concentration of β-cyclodextrin, the fluorescence intensity was linearly proportional to desipramine concentration in the range of 0.1–100 μg/mL (7.2 × 10^?7?1.0 × 10^?4 M) with a limit of detection of 7 × 10^?8 M. The method was successfully applied to the detection of desipramine in its tablets.     

Electrodeposition and stripping voltammetry of arsenic(III) and arsenic(V) on a carbon black–polyethylene composite electrode in the presence of iron ions

In this work, a new sensor is proposed for the stripping voltammetric determination (anodic stripping voltammetry—ASV) of total arsenic(V) or arsenic(III). The sensor is based on an Fe-modified carbon composite electrode containing 30 % carbon black–high-pressure polyethylene (CB/PE). The modification with iron is achieved by the addition of Fe(III) or Fe(II) ions to the sample solution and co-electrodeposition of iron and arsenic on the CB/PE electrode. In anodic stripping voltammetry, two peaks are observed: an Fe peak at ?0.45 or ?0.29 V and a peak at 0.12?±?0.07 V which depends on the arsenic concentration and corresponds to the As(0) → As(III) oxidation, as is the case with other solid electrodes. The optimum conditions proposed for ASV determination of As(V) and As(III) in solutions in the presence of dissolved oxygen are the following: the background electrolyte is 0.005 M HCl containing 0.5–1 mg/?L Fe(III) for As(V) and containing 1.0–1.5 mg/?L Fe(III) for As(III), respectively; E _dep?=??2.3 V; rest period at ?0.10 V for 3–5 s before the potential sweep from ?0.2 to +0.4 V; scan rate is 120 mV/?s. The detection limit (LOD, t?=?120 s) for As(III) and As(V) is 0.16 and 0.8 μg/?L, respectively. Various hypotheses on the effect of Fe ions and atoms on the electrodeposition and dissolution of arsenic are considered. The new method of determination of As(III) and As(V) differs from known analogues by its simplicity, low cost, and easy accessibility of the electrode material. It allows the voltammetric determination of total arsenic after chemical reduction of all its forms to As(III) or after their oxidation to As(V).     

A novel method of liquid chromatography–tandem mass spectrometry combined with chemical derivatization for the determination of ribonucleosides in urine

Ribonucleosides are the end products of RNA metabolism. These metabolites, especially the modified ribonucleosides, have been extensively evaluated as cancer-related biomarkers. However, the determination of urinary ribonucleosides is still a challenge due to their low abundance, high polarity and serious matrix interferences in urine samples. In this study, a derivatization method based on a chemical reaction between ribonucleosides and acetone to form acetonides was developed for the determination of urinary ribonucleosides. The derivative products, acetonides, were detected by using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The methodological evaluation was performed by quantifying four nucleosides for linear range, average recovery, precision, accuracy and stability. The validated procedures were applied to screen modified ribonucleosides in urine samples. Improvement of separation and enhancement of sensitivity were obtained in the analysis. To identify ribonucleosides, inexpensive isotope labeling acetone (acetone-d₆) and label-free acetone were applied to form ordinary and deuterated acetonides, respectively. The two groups of samples were separated with orthogonal partial least squares (OPLS). The ordinary and deuterated pairs of acetonides were symmetrically distributed in the S-plot for easy and visual signal identification. After structural confirmation, a total of 56 ribonucleosides were detected, 52 of which were modified ribonucleosides. The application of derivatization, deuterium-labeling and multivariate statistical analysis offers a new option for selective detection of ribonucleosides in biological samples.     

α-Picolinic acid and quinaldinic acid in the separation and volumetric determination of palladium

Analytical and Bioanalytical Chemistry - Palladium can be determined volumetrically after separation with α-picolinic or quinaldinic acid by dissolving the complex in an excess of standard...     

Development of a green stability-indicating HPLC–DAD method for the determination of donepezil hydrochloride in the presence of its related substance and degradation products

A simple, eco-friendly, stability-indicating HPLC method was developed for the determination of donepezil hydrochloride (DH) in tablet dosage form in the presence of its pharmacopoeia-related compound (donepezil-related compound A) and its different degradation products. The chromatographic conditions were optimized to achieve the highest performance parameters using Zorbax Eclipse Plus C18 rapid resolution column (4.6?×?100?mm, 3.5?µm), with a mobile phase composed of 72.5% acetate buffer pH 5.5 and 27.5% ethanol, flowing at 1?mL?min^?1. The diode array detector (DAD) was set at 315?nm and the column oven was adjusted at 45°C. Linear response (r?=?0.9999) was observed over the range of 2–28?µg?mL^?1 of donepezil, with detection and quantitation limits of 0.031 and 0.103?µg?mL^?1, respectively. Forced degradation studies were performed on standard DH and test Demepezil® 5-mg tablets under various conditions and the method was found to be stability indicating. The purity of DH peak was confirmed using the DAD. In the developed method, two principles of green chromatography were adopted (reduce and replace) by reducing solvent consumption through the utilization of a short column (10?cm) with a smaller particle size (3.5?µm) instead of a normal 25?cm with a 5?µm particle size and by replacing hazardous solvents of the official United States Pharmacopoeia method as acetonitrile with ethanol. Furthermore, the greenness of the method was assessed using three assessment tools.     

Copper methanesulfonate-acetic acid as a novel catalytic system for tetrahydropyranylation of alcohols and phenols

A synergistic catalytic effect between copper methanesulfonate and acetic acid in tetrahydropyranylation of alcohols and phenol at room temperature under solvent free condition has been described. Both alcohols (primary, secondary and tertiary) and phenols reacted with 3,4-dihydro-2H-pyran smoothly to afford the corresponding tetrahydropyranyl ethers in good yields.     

Reactions of areneselenenamides with alkenes in the presence of phosphorus(V) and sulfur(IV) oxyhalides. New synthesis of β-haloalkyl selenides

A new procedure was proposed for activation of areneselenenamides with phosphorus(V) and sulfur(IV) oxyhalides. According to the ¹H, ¹³C, and ³¹P NMR data, areneselenenamide reacts with phosphorus oxyhalide to form intermediate adduct in which the phosphorus atom is coordinated at the selenium. Areneselenenamides activated by phosphorus(V) oxyhalides react with alkenes (norbornene and norbornadiene) with high trans-stereoselectivity. Their reactions with terminal olefins are regioselective, and they lead to preferential formation of the corresponding Markovnikov adducts.     

Validation of a novel derivatization method for GC–ECD determination of acrylamide in food

This paper proposes a new method for quantitative analysis of acrylamide in cereal-based foods and potato chips. The method uses reaction with trifluoroacetic anhydride, and analyses the resulting derivative by use of gas chromatography with electron-capture detection (GC–ECD). The effects of derivatization conditions, including temperature, reaction time, and catalyst, on the acylation reaction were evaluated. Chromatographic analysis was performed on an SE-54 capillary column. Under the optimum conditions, good retention and peak response were achieved for the acrylamide derivative. The analytical method was fully validated by assessment of LODs and LOQs (1 ng g^?1 and 25 ng g^?1, with relative standard deviations (RSD) 2.1 and 3.6, respectively), linearity (R?=?0.9935 over the range 0.03–10 μg g^?1), and extraction recovery (>96 %, with RSD below 2.0, for acrylamide spiked at 1, 20, 50, and 100 ng g^?1; 99.8 % for acrylamide content >1000 ng g^?1). The method requires no clean-up of the acrylamide derivative before injection. The method has been successfully used to determine acrylamide levels in different commercial cereal-based foods, French fries, and potato chips.

Is microwave digestion using TFM vessels a suitable preparation method for Pt determination in biological samples by adsorptive cathodic stripping voltammetry?

The occurrence of Pt in environmental matrices is increasing since the introduction of automobile catalytic converters. Given that Pt is bioavailable and causes biological effects in plants and animals, respective biomonitoring programs are in high demand. But the analytical methods for conducting such programs have not yet been sufficiently established. Therefore, a study was carried out to develop a microwave digestion of biological samples, which allows a rapid determination of Pt by adsorptive cathodic stripping voltammetry.A high pressure microwave system was used and the digestion was performed in HNO₃ and HCl. After digestion the HNO₃ was evaporated with a microwave assisted vacuum concentration set. The study resulted in a procedural detection limit of 37.5 ng L⁻¹ and a relative standard deviation of 18%. A recovery study resulted in a Pt loss below 5%. The microwave assisted evaporation of HNO₃ performed satisfactorily and up to 500 mL of the sample solution could be used for the voltammetric measurements without any effect on the peak heights. A direct comparison of Pt concentrations conducted after microwave digestion and digestion by high pressure ashing showed similar values. However, these promising results were not persistent throughout the repeated analysis using the same Teflon vessels. The vessels did not endure the harsh conditions and due to aging processes the Pt loss consistently increased until Pt determination in environmental relevant concentrations became impossible. Quartz vessels could not be employed as an alternative to the Teflon vessels, due to a lack of compatibility with the vacuum concentration system. Consequently, the results of this paper show that there is a need for further development of more resistant Teflon materials.     

Synthesis and characterization of a novel η 2-iminoacyl monocyclopentadienyl titanium(IV) complex

An unusual complex, [CpTi(η²-(C,N)-2-ArNH–C₆H₄C=NAr)Cl₂] (Ar?=?2,6- ⁱ Pr₂C₆H₃) (1) has been synthesized and characterized by elemental analysis, NMR spectra, and single crystal X-ray diffraction. The ¹³C NMR resonance of the imine carbon atom of 1 at δ?221?ppm is consistent with the η²-(C,N) binding. This was confirmed by single crystal X-ray diffraction study of 1. In the complex, Ti atom is five-coordinate with a η²-bound iminoacyl ligand and one Cp ligand occupying the axial position in a distorted square pyramid.     

Development and validation of HPLC method for the determination of α-tocopherol in human erythrocytes for clinical applications

In this work, a simple isocratic reversed-phase HPLC method for determination of alpha-tocopherol in human erythrocytes has been developed and validated. After separation of plasma the erythrocytes were washed three times with 0.9% sodium chloride containing 0.01% butylated hydroxytoluene (BHT) as antioxidant and then were diluted 1:1 (v/v) with the same solution. In the liquid-liquid extraction (LLE) procedure, 2500 microL of n-hexane was added to 500 microL of erythrocytes. After 2 min this mixture was deproteinized by addition of cool ethanol (500 microL, 5 min) denatured with 5% methanol containing alpha-tocopherol acetate (20 micromol L(-1)), as internal standard, and then extracted for 5 min by vortex mixing. After centrifugation (10 min, 1600xg) an aliquot (2000 microL) of the clean extract was separated and evaporated under nitrogen. The residue was dissolved in 400 microL methanol and analysed by reversed-phase HPLC on a 4.6 mmx150 mm, 5 microm Pecosphere C18 column; the mobile phase was 100% methanol, flow rate 1.2 mL min(-1). The volume injected was 100 microL and detection was by diode-array detector at a wavelength of 295 nm. The extraction recovery of alpha-tocopherol from human erythrocytes was 100.0+/-2.0%. The detection limit was 0.1 micromol L(-1) and a linear calibration plot was obtained in the concentration range 0.5-20.0 micromol L(-1). Within determination precision was 5.2% RSD (n=10), between determination precision was 6.1% RSD (n=10). The method was applied successfully in a clinical study of patients with acute pancreatitis and for determination of the reference values in the healthy Czech population.