Simultaneous Spectrophotometric Determination of Rare-Earth and Transition Elements Using Partial Least-Squares (PLS) Multivariate Calibration

A spectrophotometric method for the simultaneous determination of rare-earth and transition elements in synthetic superconductors, [(La_{1 – x} Eu _x )_1.82Sr_0.18CuO₄], by the use of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as chelating agent was developed. The influence of chemical variables affecting the reaction was studied. A partial least-squares (PLS) multivariate calibration procedure was used to assess the data obtained from several calibration solutions measured over the wavelengths range 400–700 nm. The concentration range for Cu was (1–12) × 10^–6 mol/L, while the range for the rare-earth elements La and Eu was (2–8) × 10^–6 mol/L. The relative errors in the determinations were less than 5% in most cases.     

Radiochemical Neutron Activation Analysis of Rhenium and Ammonium Perrhenate Samples

A procedure for the radiochemical neutron activation analysis of rhenium and ammonium perrhenate samples was developed. The procedure provides the determination of about 30 impurity elements present in concentrations of n× 10^–4to n× 10^–8mass % with RSD of 20–30%. An AV-17 anion exchanger–nitric acid solution system was used, which allows the selective separation of rhenium from a wide variety of elements.     

Reactions of superoxide anion radical with antioxidants and their use in voltammetry

Kinetic parameters were calculated for the electrochemical reduction of oxygen at a glassy-carbon electrode with the generation of superoxide radical anions in a 0.05 M solution of (C₂H₅)₄NI in dimethylformamide in the presence of fat-soluble antioxidants, retinol and -tocopherol. A procedure based on the protonation of the radical anion with antioxidant molecules is proposed for the voltammetric determination of antioxidants to determine milligram amounts of retinol and -tocopherol in model solutions (RSD = 1–2%). The calibration graphs for retinol and -tocopherol are linear in the concentration ranges 9.7 × 10^–5–2.3 × 10^–3 and 6.2 × 10^–4–3.1 × 10^–3 M, respectively. The detection limits for retinol and -tocopherol are 4.8 × 10^–5 and 4.1 × 10 ^–4 M, respectively. The procedure was applied to the determination of the active component (retinol and -tocopherol) in pharmaceuticals.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 56–59.Original Russian Text Copyright © 2005 by Ziyatdinova, Gilmetdinova, Budnikov.     

Neutron activation analysis of CdxHg1-xTe

A procedure has been developed for the analysis of Cd_xHg_1-xTe samples; the elements to be determined /Na, K, Cr, Mn, Cu, Co, Zn, As, La/ are separated by chromatography after neutron activation. The detection limit varies between 1×10^–5% and 5×10^–8%. A comparison of the calculation and semiempirical methods of the screening effect determination has been made.     

Determination of Ionol by Voltammetry and Coulometric Titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10^–4 to 1.0 × 10^–2 M (RSD = 9%) and from 3.0 × 10^–5 to 4.0 × 10^–3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10^–4 and 1.0 × 10^–5 M, respectively. The detection limit in coulometric titration was 20 g/mL.     

Microdialysis sampling and high-performance liquid chromatography with chemiluminescence detection for in-vivo on-line determination and study of the pharmacokinetics of levodopa in blood

A simple, reliable, and reproducible method for in-vivo on-line separation and determination of levodopa has been based on microdialysis then high-performance liquid chromatography with chemiluminescence detection. The perfusate is perfused at a flow rate of 5 L min^–1. The concentration of levodopa in the dialysate is determined on line with a chemiluminescence system. The dialysate sample volume is approximately 20 L. The response of the system is linearly related to the concentration of levodopa in the range 1×10^–8 to 1×10^–6 g mL^–1 (r²=0.9995) with a detection limit (3) of 3×10^–9 g mL^–1 and sample throughput of 12 h^–1; RSD is 2.8% (n=11). The method has been successfully used to study the pharmacokinetics of levodopa in vivo; the values of the pharmacokinetics parameters C_max, AUC_0–t and T_max were 16.60, 20.92 ng mL^–1, and 90 min, respectively.     

Determination of Potassium and Sodium in Nonaqueous Solvents by Stripping Voltammetry in a Radio-Frequency Electromagnetic Field

The effect of a radio-frequency electromagnetic field on the parameters of the analytical signal of potassium and sodium in stripping voltammetry in nonaqueous solvents was studied. Sodium and potassium can be separately determined in a concentration range of 2 × 10^–5–2 × 10^–7 M (RSD = 10–17%) upon the irradiation of the solution with an electromagnetic field of a frequency of 55 MHz. The irradiation efficiency depends on the frequency and the nature of the solvent. The detection limits for potassium and sodium were 8.0 × 10^–8 and 1.0 × 10^–7 M, respectively, in the presence of 0.02 M [(C₄H₉)₄N]I in dimethylformamide at a field frequency of 55 MHz.     

An integrated electrochemical fructose biosensor based on tetrathiafulvalene-modified self-assembled monolayers on gold electrodes

An integrated amperometric fructose biosensor based on a gold electrode (AuE) modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) on which fructose dehydrogenase (FDH) and the mediator tetrathiafulvalene (TTF) are co-immobilized by cross-linking with glutaraldehyde is reported. Variables concerning the behavior of the biosensor were optimized by taking the slope value obtained for the fructose calibration plot in the 0.1–1.0 mM concentration range as a criterion of selection. At an applied potential of +0.20 V, a good repeatability of such slope values (RSD=6.7%, n=10) was obtained with no need to apply a cleaning or pretreatment procedure to the modified electrode. Moreover, results from five different TTF-FDH-MPA-AuEs yielded a RSD of 5.8%. The useful lifetime of one single biosensor was approximately 30 days, exhibiting a 93% of the original response on the 33rd day. A linear calibration graph was obtained for fructose over the 1.0×10^–5–1.0×10^–3 M range, with a limit of detection of 2.4×10^–6 M. The effect of potential interferents was evaluated. The TTF-FDH-MPA-AuE also performed well in the flow-injection mode. The biosensor was used for the determination of fructose in real samples, and the results compared with those provided by using a commercial enzyme test kit.     

Flow injection analysis of gallic acid with inhibited electrochemiluminescence detection

A flow injection (FI)–electrochemiluminescent (ECL) method has been developed for the determination of gallic acid, based on an inhibition effect on the Ru(bpy)₃²⁺/tri-n-propylamine (TPrA) ECL system in pH 8.0 phosphate buffer solution. The method is simple and convenient with a determination limit of 9.0×10^–9 mol/L and a dynamic concentration range of 2×10^–8–2×10^–5 mol/L. The relative standard deviation (RSD) was 1.0% for 1.0×10^–6 mol/L gallic acid (n=11). It was successfully applied to the determination of gallic acid in Chinese proprietary medicine—Jianming Yanhou Pian. The inhibition mechanism proposed for the quenching effect of the gallic acid on the Ru(bpy)₃²⁺/TPrA ECL system was the interaction of electrogenerated Ru(bpy)₃^2+* and o-benzoquinone derivative at the electrode surface. The ECL emission spectra and UV-visible absorption spectra were applied to confirm the mechanism.     

Extraction by reversed micelles of triton N-42 for the spectrophotometric determination of cetyltrimethylammonium bromide

Micellar preconcentration of 1 : 2 associates of Bromophenol Blue with cetyltrimethylammonium bromide is proposed to improve the procedure for the spectrophotometric determination of cationic surfactants. The preconcentration procedure involves quantitative extraction by reversed micelles of Triton N-42 in decane followed by the decomposition of the micellar solution with chloroform. The loss of 10^–7–10^–5 M cetyltrimethylammonium bromide in 5–100-fold preconcentration was not supported by the added-found method (RSD = 3–5%). The determination limit for cetyltrimethylammonium bromide is 2 × 10^–7 M.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 17–21.Original Russian Text Copyright © 2005 by Demidova, Bulavchenko.     

Schnelle coulometrische Mikrobestimmung einzelner Polythionate

Zusammenfassung Das neue Mikrobestimmungsverfahren beruht auf der coulometrischen Titration von S₂O₃ ^2– nach vorheriger Abbaureaktion der Polythionate mit Sulfit bzw. Cyanid. Es werden 10 ml Probelösung (S₄O₆ ^2–: 5 · 10^–5 bis 1 · 10^–3 M; S₅O₆ ^2–; 2,5 · 10^–5 bis 1· 10^–3 M; S₆O₆ ^2–: 1,66 · 10^–5 bis 1 · 10^–3 M) benötigt. Die Titrationskurve wird von einem Schreiber registriert. Die Reproduzierbarkeit der jeweiligen Einzelbestimmung liegt bei VK _p±0,1 bis ± 1,6%.

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Rapid coulometric microdetermination of individual polythionates

The method described is based on the coulometric titration of S₂O₃ ^2– after a preceding degradation of the polythionates with sulphite or cyanide. 10 ml of sample solution are required (S₄O₆ ^2–: 5× 10^–5 to 1×10^–3 M; S₅O₆ ^2– : 2.5×10^–5 to 1×10^–3 M; S₆O₆ ^2–: 1.66×10^–5 to 1×10^–3 M). The titration curve is recorded. The reproducibility of a single determination is VK _p±0.1 to ± 1.6%.

     

Determination of Hydrogen and Oxygen in Chalcogenide Glasses Using a Tandem Laser Mass Reflectron

A procedure was developed for determining hydrogen and oxygen in As–Se and Se–S systems by laser mass spectrometry on a tandem laser mass reflectron. The procedure involves special (both preliminary and in the course of analysis) cleaning of the sample surface with a Q-switched laser. The performance characteristics of the proposed procedure were studied on certified standard reference materials of aluminum alloys, oxygen-doped As₂Se₃, and As₂S₃ with the known absorption at lines of hydrogen-containing impurities. The dependence of the analytical signal on the concentration of gas-forming impurities was linear in the concentration range 10^–5 to 10^–2 mass %. The relative random error of measurements was not worse than 0.21. The detection limit was 8 × 10^–6 mass %.     

Langmuir Aggregation of Thionin on Sodium Dodecyl Sulfate and Its Application

The microphase adsorption–spectral correction (MPASC) technique was applied to the interaction of thioin (TN) with sodium dodecyl sulfate (SDS) at pH 4.56. The synergism mechanism of SDS in solution was analyzed and discussed. The great electrostatic aggregation of TN on SDS obeys Langmuir monolayer adsorption. The property constants of the aggregate were determined and the quantitative determination of the anionic surfactant (AS) in samples was made in the presence of EDTA. Results showed that the large micellar aggregate is (TN–SDS₂)₃₁, the adsorption constant of the monomer aggregate is 1.85 × 10⁵ (18°C), and its molar absorptivity is 4.45 × 10⁶ L mol^–1 cm^–1. For analysis of samples, the recovery is between 94.5 and 111% and the RSD is less than 7.62%.     

Determination of Selenium(IV) by Stripping Voltammetry at a Mercury-Film Electrode

A procedure was proposed for the determination of selenium(IV) by stripping voltammetry on a mercury-film electrode at an electrolysis potential of +0.4 V versus the saturated silver–silver chloride reference electrode in a 1 M H₂SO₄ solution. The current of the cathodic peak is a linear function of the selenium(IV) concentration in the range from 5 × 10^–3 to 3 × 10^–1 mg/L (6.3 × 10^–8 to 3.8 × 10^–6 M) at a time of electrolysis of 30 s (t _el). The detection limit for selenium is 1 × 10^–4 mg/L (1.3 × 10^–9 M) at t _el = 300 s. It was shown that selenium(IV) can be determined in the presence of 10 mg/L Zn(II), 1 mg/L Cd(II), 0.5 mg/L Pb(II), and 0.2 mg/L Cu(II). A procedure for the determination of selenium in natural, mineral, and potable water was proposed.     

Large-Scale Purification of Water-Soluble Polysaccharides from Flaxseed Mucilage, and Isolation of a New Anionic Polymer

Summary Viscous flaxseed mucilage has previously been described as a mixture of two polysaccharides (acidic and neutral). In this study, we have shown that a combination of ion exchange and size exclusion chromatography enables purification of three distinct polysaccharides. Molecular weight (Mw) analysis, performed by size-exclusion chromatography on line with a multi-angle laser light-scattering detector, revealed that the main polysaccharide (75%) was a neutral polymer with a Mw of approximately 1.2 × 10⁶ g mol^–1. The two others were acidic polysaccharides denoted AF₁ (3.75%, 6.5 × 10⁵ g mol^–1) and AF₂ (21.25%, 1.7 × 10⁴ g mol^–1).Presented at: International Symposium on Separation and Characterization of Natural and Synthetic Macromolecules, Amsterdam, The Netherlands, February 5–7, 2003     

Determination of Some Liposoluble Antioxidants by Coulometry and Voltammetry

It is found that the interaction of retinol, ergocalciferol, and cholecalciferol with electrochemically generated bromine proceeds rapidly and quantitatively. The stoichiometric coefficients of the reaction are 1 : 2, 1 : 7, and 1 : 3, respectively. A coulometric determination of microgram amounts of individual liposoluble antioxidants in model solutions was performed with RSD = 1–5%. The voltammetric response of retinol and -tocopherol was studied at a stationary platinum microelectrode in 0.1 M HClO₄ and 0.1 M CH₃COONa in acetonitrile. The quantification limit for -tocopherol is 2.7 × 10^–4 M in 0.1 M HClO₄, and the quantification limits for retinol are 4.1 × 10^–5 M in 0.1 M HClO₄ and 2.1 × 10^–5 M in 0.1 M CH₃COONa. A procedure for the coulometric determination of total free liposoluble antioxidants in human blood serum is proposed.     

Electrochemical Determination of Glutathione

Procedures were developed for determining glutathione by voltammetry and coulometric titration with electrogenerated oxidants using the biamperometric indication of the titration end-point. Possible mechanisms of the glutathione reaction with electrogenerated halogens are discussed. Microgram amounts of glutathione can be determined in model solutions with an RSD of 1–2%. The oxidation wave of glutathione in the voltammogram is observed at 0.95 V. At higher glutathione concentrations, the wave takes the shape of a peak. Glutathione concentration in the range between 9.15 × 10^–5 and 2.14 × 10^–3 M is a linear function of its oxidation wave height at a stationary platinum electrode in a 0.05 M H₂SO₄ solution. The determination limit for glutathione is 1.9 × 10^–5 M. The procedures for determining glutathione in human blood were proposed.     

Catalytic Determination of Trace Amounts of Iridium As Chloride Complexes

A procedure was developed for the determination of iridium as chloride complexes by its catalytic action on the oxidation reaction of Sulfarsazene with potassium periodate at pH 5.6. The analytical range was 1 × 10^–5–1 × 10^–3 g/mL iridium. The accuracy of the procedure developed was confirmed in the determination of iridium in model solutions by the standard addition method. The relative standard deviation did not exceed 6%.     

Sensitive determination of nitrite by means of a Landolt-type reaction in fluorescent aggregates of a binaphthyl-based amphiphile

The iodine quenching effect on the fluorescence of a binaphthyl-based amphiphile, C₈BNC₆N, was used for monitoring the Landolt-type reaction between nitrite, iodide, and thiosulfate. Due to the possibility of iodine detection in the 10^–8–10^–7 M range, and to the effective concentration of anionic reagents on the surface of cationic aggregates, the indicator reaction can be monitored using reagents at concentration levels as low as 10^–7 M. To optimize the analytical system, the effect of pH and reagent concentrations on the rate of indicator reaction were studied. The influence of the matrix of water samples and effect of side-reactions increasing the value of a blank test were examined. A procedure for nitrite determination in water was developed, using the diazo reaction for selective nitrite removal to provide a reference solution, which avoided possible effects of the matrix components. The usefulness of this method was tested by determining trace amounts of nitrite in water samples. The procedure allows determination of nitrite down to 5 ng/ml (detection limit about 2ng/ml) with r.s.d. of 10% in the 20–250 ng/ml range.     

Selective Sorption–Spectrometric Determination of Nanogram Amounts of Vanadium(IV) and Vanadium(V)

Conditions of the selective sorption–spectrometric determination of vanadium(IV) and vanadium(V) using sulfonitrophenol M were found. The determination of vanadium (visual test (RSD = 30%) using a reference color scale or quantitative determination (RSD < 10%) by diffuse reflectance spectra is performed immediately after the dynamic-mode sorption of its colored complexes with sulfonitrophenol M at pH 3.5 (vanadium(IV)) or with sulfonitrophenol M and hydroxylamine at pH 1.5 (vanadium(V), 650 nm) at the surface of polyamide membrane disks (d= 1 cm, l= 0.1 mm, m= 2.7 mg). The flow rate is 10–20 mL/min. The detection limit is 5–7 ng of vanadium in the support zone or 0.2–0.5 ng/mL. The determination of 0.5–5 ng/mL vanadium(V) at pH 1.5 does not interfere with 20-fold amounts of V(IV) and 1000-fold amounts of Ni, Zn, Cd, Mg, Co, Cr(III), Mn, PO^3- ₄, and F^–.