Indicator Tubes and Indicator Powders for Determining Fluoride and Chloride Ions

Noncovalent immobilization of Arsenazo I, Alizarin Red, Xylenol Orange, and diphenylcarbazone by incorporation into silicic acid xerogels and modification of silica gels was studied, and procedures for determining fluoride and chloride ions by solid-phase spectrophotometry and test methods were developed. Reactions of immobilized reagents with aluminum(III), zirconium(IV), and mercury(II) were studied. The possibility of using immobilized reagent–metal ion–halide ion systems for the determination of halide ions was assessed. Indicator powders were proposed for determining 0.5–10 mg/L fluoride ions and 1–30 mg/L chloride ions, and indicator tubes were developed for determining 20–200 mg/L chloride ions. The determination of fluoride and chloride ions is based on exchange complexation reactions proceeding in the systems immobilized Xylenol Orange–zirconium(IV) and immobilized diphenylcarbazone–mercury(II), respectively. Performance characteristics of the developed procedures were estimated. The procedures were verified by determining halide ions in Narzan mineral water.     

Test determination of aniline in solutions based on azo coupling with analytical reagents incorporated into silicic acid xerogels

Silicic acid xerogels modified with 1-naphthol, 2-naphthol, 8-hydroxyquinoline, 2,7-dihydroxynaphthalene,N-(l-napthyl)ethylenediamine andp-hydroxydiphenyl were synthesized. It was shown that the immobilized reagents can participate in reactions of azo coupling with products of aniline diazotization. The best (among the studied) immobilized reagent for determining aniline was 1-naphthol. Xerogel modified with 1-naphthol was used for determining aniline in solutions by solid-phase spectrophotometry and with visual detection. The analytical ranges for aniline at the optimal conditions were 0.005-10 mg/L using solid-phase spectrophotometry and 0.05-15 ng/L with visual detection. The results were verified in the analysis of synthetic mixtures.     

Xerogels modified with l-(2-Pyridylazo)-2-naphthol and dimethylglyoxime: Indicator tubes for determining nickel

A simple and rapid sol-gel method was proposed for preparing xerogels modified with l-(2-pyrilylazo)-2-naphthol and dimethylglyoxime. Reactions between nickel and xerogels modified with l-(2-pyrilylazo)-2-naphthol and dimethylglyoxime were studied by solid-phase spectrophotometry, and the optimal conditions were found. Procedures for determining nickel in solution by solid-phase spectrophotometry and tests based on indicator tubes containing powdered xerogel modified with l-(2-pyrilylazo)-2-naphthol were developed. The analytical ranges for nickel in the above methods were 0.1–2 and 0.2–30 mg/L, respectively. The interference from cobalt(II) was eliminated by its adsorption on hydrophobic C₁₆ and C_phenyl silica gels modified with l-(2-pyrilylazo)-2-naphthol. The interference of copper(II) and iron(III) was eliminated by the addition of a mixture of Na₂S₂O₃ and NH₄F.     

Silica-based xerogels modified with cobalt(III): Determination of naphthols in solutions by solid-phase spectrophotometry

Silica-based xerogels modified with various concentrations of cobalt ions were prepared. The redox and complexing properties of immobilized cobalt ions were studied. Modified xerogels were used for determining naphthols in solutions by solid-phase spectrophotometry after their nitrosation. The effects of various factors on the absorbance of xerogels were studied. These factors are the average pore diameter in powdered xerogels, the concentration of cobalt(III), the pH of the test solution, and the concentration of CH₃COOH and NaNO₂ at the stage of nitrosation. The best conditions for determining naphthols were found. The developed procedure was used in the analysis of various samples.     

Spectrophotometric Methods for Determining Noble Metals

The main trends of the development of spectrophotometric methods for determining noble metals (NMs) are considered. One of these trends is the synthesis and study of new, highly sensitive and selective organic reagents for determining NMs in solutions and in solid phase. Another trend is the search for and development of new methodological approaches (techniques) and color reactions, including those that involve modified and immobilized reagents. The third trend includes the improvement of equipment and automation in FIA, CFA, derivative, rapid-scanning, and multiwavelength spectrophotometry. It also implies a new generation of instruments measuring the absorbance and reflectance of solid materials modified with organic reagents and with their NM complexes; microwave energy sources for the dissolution of samples, preparation of test solutions, and activation of photometric reactions; and multioperational analytical moduli for autoclave sample preparation with resistive heating. The present-day spectrophotometry can provide the determination of NMs in samples with concentrations from several to 10^–4% (photometry and differential photometry) and down to 10^–7% (test and sorption–spectroscopic methods based on photometry and diffuse-reflectance spectroscopy, including the use of chromaticity functions).     

Polarographic and voltammetric determination of trace amounts of 2-nitronaphthalene

The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2×10^–6–1×10^–4, 2×10^–7–1×10^–4, 1×10^–8–1×10^–4 and 2×10^–9–1×10^–8 M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid–liquid and solid-phase extraction with limits of determination of 3×10^–10 M (drinking water) and 3×10^–9 M (river water).     

Determination of Chromium in Natural Water by Stripping Voltammetry

Conditions were optimized for determining microgram amounts of chromium by stripping voltammetry with a modified carbon-paste electrode. The developed procedures were applied to the analysis of different waters. The proposed procedures exhibit high performance characteristics and ensure the determination of 9.6 × 10^–9 to 1.0 × 10^–6 M chromium.     

Determination of Stability Constants of Copper(I) Chelates with 1,10-Phenanthroline by Thermal Lensing

Using investigations of the copper(I)–1,10-phenanthroline system as an example, it is shown that thermal lensing can be used for determining stability constants at a level of concentrations one–two orders of magnitude lower compared to conventional spectrophotometry, with better precision of measurements. The values of stability constants are log₂= 11.7 ± 0.7 without regard for stepwise chelation, and logK ₁= 5.9 ± 0.3, logK ₂= 5.4 ± 0.3, and log₂= 11.3 ± 0.6 taking into account stepwise chelation. It is shown that, when shifting from microgram to nanogram amounts of reactants in the determination of stability constants by thermal lensing, changes in the kinetic parameters of the reaction studied should be taken into account. The thermal-lens limit of detection of copper(I) is 2 × 10^–8M; the linear calibration range is 4 × 10^–8–2 × 10^–5M (488.0 nm, pump power 120 mW). The data obtained were used for determining copper(I) in the hydrogen sulfide layer of the Baltic Sea.     

Determination of cobalt in the presence of high concentrations of zinc by differential pulse polarography

Summary Cobalt(II) can be determined in 0.1 mol/l Na₃citrate + 0.1 mol/l NH₄Cl + 0.08% dimethylglyoxime as supporting electrolyte in the presence of a 50 000-fold excess of zinc by differential pulse polarography. The limit of determination is 4.2×10^–5 mol/l Co (2.5 mg/l). Linear calibration curves are obtained within the range of 1×10^–7 to 5×10^–6 mol/l cobalt without zinc and in the presence of 5×10^–3 mol/l Zn. The analytical method developed is suitable for the determination of cobalt in zinc plant solutions.

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Cobaltbestimmung in Gegenwart hoher Zinkkonzentrationen mit Hilfe der Differential-Puls-Polarographie

     

Simultaneous Determination of Aromatic Amines by Liquid Chromatography Coupled with Carbon Nanotubes/Poly (3-methylthiophene) Modified Dual-Electrode

Liquid chromatography with amperometric detection (LC-AD) is developed and applied to simultaneously determine five aromatic amines. In the LC-AD, a new carbon nanotubes/poly(3-methylthiophene) modified dual-electrode is fabricated and then used as the working electrode. It is found that this chemically modified electrode (CME) exhibits efficiently electrocatalytic oxidation for aromatic amines with relatively high sensitivity, stability and long-life. Thus, lower detection in LC-AD can be achieved, which are 4.0 × 10^–8 mol L^–1 for aniline, 1.6 ×10^–7 mol L^–1 for 4-nitroaniline, 1.0 × 10^–7 mol L^–1 for 4-chloroaniline, 1.5 × 10^–7 mol L^–1 for 1-naphthylamine, 1.7 × 10^–7 mol L^–1 for 2-bromoaniline. The recoveries of the five analytes are also determined, which range between 0.95 and 1.05 for drinking water, 0.86 and 1.10 for the LiWa River water.     

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.     

Internal Polarity of Class I and Class II Type Sol–Gel Hybrid Materials Using Aromatic Aminoketones as Solvatochromic Probes for Adsorbed Solvents and the Silicatic Cage

2-Hydroxyethylamino functionalized aromatic amino ketones bearing furyl and thienyl as well as 4-N, N-dimethylaminophenyl moieties have been used as solvatochromic probes when entrapped physically (Class I) and chemically bonded (Class II), respectively, to silicatic sol–gel hybrid materials. Class I hybrid materials have been obtained by encapsulation the dissolved probe during the acidically induced sol–gel procedure using various amounts of methyltrimethoxysilane and tetramethoxysilane as components. Class II xerogels have been synthesized by functionalization of the 2-hydroxyethylamino substituted aryl ketones with 3-isocyanatopropyltriethoxysilane and subsequent sol–gel process with TEOS (tetraethoxysilane). Molecular structures of the hybrid materials have been confirmed by solid-state MAS CP -²⁹Si and -¹³C NMR spectroscopy.Significant influences of the polarity of adsorbed solvents and of composition of the sol–gel material on the UV/Vis absorption spectrum of the encapsulated solvatochromic moiety are observed.Mobility of the entrapped probe and the associated influence of the adsorbed solvent upon the probe in the pores are significantly different for the two different classes of sol–gel materials studied.Solvatochromism of Class I xerogels shows that opposite effects of primary alcohols as function of alkyl chain length on the interfacial polarity are observed. They are caused by the influence of the internal surface modified with the solvent and origin solvent polarity on the UV/Vis spectrum of the encapsulated probe. Class II xerogels show related effects as observed for the probes studied in well behaved regular solvents.     

Linear scan stripping voltammetry of copper(II) at the chemically modified carbon paste electrode

A new chemically modified electrode (CME), -benzoinoxime (CUPRON) modified carbon paste electrode, for determining copper(II) is reported because of its excellent selectivity and sensitivity. The electrode is made by mixing a quantity of CUPRON (25%, w/w) with graphite powder (50%, w/w) and paraffin oil (25%, w/w). The CME preferentially deposits copper from the pH 8.5 NH₃-NH₄Cl buffer solution containing copper(II) under an open circuit and most of metal ions do not interfere with the measurements. The detection limit (S/N of three) for determining Cu(II) is 3 × 10^–10 g/ml after 10 min accumulation in fast linear scan stripping voltammetric measurement. Linear calibration curves are obtained for Cu(II) concentration ranged from 1 × 10^–8 M to 1 × 10^–6 M. The response can be maintained with relative standard deviation of 6.0% in a 5 × 10^–6 M Cu(II) solution after eight accumulation/measurement/ regeneration cycles at the same electrode surface. The effect resulted from carbon paste preparation, reduction potential, electrode renewal, electrolyte and solution pH, preconcentration time, concentration dependence, possible interference and other variables has been evaluated. As for application, the CME demonstrates its high sensitivity and copper-selectivity in complex composition samples, such as anodic mud and polluted water.     

The electrochemistry and determination of Ligustrazine hydrochloride

Ligustrazine is one of the active ingredients contained in Ligusticum chuanxiong Hort. (Umbelliferae), which is widely used in traditional Chinese medicine for the treatment of cardiovascular problems. In this work, the electrochemistry of Ligustrazine hydrochloride (LZC) and its determination are investigated. The detection limit is estimated to be 8.0×10^–8 M, with three linear ranges from 1.0×10^–6 to 1.0×10^–4 M, 1.0×10^–4 to 5.0×10^–4 M, and 6.5×10^–4 to 1.6×10^–3 M. The method has been proved to be highly sensitive, selective, and stable, and has been successfully applied to determining LZC in LZC injections.     

Cobalt Hexacyanoferrate-Modified Electrode for Amperometric Assay of Hydrazine

A graphite electrode modified with cobalt hexacyanoferrate by mechanical immobilization was used for amperometric determination of hydrazine. The modified electrode exhibits good catalytic activity for the oxidation of hydrazine at a reduced overpotential with remarkable sensitivity. The modified electrode showed a linear response for hydrazine in the concentration range of 2.0 × 10^–5 to 2.8 × 10^–4 M. The detection limit was 9.8 × 10^–6 M (S/N = 3). The proposed modified electrode was simple, sensitive, rapid, stable and promising.     

Electrochemical Preconcentration of Arsenic(III) in Its Determination by Stripping Voltammetry at Graphite Electrodes Modified with Gold and Copper

The effect of some factors (potential and time of electrolysis, nature and concentration of supporting electrolyte) on the electrochemical preconcentration of arsenic at graphite electrodes modified with copper and gold adatoms was studied. The data obtained were used for the determination of 10^–7to 10^–6M arsenic(III) by stripping voltammetry. The detection limits for arsenic using graphite electrodes modified with copper and gold were 6.3 × 10^–7and 2.3 × 10^–7M, respectively.     

A kinetic method for the determination of zinc(II) in presence of a large excess of cadmium(II) by the different dissociation rate of their complexes with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine

Summary Acid-dissociation reaction of the cadmium(II) complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphme (H₂tspp) proceeds about 10¹² times as fast as that of the zinc(II) complex. This provides the basis for a kinetic determination of zinc(II) in presence of a large excess of cadmium (II). The absorbance at soret-band (421 nm) of Zn(II)(tspp) was used to monitor the reaction. At 5.0×10^–2 M hydrogen ion concentration, Cd(II)(tspp) dissociates completely to Cd²⁺ in 1 s and only the reaction associated with Zn(II)(tspp) is observed during the reaction time from 30 s to 5 min. Zinc(II) concentration <10^–6 M is determined in the presence of 10^–2 M cadmium(II). The molar absorption coefficient is 2.7×10⁵ M ^–1 cm^–1. Iron(III), aluminum(III) and cobalt(II) being masked sodium tartrate, this method is highly selective and is free from interferences of most substances usually encountered. The method was applied to determine zinc(II) in tap water and in cadmium(II) sulfate.     

Indirect spectrophotometric determination of fluoride using the ternary system: Thorium-chrome azurol S-cetyltrimethylammonium

Summary The conditions for the reactions of fluoride with the ternary Th-CAS-CTA/CP/zeph and Th-ECR-CTA complexes have been examined, and a new, sensitive and precise method based on the Th-CAS-CTA-F^– system developed for the indirect determination of fluoride. The molar absorptivity of the method is extremely high —10.0× 10⁴l·mole^–1·cm^–1 at 635 nm (in the others, frequently used, spectrophotometric methods for determining fluoride, does not exceed 2.7×10⁴, e. g. for the method with Alizarin Complexone —1.4×10⁴ and with zirconium and Eriochrome Cyanine R— 2.7×10⁴). Beer's law is obeyed up to a fluoride concentration up to 0.08g per ml. The precision and accuracy of the method were tested in analysis of tap water.

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Indirekte spektrophotometrische Bestimmung von Fluorid mit Hilfe des Systems Thorium-Chromazurol S-Cetyltrimethylammonium

Zusammenfassung Die Bedingungen für die Umsetzung von Fluorid mit den ternären Komplexen Th-CAS-CTA(CP)zeph und Th-ECR-CTA wurden geprüft und eine neue, empfindliche und genaue Methode für die indirekte Fluoridbestimmung ausgearbeitet, die auf dem System Th-CAS-CTA-F^– beruht. Dessen molare Absorptivität ist sehr groß: 10,0×10⁴l·mol^–1·cm^–1 bei 635 nm. (Bei den üblichen spektrophotometrischen Methoden zur Fluoridbestimmung ist nicht größer als 2,7×10⁴ bei der Methode mit Zr und Eriochromcyanin bzw. 1,4×10⁴ bei der Methode mit Alizarin-Komplexon). Das Beersche Gesetz gilt bis zu 0,08g Fluorid/ml. Die Genauigkeit des Verfahrens wurde mit Analysen von Leitungswasser geprüft.

     

Electrochemical behavior of dopamine at a quercetin-SAM-modified gold electrode and analytical application

A stable quercetin–thioglycolic acid-modified gold electrode (Qu–TCA/Au) was prepared as a self-assembled monolayer (SAM) and its electrochemical behavior was investigated by electrochemical methods. In 0.05-M phosphate buffer solution (pH 7.0) quercetin exhibits quasi-reversible signals at the Qu–TCA/Au electrode. The stability of the quercetin-modified gold electrode is very good. The quercetin self-assembled monolayer is an effective mediator for the oxidation of dopamine, which was investigated by cyclic voltammetry and differential pulse voltammetry. Ascorbic acid does not interfere with determination of dopamine at an electrode modified with a mixture of quercetin–thioglycolic acid and quercetin–11-mercaptoundecanoic acid. This modification allows dopamine to be determined in the presence of ascorbic acid in the range from 3×10^–5 to 3×10^–4 M. The detection limit is 1×10^–6 M. Scanning electrochemical microscopy (SECM) was employed to study the electrochemical performances of the modified gold electrode indicating different feedback modes at differently modified surfaces.