Xerogels doped with 1-(2-pyridylazo)-2-naphthol and Xylenol Orange: Indicator tubes and indicator powders for determining copper(II) and iron(III) in solution

Silica-based xerogels doped with l-(2-pyrilylazo)-2-naphthol and Xylenol Orange were prepared. The xerogels differ in the specific surface and the reagent concentration. Modified xerogels were used as indicator powders for determining copper(II) and iron(III) using indicator tubes. The effects of the reagent concentration in the indicator powder and its specific surface on the length of the colored zone were studied. Indicator tubes were developed for determining 0.3–300.0 mg/L copper(II) and 1.0–120.0 mg/L iron(III) in solutions. The results of determining copper(II) in plant mineral food and iron(III) in natural waters and ashed milk powder are presented.     

New sorbents and indicator powders for preconcentration and determination of trace metals in liquid samples

Two approaches to immobilize complex-forming analytical reagents (PAN, PAR, Xylenol orange, Brombenzothiazo, Crystal violet, Cadion, and Sulfochlorophenolazorhodanine) for the preparation of new sorbents and indicator powders are suggested: on-line coating of reversed-phase silica gel by reagents or doping of porous sol-gel silica with reagents. The retention of Ag, Cd, Cu(II), Co(II), Fe(III), Mn(II), Ni, Pb, and Zn on the sorbents developed was investigated. Quantitative sorption and desorption conditions were optimized. Procedures for the determination of Cd, Cu(II), Fe(III), Pb, and Zn with flame atomic absorption, spectrophotometric, and diffusion scattering spectrometric detection were elaborated. Detection limits for Cd, Cu(II), Fe(III), Pb, and Zn were 3 μg/L, 6 μg/L, 5 μg/L, 40 μg/L, and 1 μg/L, respectively. The procedures were used for the analysis of various real samples, e.g., natural and waste waters, and food. Received: 17 July 1997 / Revised: 20 January 1998 / Accepted: 5 February 1998     

Silica matrices for embedding of magnetic nanoparticles

This paper presents a study regarding the formation of hybrid gels starting from tetraethyl orthosilicate (TEOS), polyvinyl alcohol (PVA) and 1,3-propanediol (PD) and their thermal evolution to mesoporous silica matrices. The possibility of obtaining homogenously dispersed cobalt ferrite inside the silica matrix starting from (TEOS–PVA–PD–Metal Nitrates) gels was also studied. The formation of the hybrid gels TEOS/PVA/PD with different compositions was studied by FT-IR spectrometry and thermal analysis, in order to evidence the interaction between the diol with the organic and the inorganic polymers. Both thermal analysis and FT-IR spectrometry have evidenced the formation of physical and chemical interaction between polyols and the siloxane network. Elemental mapping performed by SEM-EDX technique evidenced the formation of homogenous hybrids both in the presence of the absence of 1,3-propanediol. SEM images of the powders obtained by annealing the hybrid xerogels at 600 °C have evidenced the formation of mesoporous silica. By thermal treatment of the (TEOS–PVA–PD–Metal Nitrates) gels, 30%CoFe₂O₄/70%SiO₂ (mass percent) nanocomposites uniformly dispersed in silica matrix with characteristic magnetic properties, have been successfully synthesized.     

Fabrics and papers modified with analytical reagents for the test determination of selenium(IV) and tellurium(IV)

It is shown that Malachite Green and Crystal Violet immobilized on viscose fabrics can be used as reagents for the rapid determination of selenium(IV) and tellurium(IV). Selenium is determine by the color intensity of ion associates formed by the reagents with the triiodide ion formed upon the reduction of selenium(IV) with potassium iodide and tellurium, by the color intensity of reagent ion associates with telluromolybdic heteropoly acid. The analytical ranges for selenium and tellurium(IV) were 0.005–0.5 and 0.01–0.1 mg/L upon passing 20 and 100 mL of a test solution through the indicator matrix, respectively. The duration of analysis does not exceed 15–20 min. The relative standard deviation is 50%. Test strips were proposed for determining 0.1–100 mg/L selenium(IV) and 1–1000 mg/L tellurium(IV) by the length of the colored zone. The determination of selenium(IV) is based on the oxidation of 4-nitrophenylgydrazine to its diazonium salt and salt interaction with naphthylamine chemically immobilized on paper with the formation of a red azo compound. The determination of tellurium(IV) is based on its reaction with Bismuthol II immobilized on a paper.     

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.     

Effective preparation of crack-free silica aerogels via ambient drying

Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution (4–10 wt% SiO₂). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm³, and ∼675 m²/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%.     

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.     

New test tools: Benzidine on cellulose and silica gel

Chromogenic reagents based on covalent and non-covalent immobilization of benzidine on cellulose and silica gels have been developed and investigated. New test tools and test methods have been elaborated for the determination of chlorine in the concentration range of 0.05–120 mg/L. Received: 6 August 1997/Revised: 13 January 1998/ Accepted: 12 February 1998     

Highly Porous Silica Monoliths from Ethyl (L)-Lactate Modified Silanes

Summary. A new type of silica precursor was synthesized by (trans)alkoxylation of alkoxy- and chlorosilanes with ethyl (L)-lactate. This novel ethyl lactate modified silane was hydrolyzed and condensed in the presence of a non-ionic surfactant – poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer (P123) – to give monolithic silica gels. The wet gels were dried using two different drying techniques resulting in crack-free monoliths: a) supercritical drying with CO₂ to yield a porous inorganic material and b) surface silylation with trimethylchlorosilane to yield an inorganic–organic nanocomposite material. The obtained porous gels were characterized by different techniques including thermal analysis, nitrogen sorption, and electron microscopy (TEM, SEM).     

Determination of organic acids in alcoholic and nonalcoholic beverages by reversed-phase high-performance liquid chromatography

A procedure for the quantification of 9 organic acids, acetic, formic, citric, tartaric, lactic, malic, succinic, oxalic, and fumaric, in alcoholic and alcohol-free beverages by reversed-phase HPLC on a Pronto-SIL C18 AQ (300 × 3 mm) column (3 μm) with the mobile phase 5 mM Li₂SO₄ (pH 3.00, H₂SO₄) at the rate 0.5 mL/min and conductometry detection. The analytical ranges made 5–200 mg/L for tartaric, malic, lactic and acetic acids, 2–200 mg/L for the citric and fumaric, 10–400 mg/L for succinic, 15–400 for oxalic, and 20–200 for the formic acids, and so the detection limits: 1 mg/L for tartaric, formic, malic and fumaric, 2 mg/L for lactic, acetic and citric, 5 mg/L for succinic, and 10 mg/L for oxalic acids. The analysis of alcoholic beverages takes 30–40 min, and of non-alcoholic ones, 20–30 min; the standard deviation of the results of analyses does not exceed 5%.     

Solid-phase fluorescence in chemical test methods of analysis based on the principles of planar chromatography

Morin immobilized on cellulose matrices was used as a reagent for determining Al, Be, and Zr(IV) by the length of the fluorescent zone on a test strip after its contact with the test solution and by the fluorescence intensity of the reaction zone of the indicator matrix after passing the test solution through it. A test procedure was developed for determining 0.2–200 mg/L Al in potable water using paper test strips sealed in a polymer film. Test procedures were developed for determining 0.0001–1 mg/L Al and 0.00001–0.1 mg/L Be in river water by the intensity of the fluorescent zone on the indicator viscose fabric after passing 100 mL of the test solution through it, using a test facility. The time of analysis was 15–20 min. The relative standard deviation did not exceed 40% in the former case and 60% in the latter case.     

Xerogels doped with phosphomolybdic heteropoly compounds: Indicator tubes and indicator powders for determining hydrazines and tin(II) in solution

Xerogels were prepared on the basis of silicon dioxide and doped with phosphomolybdic heteropoly acid, its ammonium salt, and the Vavele reagent. Reactions of modified xerogels with hydrazines, ascorbic acid, hydroquinone, iodide ion, and iron(II) and tin(II) ions were studied by solid-phase spectrophotometry. It was found that the oxidizing properties of heteropoly compounds enhance when they are included into xerogels. It was found that the formal redox potential of phosphomolybdic acid in xerogel is +0.751 V at pH 3.6. Indicator tubes were proposed for the test determination of 10–80 mg/g tin(II) in reagents used in the synthesis of radiopharmaceutical preparations. Indicator powders and indicator tubes were proposed for the test determination of hydrazines in solution (analytical ranges 0.08-6 mg/L and 0.02-1 mg/L, respectively). Deceased.     

Degradation of textile dyes mediated by plant peroxidases

The peroxidase enzyme from the plants Ipomea palmata (1.003 IU/g of leaf) and Saccharum spontaneum (3.6 IU/g of leaf) can be used as an alternative to the commercial source of horseradish and soybean peroxidase enzyme for the decolorization of textile dyes, mainly azo dyes. Eight textiles dyes currently used by the industry and seven other dyes were selected for decolorization studies at 25–200 mg/L levels using these plant enzymes. The enzymes were purified prior to use by ammonium sulfate precipitation, and ion exchange and gel permeation chromatographic techniques. Peroxidase of S. spontaneum leaf (specific activity of 0.23 IU/mg) could completely degrade Supranol Green and Procion Green HE-4BD (100%) dyes within 1 h, whereas Direct Blue, Procion Brilliant Blue H-7G and Chrysoidine were degraded >70% in 1 h. Peroxidase of Ipomea (I. palmata leaf; specific activity of 0.827 U/mg) degraded 50 mg/L of the dyes Methyl Orange (26%), Crystal Violet (36%), and Supranol Green (68%) in 2–4 h and Brilliant Green 54%), Direct Blue (15%), and Chrysoidine (44%) at the 25 mg/L level in 1 to 2 h of treatment. The Saccharum peroxidase was immobilized on a hydrophobic matrix. Four textile dyes, Procion Navy Blue HER, Procion Brilliant Blue H-7G, Procion Green HE-4BD, and Supranol Green, at an initial concentration of 50 mg/L were completely degraded within 8 h by the enzyme immobilized on the modified polyethylene matrix. The immobilized enzyme was used in a batch reactor for the degradation of Procion Green HE-4BD and the reusability was studied for 15 cycles, and the halflife was found to be 60 h.     

The Production of Ultrafine Silica Powders from Silicon Tetrachloride: Control of the Primary Particle Size

Ultra fine silica powders were prepared by hydrolysis of SiCl₄ using aqueous ammonia solution followed by supercritical drying. Using different methods of combining the SiCl₄ and ammonia solution, to vary the initial and final pH of the solution, large silica powders surface areas (271–905 m²/g), fine average particle diameters (3.5–17) nm and low tapping densities (0.02–0.05 g/cm²) could be prepared. Powders with characteristics similar to pyrogenic silica, and with similar thermal stability at temperatures up to 1000°C, could be produced.     

Simultaneous spectrophotometric determination of Tartrazine, Sunset Yellow and Ponceau 4R in commercial products by partial least squares and principal component regression multivariate calibration methods

Three multivariate calibration methods, partial least squares (PLS-1 and PLS-2) and principal component regression (PCR), were proposed and successfully applied to the simultaneous determination of three dyes, Tartrazine (E-102), Sunset Yellow (E-110) and Ponceau 4R (E-124) in mixtures by ultraviolet-visible absorption spectrophotometry. The designed and optimized training set of calibration was applied to the determination of the three dyes in several synthetic mixtures, containing 1.6–20.0 mg/L of Tartrazine, 3.2–40.0 mg/L of Sunset Yellow and 3.2– 36.0 mg/L of Ponceau 4R. 94.5–105.3% recovery values were obtained. Three commercial foods that contained the three dyes were also satisfactorily analyzed without separation step. The results obtained by the application of the three chemometric approaches in the commercial products are discussed and compared with those obtained by an HPLC method and very similar values were found by all methods. Repeatability and reproducibility studies (with the Student’s and F tests) were achieved over two series of nine standards for each dye, showing no significant differences at the 95% confidence level. Received: 27 October 1997 / Revised: 9 January 1998 / Accepted: 24 January 1998     

Solid-phase fluorescence determination of gallium(III) with morin and lumogallion immobilized on cellulose matrices

It has been demonstrated that the fluorometric test determination of gallium(III) can be performed with morin and lumogallion immobilized on thin-layer cellulose matrices. Test procedures have been developed for the determination of Ga(III) in the range 0.5–90 mg/L by the length of fluorescence zone on a test strip sealed into a polymer film (after its contact with the test solution) in the ranges 0.001–1 and 0.01–1 mg/L with the visual detection of the fluorescence of the indicator matrix with morin and lumogallion, respectively (after passing 100 and 20 mL of a test solution through it), and in the range 0.0001–0.1 mg/L by detecting the fluorescence with a portable fluorimeter.     

Controllable synthesis and micelles preparation of tri-block copolymers from 2,2-dimethyl-trimethylene carbonate and ethylene glycol

Amphiphilic triblock copolymer of poly(2,2-dimethyl-trimethylene carbonate)–poly(ethylene glycol)–poly(2,2-dimethyl trimethylene carbonate) (PDTC–PEG–PDTC) was synthesized by dihydroxyl capped PEG with molecular weight of 1,000, 4,000, and 6,000 in the presence of rare earth tris(2,6-di-tert-butyl-4-methylphenolate)s. The rare earth phenolates/PEG system could prepare triblock copolymer with predictable molecular weights with narrow molecular weight distribution. The polymers were characterized by nuclear magnetic resonance spectroscopy, gel permeation chromotography, and differential scanning calorimetry to confirm the structure. The micelles formed from the amphiphilic triblock copolymer were determined by fluorescence spectrophotometer and dynamic light scattering. The critical micelle concentrations fell in the range of 1.67∼5.25 mg/L. Transmission electron microscopy pictures showed that the micelles possess spherical morphology, and the diameters of micelles in number averaged scale ranged from 20–70 nm. The micelles formed from triblock amphiphilic copolymers were explored as carrier for indomethacin (IND), and they could enhance IND solubility in water dramatically.     

Study on the influence of teos–diol molar ratio on their chemical interaction during the gelation process

Hybrid organic–inorganic materials, silica–diol, were synthesized by the sol–gel process from mixtures of tetraethylorthosilicate (TEOS) and diols: ethylene glycol (HO–CH₂–CH₂–OH) and 1,3 propane diol (HO–CH₂–CH₂–CH₂–OH), in acid catalysis. The gels have been synthesized for a molar ratio H₂O:TEOS = 4:1 and different molar ratios diol/TEOS: 0.25; 0.5; 0.75; 1.0; 1.25 and 1.5. The resulting gels were studied by thermal analysis and FT-IR spectroscopy, in order to evidence the interaction of diols with silica matrix. Thermal analysis indicated that the condensation degree increases with the molar ratio diol/TEOS until a certain value. The thermal decomposition of the organic chains bonded within the silica network in the temperature range 250–320 °C, leaded to a silica matrix with modified morphology. The adsorption–desorption isotherms type is different for the samples with and without diol. Thus, the specific surface areas have values <11 m²/g for the samples without diol and >200 m²/g for the samples with diols, depending on the annealing temperature.     

Structures and chromatographic characteristics of capsule-type silica gels coated with hydrophobic polymers in reversed-phase liquid chromatography

Summary Silicone polymer-coated silica gels modified with octadecyl and octyl groups (S/S-C₁₈, S/S-C₈), or “capsule-type silica gels” were developed as packing materials for reversed-phase liquid chromatography. They were obtained by coating the surface of totally porous silica gel with a homogeneous silicone polymer film, and thereafter modifying the coating polymer with octadecyl or octyl groups. Retaining the advantages of silica-based packings, they show strong resistance of alkali-like organic porous polymeric materials.     

Effect of the structure of copper(II) complexes, adsorbed on the surface of SiO2, on their catalytic activity in ozone decomposition

We describe the composition, structure, and catalytic activity in the reaction of ozone decomposition for copper(II) complexes with acido ligands and immobilized Schiff’s bases (propyl benzaldimine derivatives) that are anchored on silica (silica gel, aerosil). We demonstrate methods for controlling their catalytic activity. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 55–60, January–February, 2006.