M. K. Beklemishev

Sorption–catalytic testing of copper on a paper-based sorbent with attached alkylamino groups

Copper(II) was preconcentrated from aqueous solution on paper filters with chemically attached hexamethylenediamino (HMDA) groups and determined directly on the filters by its catalytic action in the oxidation of hydroquinone with H2O2 in the presence of 2,2′-dipyridyl; the reaction was monitored by measuring the absorbance of wet filters. The linear calibration graph of absorbance at 5 min versus log cCu permits the semiquantitative determination of CuII over the range 1 × 10–6–0.1 mg l–1 for a sample volume of 10 ml. Tolerance ratios for foreign ions are 3–4 orders of magnitude more favorable in the hybrid sorption–catalytic procedure than those for the catalytic determination of copper in solution without preconcentration. The procedure is simple and does not require any expensive instrumentation. Samples of tap and sea-water were analyzed.

Synthesis and investigation of isomeric mono- and dinitro derivatives of 3-methyl-4-(pyrazol-3-yl)furazan

The regioselective introduction of nitro groups in pyrazoles, containing a furazanyl substituent at position 3(5) was investigated. All synthetically accessible isomeric mono- and dinitropyrazole derivatives were obtained. X-ray structural investigation was performed for all mononitroisomers and a dinitro derivative.

A Highly Permeable Membrane for Separation of Quercetin Obtained by Nickel(II) Ion-Mediated Molecular Imprinting

A polymer membrane imprinted with quercetin has been synthesized in the presence of nickel(II) acetate as a metal ion mediator. A mixture of methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA), tetrahydrofuran (THF) – methanol (3:1 v/v) as a solvent and Darocur® 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one) as a photoinitiator was polymerized on a track-etched membrane (pores 0.4 µm) used as a support. The polymer formed regular layers on both sides of the membrane and filled the pores. The highest initial flux of the template of 1.8 · 10−7 mol · cm−2 · h−1 was observed for its diffusion from THF/acetate buffer (20:80, v/v) into THF. Membranes polymerized with nickel(II) were both more permeable and more selective. The maximum selectivity factors, calculated by using percent permeation, were 4.5 (quercetin/rutin) and 4.9 (quercetin/naringenin).

Determination of benzoate by paper chromatography with visualization due to its inhibitory activity in the reaction of the photosensitized autooxidation of pyrogallol A

The oxidation of 1,2,4-triacetoxybenzene (Pyrogallol A) and 3,3′,5,5′-tetramethylbenzydine by air oxygen in presence of tris-(2,2′-dipyridyl)ruthenium(II) as a photosensitizer is studied upon irradiation by visible light. The photooxidation of pyrogallol A was inhibited selectively by benzoate at pH 9–11. The rate of the reaction was not affected by other carboxylic acids but was influenced by short-chained aliphatic amines and transition metals. We developed a semiquantitative procedure for the determination of benzoate by paper chromatography. Therein, a common solution of pyrogallol A and a photosensitizer were used for the visualization followed by irradiation with an incandescent bulb. Benzoate was detected as a light spot with Rf ∼ 0.3 against a brown background. The measurement of reflectance intensity for the spot by reflectometry allowed the determination of 1 × 10−5–0.01 M benzoate within a precision of half-order of magnitude. The procedure was validated by comparison to the data of capillary electrophoresis and used to test beverages containing benzoate at levels of 10−4–10−3 M.

Determination of glucose by a kinetic method on a thin-layer chromatogram using the oxidation of 3,3′,5,5′-tetramethylbenzidine with hydrogen peroxide

The oxidation of 3,3′,5,5′-tetramethylbenzidine with hydrogen peroxide in aqueous solutions in the presence of iron(II, III) was studied on the surface of chromatography paper and TLC plates following the general approach to the purposeful selection of indicator reactions in kinetic methods of analysis. Among the 17 studied model analytes, the strongest inhibitory activity was detected for benzoic acid and glucose. The inhibitory effect of substances is likely due to their interaction with hydroxyl radicals forming in the indicator reaction. The most intense signal of glucose was detected on the surface of silica. Glucose was detected as a light spot against the blue background (Rf ∼ 0.5). A procedure for the semiquantitative determination of glucose on a thin-layer chromatogram based on the dependence of the reflectometer-registered value of the reflectance coefficient on the logarithm of the analyte concentration is proposed. In the range 3 × 10−5–0.01 M, two concentrations of glucose differing by one half order of magnitude can be distinguished. The detection limit is 1 × 10−5 M. The procedure was applied to the determination of glucose in beverages, saliva samples, and in a fructose preparation.

Kinetic methods for determining water-soluble polymers

The effect of synthetic water-soluble polymers on the reactions of hydroquinone or 3,3′,5,5′-tetramethylbenzidine periodate oxidation with hydrogen peroxide is studied. A polymer solution was introduced into the reaction and a change in its rate was detected by photometry. Possible reasons for the effect of polymers are discussed, the role of the positive and negative charges of the polymeric chain and the nature of the indicator reaction are considered. The possibility of determining polyelectrolytes by their accelerating and inhibiting effect is demonstrated, including that, under the conditions of polyelectrolyte complex formation, and also by binding with a metal ion catalyzing the indicator reaction. Procedures are proposed for the simple and rapid determination of 3,6-ionene, polyanetholesulfonic acid, polyhexamethyleneguanidine (∼10−5 to 10−4 M, in terms of the monomer), polyethyleneimine and chitosans (∼10−7−10−6 M in terms of the monomer) in aqueous solutions, and also of polyethyleneimine by carrying out the indicator reaction on a silica surface (4 × 10−6 to 0.7 M in terms of the monomer).

Accelerating effect of silica on the indicator reaction o-dianisidine–H2O2

Reaction of oxidation of o-dianisidine (o-D) with H(2)O(2) which is widely used in catalytic methods of analysis in solution has been conducted on silica plates for thin-layer chromatography. The rate of the reaction catalyzed by model compounds (p-toluenesulphonyl chloride, methyl benzoate, benzoic acid, and acrylamide) is noticeably higher on silica than in solution in comparable conditions. The degree of acceleration varies depending on the catalyst and is more pronounced at its lower concentrations. By use of p-toluenesulphonyl chloride determination as an example it has been shown that the accelerating effect of silica enables to decrease the detection limit down to 0.07 nmol cm(-2) (as compared with 4 nmol.cm(-2) in solution); the accuracy is not diminished. It is concluded that catalytic indicator reactions on solid supports may represent high interest for analytical chemists.

Determination of copper by its catalytic effect on the oxidation of hydroquinone by hydrogen peroxide on supports

The reaction of oxidation of hydroquinone by hydrogen peroxide catalyzed by copper(II) in the presence of 2,2’-dipyridyl is activated by hexamethylenediamino groups that are bonded to the surface of filter paper; additional activating effect is produced by 2,2′-dipyridyl. The introduction of malonic acid dinitrile into the indicator reaction improves the sensitivity of the determination of copper and the contrast of the reaction in solution because of the formation of a blue product. Differently colored compounds are formed on a paper support at different concentrations of copper, which makes it possible to visually distinguish the quantities of copper that differ by an order of magnitude in the range 1 × 10-5-0.5 µg. Quantitative detection is possible in the range 5 × 10-6-0.1 µg (cmin = 3 × 10-6 µg). The concentration of copper (0.2-1.5 µg/mL) is determined in blood serum; the consumption of the sample per one determination is 3 µL

Molecularly imprinted inorganic supports in high-performance liquid chromatography and solid-phase extraction

Selective preconcentration of analytes or groups of similar analytes is often useful in the analysis of biological and environmental samples and other samples of complex composition. The problem of the selective recognition of analytes can be solved using the method of molecular imprinting, which is gaining wide acceptance as an alternative to the use of biological recognition agents, for example antibodies, and favors overcoming the shortcomings inherent to the last named ones. The use of molecularly imprinted materials as adsorbents for solid-phase extraction and high-performance liquid chromatography ensures an increase in the selectivity of analyte determination in complex matrixes. This paper is a review of methods for the preparation of molecular imprints on the surface of inorganic matrixes, including nanostructured ones, and of the applications of these materials to chemical analysis.

Adsorption-catalytic test methods

In the development of a new hybrid adsorption–catalytic method it was shown that the selective adsorption isolation of components can be combined with their catalytic determination directly on the adsorbent. To provide theoretical grounds and find fields of the application of the new method, the effect of the support matrix on the rate of catalytic (enzymatic and indicator) reactions was studied. The changes in the performance characteristics of procedures for determining inorganic and organic substances directly on the adsorbent with respect to those of procedures for determining in solutions were analyzed. It was proved that the development of catalytic test procedures with the visual detection of the analytical signal is expedient.