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Stoichiometry and stability of electron donor–acceptor complexes formed by dibenzothiophene and its alkylated derivatives with DDQ and TCNE in nonpolar organic solvents has been investigated. 4,6-Dimethyldibenzothiophene produces the most stable 1: 1 complex with DDQ in agreement with energy levels of the π-donors HOMOs and π-acceptors LUMOs calculated by DFT. The results make possible an employment of the complexes for multiplex determination of polycyclic aromatic pollutants using surface enhanced Raman spectroscopy.

Toxic, carcinogenic, and mutagenic properties of polycyclic aromatic hydrocarbons (PAHs) and environmental pollution caused by polycyclic aromatic sulfur heterocycles (PASHs) postulate the importan...

A unique approach based on Molecular Immobilization and Resonant Raman Amplification by Complex-Loaded Enhancers (MIRRACLE) on copper (II)-chitosan-modified SERS-active metallic nanostructured substrates is proposed for sensitive and rapid determination of the catecholamines (CA) dopamine, norepinephrine, and epinephrine. The ternary (CA)

Solid-phase extraction of polycyclic aromatic sulfur heterocycles (PASHs) and their rapid determination in oil fuel without tedious sample pretreatment are of high interest. We propose porous and optically transparent hydrogels prepared from the covalently crosslinked chitosan (CS) as the basis for a sensor system for the rapid and robust monitoring of PASHs. We efficiently combined the ability of the crosslinked CS to sorb PASHs, the capacity of microcavities in a molecularly imprinted polymer to selectively recognize and trap analytes, and the optical transparency of CS materials for selective sorption and solid-phase fluorometric determination of dibenzothiophenes. For the screening of PASHs in organic nonpolar media, ortho-phtalic dialdehyde appeared to be the most appropriate crosslinker. Synthetic and analytical procedures performed in microplate mode allowed obtaining CS hydrogels with suitable reproducible properties and their further time- and labor-efficient applying in analysis (particularly, as little as 2 μM dibenzothiophene oxide can be determined).

Toxic, carcinogenic, and mutagenic properties of polycyclic aromatic hydrocarbons (PAHs) and environmental pollution caused by polycyclic aromatic sulfur heterocycles (PASHs) postulate the importance of their selective and sensitive determination in environmental and oil fuel samples. Surface-enhanced Raman spectroscopy (SERS) opens up an avenue toward multiplex analysis of complex mixtures, however not every molecule gives high enhancement factors and, thus, cannot be reliably detected

A sensitive, rapid, and simple fluorimetric procedure for the determination of artemisinin in a concentration range of 0.1–7 μM was developed with the use of microperoxidase-11 as a peroxidase biomimetic (RSD = 0.8% at LOQ, n = 5; LOD = 7.1 nM (3s0)). The determination is based on the fluorescence quenching of the cationic xanthene dye pyronin B (Stern–Volmer quenching constant, 0.101 μM–1) in the presence of microperoxidase-11. The procedure was tested in the analysis of a biologically active additive based on an Artemisia annua wormwood extract. The correctness of the results of the fluorimetric determination of artemisinin in a biologically active dietary supplement was confirmed by HPLC–mass spectrometry. The use of oligopeptide microperoxidase-11 instead of heme-containing proteins (hemoglobin, cytochrome c, and horseradish peroxidase) made it possible to shorten the duration of artemisinin determination by a factor of 2 with the retention of sensitivity and selectivity.

The review summarizes authors’ works of the last 15 year covering the possibilities, advantages, and prospects for the use of optical sensors based on peroxidase for the determination of a wide range of biologically active compounds, i.e., phenolic compounds and hydroperoxides of different structures, phenothiazines, catecholamines, and their metabolites, for the quality control of drugs, foodstuffs, biomedical research, and clinical diagnostics.

The review concerns the state of the art, the advances in and prospects for application of surface-enhanced Raman spectroscopy (SERS) in chemical analysis. Key advantages (nondestructive origin, high sensitivity and selectivity, easiness of sample preparation) and drawbacks (a relatively small number of analytes, insufficient metrological characteristics of certain objects) of the method are pointed out. Particular attention is paid to the development of novel chemical approaches and to the design of versatile optical sensors to significantly enhance the analytical potential of the method and to extend the range of analytes. Examples are given of the application of SERS in key branches of science and technology that require both qualitative and quantitative chemical analysis of complex objects, viz., environmental monitoring, fuel and energy area, medical diagnosis, biology and biochemistry. The bibliography includes 502 references.

In this work, the first use of a cellulose hydrogel film reconstituted from ionic liquid (IL) 1-butyl-3-methylimidazolium chloride for the fluorescent determination of a plant antimalarial endopero...

A novel concept of advanced SERS (surface enhanced Raman spectroscopy) planar sensors is suggested for fast analysis of sulfur-containing hazardous oil components and persistent pollutants. The main advantage of the proposed sensors is the utilization of an additional preconcentrating layer of optically transparent chitosan gel, which is chemically modified with appropriate π-acceptor compounds to selectively form charge-transfer complexes (CTCs) at the interface with nanostructured silver coatings. The CTCs shift absorption bands of polycyclic aromatic sulfur heterocycles (PASHs) and other important analytes in a controllable way and thus provide a surplus enhancement of vibration modes due to resonant Raman scattering. This novel indicator system provides multiplex determination of PASHs in different forms in a small volume of oil without any tedious sample pretreatment steps. This approach opens new possibilities of increasing either spectral and concentration sensitivity or specificity of SERS-based sensors, allowing for new developments in the fields of ecology, advanced fuel analysis, and other prospective applications.

New ternary complexes of europium with oxytetracycline possessing the intense fluorescence have been obtained for prospective applications in the high-sensitive detection of biogenic amines and their metabolites in biological fluids. Their stability constants have been determined using the Foster–Hammick–Wardley method based on the fluorescent spectroscopy data. The dependence between structure differences, stability constants of ternary complexes of europium–oxytetracycline with biogenic amines, and their metabolites, and sensitivity of their determination has been established.

To evaluate new applications of cellulose hydrogel films prepared via the dissolution-regeneration of microcrystalline cellulose in two hydrophilic ionic liquids – 1-butyl-3-methylimidazolium acetate (BmimAc) and chloride (BmimCl), their optical, mechanical, and adsorption properties were concurrently studied and compared for the first time. The mild conditions under which both films were optically transparent and easy to handle were found. The BmimAc-reconstituted films exhibited an increased tensile strength and elongation at break of 9.5 and 2.5 times, respectively, than the BmimCl-reconstituted films. Due to the sponge-like morphology of the surface, BmimAc-reconstituted films demonstrate enhanced adsorption ability with respect to indigo carmine that is widely applied for industrial needs. This finding opens up opportunities for their use as an adsorbent for dyes. BmimCl-reconstituted films appeared to be a more promising material for the noncovalent immobilization of pyronin B, which is a component of the optical indicator systems for detecting different biologically active compounds.

The expedience of the target-specific control of the properties of a medium (using micellar and aqueous–organic media), in which an indicator process providing the background for the operation of a spectrophotometric sensor based on a polyelectrolyte complex (horseradish peroxidase–chitosan) is conducted, is shown experimentally and proved by calculations of kinetic parameters of the enzymatic reaction. The application of the sensor ensures an increase in the sensitivity of the determination of peroxides of different nature and structures (e.g., hydrogen and urea peroxides, benzoyl peroxide, 2-butanone peroxide and tertbutyl hydroperoxide) in complex matrixes. The proposed approach allows the analyst not only to regulate the performance characteristics of the developed procedures for the determination of peroxides depending on the analytical task, but also to extend the range of test samples (including those insoluble in water) analyzed with no sample preparation.

The kinetics of guaiacol oxidation by hydrogen peroxide and tert-butyl hydroperoxide catalyzed by horseradish and soybean peroxidases in the presence of 1-butyl-3-methylimidazolium acetate and tet-rafluoroborates of 1-butyl-3-methylimidazolium and N-butyl-4-methylpyridinium are studied and compared. The inhibiting effect of acetate ionic liquid on both peroxidases that occurred via the noncompetitive type is found; the Michaelis and inhibition constants have been calculated. Causes of different degrees of inhibition of the catalytic activity of plant peroxidases by ionic liquids are discussed. The advantages of their application compared to the polar molecular organic solvents are demonstrated.

The literature data published in 1993–2012 on the development and application of optical sensors for the determination of phenolic compounds of various structures are summarized. The design, analytical characteristics, and advantages and disadvantages of the existing optical sensors are reviewed, and some examples of using optical sensors in the analysis of real samples, including those from field experiments, are considered in detail.

Up-to-date information on the microbiological method of fuel desulfurization has been systematized and the ways of increasing the efficiency of this method have been considered. The prospective uses of biochemical methods for the specific elimination of sulfur from petroleum and the production of fuel conforming to modern standards are discussed. Reports on the novel desulfurization procedure that employs commercial preparations of enzymes and proteins are analyzed in detail.

It was shown that the sensitivity of the determination of phenolic compounds using chitosan-based optical biosensors could be increased by varying the sorption conditions of products of enzymatic oxidation of phenolic compounds. Sorption isotherms of oxidation products of phenolic compounds by a chitosan film were studied according to Langmuir and Freundlich models. Quantitative characteristics of the sortpion process, such as maximum sorption capacity, the Langmuir isotherm constants, and the Gibbs free energy were determined.

The review considers the prospects of using molecular recognition by artificial receptors (macro-cyclic compounds and molecularly imprinted polymers) to create sensors for the determination of biologically active compounds, i.e., substrates of oxidoreductases, in samples with complex matrices. The data on the production, properties, and application of complexes of the indicated artificial receptors with the analytes, i.e., organic compounds of different classes, for analytical purposes have been systemized for the first time. Special attention is focused on the discussion of approaches that ensure the specificity of the receptor due to molecular recognition.

Publications devoted to the determination of a number of anions by enzymatic methods are reviewed. The opportunities of utilizing native and immobilized enzymes for the determination of anions in medical, environmental, and food samples are considered.

The incorporation of horseradish peroxidase into polyelectrolyte complexes with chitosans of different molecular weights (MW 5-150 kDa) yielded highly active and stable enzyme preparations. As a result of the selection of optimal conditions for the formation of peroxidase-chitosan complexes, it was found that 0.1% chitosan with a MW of 10 kDa had the strongest activatory effect on peroxidase (activation degree, > 70%) in the reaction of o-dianisidine oxidation by hydrogen peroxide. The complex formed by 0.001% chitosan with a molecular weight of 150 kDa was most stable: when immobilized on foamed polyurethane, it retained at least 50% of the initial activity for 550 days. The highest catalytic activity was exhibited in a 0.05 M phthalate buffer (pH 5.9-6.2) by the complex containing 0.006-0.009% chitosan in the indicator reaction. The activatory effect of the polysaccharide on the enzyme was determined by its influence on the binding and conversion of the reducting substrate peroxidase.

Prospects are outlined for using the following enzymes (native and immobilized on polyurethane foam) in the rapid and highly sensitive determination of cadmium, zinc, and lead ions in plant materials (wild grass, fresh pea, and grape): horseradish peroxidase and alkaline phosphatases isolated from chicken intestine and Greenland seal small intestine. The analytical ranges of the above metals are 1 × 10–3−25, 7 × 10−3−250, and 3 × 10−2−67 mg/kg dry matter, respectively. The enzymatic determination procedures developed are based on the inhibiting effect of metal ions on the catalytic activity of peroxidase in the oxidation of o-dianisidine with hydrogen peroxide and alkaline phosphatases in the hydrolysis of p-nitrophenyl phosphate. The rates of enzymatic reactions were monitored spectrophotometrically or visually. In the analysis of plant extracts, their high acidity was diminished by choosing optimum dilution factors and pH values for test samples and the nature and concentration of a buffer solution. The interference of iron(III) was removed by introducing a 0.1 M tartaric acid solution into the indicator reaction. The accuracy of the results of the enzymatic determination of cadmium, zinc, and lead in plant materials was supported by atomic absorption spectrometry and anodic stripping voltammetry.

The properties of horseradish peroxidase in sodium dodecyl sulfate (DDS) reversed micelles in benzene-pentanol-water solutions are studied. The potential of the analytical application of direct and reversed DDS micelles is demonstrated using newly developed methods for the determination of peroxidase substrates (hydrogen peroxide and cystein), inhibitor (sulfanylamide), and activator (imidazole) via the oxidation of o-dianisidine (o-D) with hydrogen peroxide.

Silica gels modified with different functional groups (amino, epoxy, cycloepoxy, isocyanate, and thiocyanate) were used for the covalent immobilization of horseradish peroxidase (HRP). The catalytic activity and stability of the obtained enzyme preparations were studied using the reaction of o‐dianisidine oxidation with hydrogen peroxide as an indicator. The covalent immobilization of horseradish peroxidase using silica gel modified with thiocyanate groups provided not only the improvement of the enzyme stability, but also the development of the sensitive, rapid, and simple procedures for the determination of fluoride, cyanide, and thiocyanate. Enzymatic determination of inorganic anions is based on their inhibitory effect on the enzyme as the ligands capable to form stable complexes with Fe(III)‐HRP cofactor. The proposed procedures were applied for the determination of F− in mineral and drinking waters; CN− and SCN−—in biological fluids (blood and saliva).

The results of a series of investigations dealing with the development of enzymatic methods for determination of biologically active compounds, viz., inhibitors, activators, and substrates of native and immobilized enzymes of the oxidoreductase (peroxidases, alcohol dehydrogenases) and hydrolase (alkaline and acid phosphatases) classes isolated from diverse sources are summarized. Novel original approaches, proposed by the authors, for improving the sensitivity, selectivity, and rapidity of the methods are discussed. Numerous examples of application of the developed enzymatic procedures for the analysis of a wide range of samples are given.

A test procedure was developed for the determination of 5 × 10−7−1 × 10−3 M copper with the use of the copper-catalyzed reaction of the reduction of molybdophosphoric acid by thiourea on a solid support (paper). The conditions of the indicator reaction and the technique for its conduction were optimized; the pH range in which the acidity of the solution does not affect the time of the reaction was revealed. The calibration plot for the determination of copper was constructed in reaction time-pCu coordinates. The effect of different components on the rate of the indicator reaction was studied. The procedure was approved in the analysis of real and model solutions.

Mercury(II) in the range of 0.1–1 µg L−1 concentrations was found to be a much more efficient inhibitor of native peanut peroxidase (PNP) than of horseradish peroxidase (HRP) in the reaction of o‐dianisidine oxidation with hydrogen peroxide. The possible reason for the different degree of mercury(II) effects on the catalytic activity of both enzymes was studied. It was shown that the different number of glycans in PNP and HRP molecules (three and eight, respectively), or their absence in the molecule of wild‐type recombinant horseradish peroxidase refolded from E. coli inclusion bodies (recHRP), does not play a significant role in the effects caused by mercury(II). The efficient inhibition of PNP by mercury(II) in the absence of any other additives (for example, thiourea) originates from a greater mobility of the distal calcium ion in the enzyme molecule. A model scheme for the interaction of the studied plant peroxidases with mercury(II) was proposed. The PNP‐based enzymatic method for mercury(I...

Peroxidase oxidation of o-dianisidine, 3,3',5,5'-tetramethylbenzidine, and o-phenylenediamine in the presence of sodium dodecyl sulfate (SDS), an anionic surfactant, was spectrophotometrically studied. It was found that 0.1-100 mM SDS concentrations stabilize intermediates formed in the peroxidase oxidation of these substrates. The cause of the stabilization is an electrostatic interaction between positively charged intermediates and negatively charged surfactant.

The effects of magnesium, calcium, and barium ions on the catalytic activity of alkaline phosphatase from the small intestine of the Greenland seal in the reaction of p-nitrophenyl phosphate hydrolysis in the presence of a number of complexones (ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, 1,2-cyclohexanediaminetetraacetic acid, and nitrilotrimethylenephosphonic acid) were studied. As a result, a new approach to the enzymatic determination of the above metals was developed. It consists in the use of the liberative effects of these metals on alkaline phosphatase preinhibited by nitrilotrimethylenephosphonic acid. Sensitive procedures for the enzymatic determination of magnesium, calcium, and barium ions were developed (c min = 14 ng/mL, 24 ng/mL, and 0.8 µg/mL, respectively).

The effect of magnesium ions on the catalytic activity of alkaline phosphatases from three different sources in the reaction of p-nitrophenyl phosphate hydrolysis was studied. It was found that magnesium in concentrations of 0.6 ng/mL-20 µg/mL significantly activated alkaline phosphatase from chicken intestine; in higher concentrations (0.02–0.2 mg/mL), it weakly activated the enzyme from E. coli and had no effect on the catalytic activity of the enzyme from the small intestine of the Greenland seal. The strongest activating effect was observed in a Tris-HCl buffer solution at pH 9.8. The activating effect of magnesium on alkaline phosphatase from chicken intestine was used as the basis for developing a highly sensitive and selective enzymatic procedure for determining magnesium (0.6–6.0 ng/mL; RSD = 4% at cmin; n = 5) by spectrophotometrically monitoring the rate of enzymatic reaction. The developed procedure was applied to the determination of magnesium in urine.

The published data on the nature, strength, and mechanism of metal ion effect on the catalytic activity of alkaline phosphatases and their apoenzymes of different origins are systematized and discussed. Procedures for determining metal ions are described. These procedures are based on the activating, inhibitory, and reactivating effects of metal ions on enzymes and apoenzymes. The approaches to the intentional improvement of the sensitivity and selectivity of determining metal ions are considered. Prospects are outlined for using alkaline phosphatases isolated from different sources in chemical analysis for determining metal ions in different samples.

The effect of zinc(II) and other metal ions on the catalytic activity of native and immobilized alkaline phosphatases isolated from three different sources (Escherichia coli, chicken intestine, and small intestine of Greenland seal) was studied. Zinc(II) inhibits the catalytic activity of all native alkaline phosphatases to different extents. Zinc(II) produces the most significant and selective effect only on the alkaline phosphatase from seal intestine. As for alkaline phosphatases immobilized on polyurethane foam, zinc(II) hardly affects the activity of the enzyme from chicken intestine and inhibits the phosphatases from E. coli and seal intestine in concentrations from 2.5 to 50 μg/mL and 0.1 ng/mL to 50 μg/mL, respectively. With the use of native and immobilized alkaline phosphatase from the small intestine of the seal, selective procedures were developed for the determination of Zn(II) with spectrophotometric and visual control of the reaction rate. The detection limits are 1 μg/mL and 0.1 ng/mL, respectively.

The applicability of the apoenzymes of three alkaline phosphatases of different origin (bacterial from E. coli and animal from chicken intestine or the small intestine of a Greenland seal) to the determination of zinc(II) was studied. The alkaline apophosphatase from seal intestine was found to be promising for this purpose. The preparation conditions of the apoenzyme and the conditions of its reactivation with zinc(II) were optimized. Based on the reactivating effect of zinc(II) on the apoenzyme, which was prepared with the use of EDTA, an enzymatic method was developed for determining zinc(II) (0.01–0.1 μg/mL) with c min = 8 ng/mL. The proposed procedure was applied to the determination of zinc(II) in blood serum.

Methylmercury as well as mercury (II) were found to be effective inhibitors of the catalytic activity of alcohol dehydrogenase from baker’s yeast in the reaction of ethanol oxidation by nicotinamide adenine dinucleotide. It was stated that the methylmercury inhibitory action belonged to the non-competitive type, whereas Hg(II) inhibited the enzyme according to the mixed type. The inversely proportional dependence of the indicator reaction rate on the concentration of methylmercury allowed to develop an enzymatic procedure for its determination with a detection limit of 3 nM. The possibility of methylmercury determination in presence of mercury (II) and mercury (II) determination in presence of methylmercury (concentration ratios CH3Hg+:Hg(II) were 1:1 and 1:10, respectively) was shown. In the first case masking reagents, DEDTC or thiourea, were used to form stable complexes with Hg(II).

Enzymatic methods for the determination of mercury(II) using native and immobilized enzymes from different classes and sources were considered. Enzymatic procedures were compared in sensitivity, selectivity, rapidity, and experimental techniques. The main approaches to controlling the performance characteristics of the enzymatic procedures were discussed. The application of these procedures to the determination of mercury(II) in particular samples (water and soils of different origin and biological fluids) was considered.

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.

The influence of phenol and its derivatives on the kinetics of oxidation of aryldiamines (indicator-substrates) catalyzed by novel plant peroxidase—cationic peanut peroxidase—was studied. The character of influence of phenols on the kinetics of enzymatic oxidation of benzidine, o-dianisidine, and 3,3′,5,5′-tetramethylbenzidine (TMB) with hydrogen peroxide was found to depend on a correlation between redox properties of phenols and the indicator-substrate of peroxidase. Thus, the catalytic activity of peanut peroxidase is inhibited by phenols with redox potentials higher than that of aryldiamines mentioned above, whereas phenols with potentials below those of aryldiamines, play the role of second substrates of the enzyme. The enzymatic procedures for the determination of numerous phenols on the level of their concentrations 0.05–80 μM were developed using the reactions of benzidine, o-dianisidine, and TMB oxidation. Different analytical signals—the indicator reaction rate and the induction period duration—were used for the determination of phenols, belonging to various groups—the inhibitors and second substrates of the enzyme, respectively.

The aims, curricula, and types of professional training of analytical chemists in classical universities are considered. Based on the data of a questionnaire filled at by the members of of analytical chemistry departments, an optimum set of special courses was proposed for the specialty analytical chemistry. An alternative set of special courses corresponding to the applied approach to training analytical chemists is sometimes taught to students of new specialties. A compromise between the two approaches is the introduction of additional educational programs.

The inhibiting effect of heavy metal ions, organic nitrogen-containing heterocyclic compounds, and amino acids on the catalytic activity of yeast alcohol dehydrogenase (ADH) in the reaction of ethanol oxidation by nicotinamide adenine dinucleotide was detected. Sensitive procedures were developed for the determination of the most effective ADH inhibitors [mercury (II), silver(I), zinc(II), copper(II), 1,10-phenanthroline, 2,2′-dipyridyl, 8-hydroxyquinoline, quinoline, 3,4-dimethylimidazole, benzimidazole, 1,2,3-benzotriazole, histidine, tryptophan, proline, and histamine] with cL = 5x 10-10-1 x 10-4M (RSD = 1–12%).

The inhibitory effect of lead(II) towards the activity of alkaline phosphatase immobilized in N -phthalylchitosan on polyurethane foam in p -nitrophenylphosphate hydrolysis has been used for developing a visual test procedure for the determination of 0.05–10 000 ng ml −1 Pb(II). The 3σ detection limit is 0.02 ng ml −1 . Alkaline phosphatase immobilized on polyurethane foam keeps the catalytic activity for at least 1 year. The developed procedure was applied successfully to the determination of lead (14–91 mg kg −1 ) in different types of soils.

Cationic peanut peroxidase was used for the first time for the determination of phenols at a level of 0.5–10μM. The examined phenols were found to be inhibitors or second substrates of peanut peroxidase in the indicator reaction of the oxidation ofo-dianisidine by hydrogen peroxide. The effect of phenols on the rate of the indicator reaction depends on their redox properties. The data on the effects of phenols on the catalytic activities of peroxidases isolated from different sources (peanut, horseradish roots,Medicago sativa alfalfa cells, and the xylotrophic fungusPhellinius igniarius) were compared

A sensitive and selective method for the determination of Zn(II) based on the reactivation of the apoenzymes of alkaline phosphatases from diverse sources: chicken intestine, seal slim intestine and Escherichia coli, has been developed. To obtain the apoenzymes, EDTA was selected as an effective inhibitor of alkaline phosphatases. In the presence of EDTA excess in the solution, the pseudo apoenzymes were obtained. Dialysis of the enzymes against the chelating agent resulted in obtaining inactive zinc-free apo-phosphatases (true apoenzymes). The reactivation of the pseudo- and true apoenzymes of alkaline phosphatases from various sources by zinc(II) was applied for its determination. The proposed procedures are highly sensitive (limit detection of Zn(II) = 0.3-0.4 ng ml−1), selective (no other metals reactivate the apophosphatases from seal slim intestine and Escherichia coli), accurate, simple and rapid. The schemes of the mechanism of the reactivation effects are discussed.

The inhibitory effect of mercury(II) towards the activity of horseradish peroxidase immobilized in chitosan on polyurethane foam in the o -dianisidine oxidation reaction has been used for developing a visual test procedure for the determination of Hg(II) at 1–1000 pg ml −1 . The relative standard deviation at the lower limit of its analytical concentration range is 6% ( n =3). The peroxidase immobilized on polyurethane foam keeps its catalytic activity for more than 1.5 years. The developed procedure was applied successfully for the analysis of different types of soils.

The enzymatic determination of organomercury compounds (methyl-, ethyl-, phenyl-mercury) is based on their effect on the induction period (τind) caused by the introduction of sodium diethyldithiocarbamate to the oxidation of o-dianisidine, o-phenylenediamine and 3, 3′, 5, 5′-tetramethylbenzidine by H2O2 catalysed by native horseradish peroxidase. τind is inversely proportional to organomercury compounds concentration over a range of 0.05–10 μM. The lowest detection limit (Cmin) is 0.03 μM and the standard relative deviation (RSD) is lower than 3%. The proposed method is simple, inexpensive and does not require the preliminary conversion of organomercury compounds to elemental or ionic mercury. The developed procedure is applied successfully to methylmercury determination in water of Kara Sea.

The effect of organomercury compounds (methyl-, ethyl- and phenylmercury) on the activity of immobilized peroxidase was studied. Peroxidase was immobilized in chitosan films in wells on a polystyrene plate and on chromatography paper. The oxidation reactions of o -dianisidine, o -phenylenediamine and 3,3′, 5,5′-tetramethylbenzidine by H 2 O 2 were used as indicators. The rate of all the indicator reactions was monitored visually by measuring the time of appearance of the colour of the oxidation product. The liberating effect of organomercury compounds on peroxidase immobilized on both the above mentioned supports using o -dianisidine oxidation in the presence of the inhibitor phenylthiourea and the effect of organomercury compounds on the duration of an induction period of 3,3′, 5,5′-tetramethylbenzidine oxidation in the presence of diethyldithiocarbamate catalysed by paper-immobilized peroxidase were used for the development of enzymatic test procedures for the determination of organomercury compounds at concentrations of 0.02–1000 μM. The relative standard deviation ( n = 3) at the lower limits of their analytical concentration ranges in the proposed test procedures using o -dianisidine are 18–23% ( n = 3).

A solid-phase fluorescent biosensor for the determination of phenolic compounds (simple substituted phenols and catecholamines) and peroxides has been developed. The biosensor has a simple construction and the analytical signal is measured directly in a biosensitive layer {peroxidase-chitosan} on the sensor surface. This approach allowed analyzing samples with complex matrices (including water-insoluble samples and nontransparent solutions) without their preliminary pretreatment. Two novel fluorescent indicator reactions for the determination of the above-mentioned analytes in wide concentration ranges (from nmol l(-1) to mm l(-1)) which provided an analytical signal registration on a solid phase were proposed. The developed sensor was applied successfully for the analysis of urine, cosmetics, pharmaceuticals preparations, etc.

New test method and test device for the mercury (II) determination at the pg/mL level were developed based on the mercury inhibitory action on horseradish peroxidase immobilized on solid supports – in the cells of the polystyrene plate and on the chromatographic paper. The reactions of o-dianisidine, 3,3′,5,5′-tetramethylbenzidine and o-phenylenediamine oxidation by hydrogen peroxide were used as the indicator reactions. The mercury inhibitory effect increased in the presence of thiourea. Under the elucidated optimal conditions the calibration curves for the mercury determination showed a linear relationship between the peroxidase inhibition degree and the mercury concentration in the range of 0,1–1000 pg/mL. The mercury detection limits were 0,1–10 pg/mL in dependence on the concrete indicator reaction. The analysis completed in 15 min. The proposed test device was applied to the mercury determination in underground waters of Moscow region. The mercury content obtained was coincident with that o...