Determination of abamectin and doramectin in sheep faeces using HPLC with fluorescence detection

An analytical procedure for the determination of abamectin and/or doramectin in sheep faeces has been developed. Avermectins were extracted from sheep faeces with acetonitrile, clean-up using solid phase extraction (SPE) and analysed by high performance liquid chromatography (HPLC) with fl uorescence detection after derivatization with N-methylimidazole.The method has a low detection limit (1.0 ng/g of moist sheep faeces), low quanti fi cation limit (2.5 ng/g of moist sheep faeces), good recovery in the range 66.4-80.8% for abamectin and 67.7-85.5% for doramectin as well as good repeatability (>85%). The method is applicable to the study of the time pro fi le of excretion in sheep faeces and also for ecotoxicological studies of both avermectins.     

Role of hydrogen bonding in the oxidation of thianthrene 5-oxide with peroxy acids.

The oxidation of thianthrene 5-oxide, i.e., a mechanistic probe for the assessment of the electronic character of various oxidants, with peroxybenzoic acids in various oxygen bases as solvents was investigated. The nucleophilicity (X(SO)) of peroxy acids was increasing with increasing basicity of the oxygen base. A good linear correlation was observed by plotting X(SO) values vs either the Kamlet-Taft beta values or the OOH (1)H NMR chemical shifts of m-chloroperoxybenzoic acid (m-CPBA) in solvents of various basicity. These observations, together with the results of IR and (1)H NMR spectroscopic studies of peroxybenzoic acids, and DFT (B3LYP/6-311++G) studies of the intramolecular hydrogen bonding in peroxyformic, peroxyacetic, and m-CPBA, as well as the intermolecular hydrogen bonding in the complexes of the these peroxy acids with dimethyl ether as a model oxygen base, support the involvement of the peroxy acid-oxygen base complexes in the transition states of these reactions. The increased nucleophilicity (X(SO)) of peroxy acids in basic solvents is most likely due to the increased negative charge on the terminal "electrophilic" peroxycarboxylic oxygen atom (OH), and/or the increased LUMO and HOMO energies of the peroxy acid in the complexes, as compared to those parameters in the intramolecularly hydrogen-bonded form of peroxy acids, believed to be operative in inert solvents.     

Effect of mobile phase nature on the selectivity of separation of 5,7-dinitrobenzofurazan derivatives of amino compounds by reversed-phase HPLC

Selectivity coefficients of a series of 5,7-dinitrobenzofurazan derivatives of amino compounds in the separation by reversed-phase HPLC have been calculated. Influence of the character and concentration of organic modifier and pH of the buffer solution in the mobile phase on the selectivity of separation of the studied compounds has been determined.     

Sorption-chromatographic determination of hydrazine and its substituted derivatives in air

Working conditions were found for the chemisorption preconcentration of hydrazine, phenylhydrazine, and 1,1-dimethylhydrazine from air with tubes containing silica gel with immobilized 4-chloro-5,7-dinitrobenzofurazan and the subsequent determination by high-performance liquid chromatography with diode array detection. A recovery of 98% (hydrazine), 90% (phenylhydrazine), and 97% (1,1-dimethylhydrazine) is attained at a thickness of the sorbent layer of 2 cm, an aspiration rate of 0.2–0.8 L/min, and a volume of aspirated air of 10 L. Silica gel with a particle size of 0.1–0.3 mm impregnated with 4-chloro-5,7-dinitrobenzofurazan (2 wt %) was used as the sorbent. The detection limits of compounds without regard for preconcentration after their desorption are 0.01 (hydrazine), 0.017 (1,1-dimethylhydrazine), and 0.015 mg/m³ (phenylhydrazine).     

Selective spectrophotometric determination of proline and tryptophan as 4,6-dinitrobenzofuroxan derivatives in the presence of other Amino Acids

Working conditions of the spectrophotometric determination of proline and tryptophan as 4,6-dinitrobenzofuroxan derivatives in the presence of different amino acids were found. Optimal conditions of the detection of proline and tryptophan are 510–530 nm and 540–560 nm, respectively, after the reaction at pH 6.7–7.5. The detection limit is 1 |Xg/tnL for tryptophan and 0.7 (Ag/mL for proline; the analytical range is 1–40∥lmL. It was demonstrated that proline and tryptophan can be determined by spectrophotometry in fermentation solutions in the biosynthesis of these amino acids.     

Spectrophotometric and chromatographic determination of sulfanilamides in biological fluids and pharmaceuticals

The conditions for the determination of norsulfazol (I), sulfadimezine (II), ethazole (III), sulfamethoxypyridazine (IV), sulfadimethoxine (V), sodium sulfacyl (VI), sulfalene (VII), sulgin (VIII), and bucarban (IX) as their derivatives of 4,6-dinitrobenzofuroxan using spectrophotometry and thin-layer chromatography were selected. The best results were obtained at 490–500 nm using polar solvents and their aqueous mixtures of pH 6.68 as analytical media. The analytical range for sulfanilamides was 0.5–6.0 Μg/mL. The limits of detection (Μg/mL) were 0.24 for 1,0.28 for II, 0.43 for III, 0.18 for IV, 0.25 for V, 0.54 for VI, 0.54 for VII, 0.17 for VII, and 0.31 for IX. Sulfanilamides were determined in Pharmaceuticals (tablets, ointments, and drops) and biological fluids (protein hydrolyzates, urine, blood serum, and whole blood). A simple rapid method for the determination of the phenotype of biotransformation by the type of acetylation was developed based on the studies of the kinetics of the excretion of II from the human body with urine.     

Phase transitions in the adsorbed molecular chains

Rotational excitations of molecular adsorbed layers are studied theoretically. Nonlinear dynamical equations are obtained with accounting of quadrupolar interactions between molecules and freezing of translational degrees of freedom. The equilibrium positions of the molecules are found to be experimentally observed structures with alternating rotational ordering of planar rotors along the direction to the nearest neighbor (for linear or square structures) under low temperature. Dynamical analysis gives an integral of motion (energy) of the chain that in the long-wave limit leads consequently to the existence of four phases. The first one corresponds to oscillations near equilibrium ordered states. The second phase corresponds to low-energy rotational excitations along ‘valleys’ (easy directions in the effective potential) that do not destroy strong correlations between molecules while structural data can show rotational disorder (melting). The third phase corresponds to an energy that is enough to travel between ‘valleys’; only some ‘islands’ in the angle space are forbidden. Complete destruction of correlation when the energy is over the peaks of the effective potential corresponds to the fourth phase. Therefore rotational melting is a complex phenomenon that has several stages. Presented at the 2nd International Conference “Physics of Liquid Matter: Modern Problems” (September 2003, Kyiv, Ukraine).     

A passive chemical dosimeter for assessing long-term exposure in air containing aniline and aniline derivatives

A passive chemical dosimeter for assessing long-term exposure to toxic substances (aniline and its derivatives) in the atmosphere of inhabitable premises was described. The compounds to be determined were accumulated on an absorption filter due to a chemical reaction with a selective agent upon the many-hour exposure of the device. Analytical performance of chemical dosimeters (diffusion coefficients, chemisorption pre-concentration rate, and detection limits) was evaluated. The concentrations of aniline, p-chloroaniline, 3,4-dichloroaniline, and o-toluidine in the air of chemical laboratories and smoking rooms were determined.     

Evidence for HOOO radicals in the formation of alkyl hydrotrioxides (ROOOH) and hydrogen trioxide (HOOOH) in the ozonation of C-H bonds in hydrocarbons.

Low-temperature ozonation of cumene (1a) in acetone, methyl acetate, and tert-butyl methyl ether at -70 degrees C produced the corresponding hydrotrioxide, C(6)H(5)C(CH(3))(2)OOOH (2a), along with hydrogen trioxide, HOOOH. Ozonation of triphenylmethane (1b), however, produced only triphenylmethyl hydrotrioxide, (C(6)H(5))(3)COOOH (2b). These observations, together with the previously reported experimental evidence, seem to support the "radical" mechanism for the first step of the ozonation of the C-H bonds in hydrocarbons, i.e., the formation of the caged radical pair (R(**)OOOH), which allows both (a) collapse of the radical pair to ROOOH and (b) the abstraction of the hydrogen atom from alkyl radical R(*) by HOOO(*) to form HOOOH. The B3LYP/6-311++G(d,p) (ZPE) calculations revealed that HOOO radicals are considerably stabilized by forming intermolecularly hydrogen-bonded complexes with acetone (BE = 8.55 kcal/mol) and dimethyl ether (7.04 kcal/mol). This type of interaction appears to be crucial for the relatively fast reactions (and the formation of the polyoxides in relatively high yields) in these solvents, as compared to the ozonations run in nonbasic solvents. However, HOOO radicals appear to be not stable enough to abstract hydrogen atoms outside the solvent cage, as indicated by the absence of HOOOH among the products in the ozonolysis of triphenylmethane. The decomposition of alkyl hydrotrioxides 2a and 2b involves a homolytic cleavage of the RO-OOH bond with subsequent "in cage" reactions of the corresponding radicals, while the decomposition of HOOOH is most likely predominantly a "pericyclic" process involving one or more molecules of water acting as a bifunctional catalyst to produce water and singlet oxygen (Delta(1)O(2)).     

High-performance liquid chromatography of 5,7-dinitrobenzofurazan and nitrobenzodifurazan derivatives of aromatic amines

The retention times of 5,7-dinitrobenzofurazan and nitrobenzodifurazan derivatives of aromatic amines in reversed-phase high-performance liquid chromatography on a column filled with Hypersil ODS correlate with the acidity constants of these derivatives in dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) and with the σ constants of substituents in the aromatic nucleus. Procedures were developed for the determination of aniline, N-methylaniline, N,N-dimethylaniline, and N-ethylaniline as their 5,7-dinitrobenzofurazan and nitrobenzodifurazan derivatives with detection limits of 70 μg/mL. The procedures can be used for the analysis of reaction mixtures in the synthesis of these substituted amines.