Microgram determination of vanadium from natural resources

Vanadium has been extracted and determined from a number of natural resources by liquid-liquid extraction technique using N-m-tolyl-o-methoxybenzohydroxamic acid.     

Microgram detection of nitriles using resin beads

Summary Some nitriles (benzonitrile, acetonitrile, propionitrile, butyronitrile, and cyanoacetic acid) can be detected by means of ion exchange resin beads after hydrolysis with dil. H₂SO₄ to produce ammonium ions. The ammonium ions are retained by the resin and then detected by the indophenol blue color using sodium hypochlorite and phenol. The new method is more sensitive and selective than the existing methods.

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Zusammenfassung Einige Nitrile (Benzo-, Aceto-, Propio-, Butyronitril und Cyanessig-säure) lassen sich mit Hilfe von Austauscherharz-Perlen nach Hydrolyse mit verd. Schwefelsäure zur Freisetzung von Ammoniumionen nachweisen. Diese werden an dem Harz festgehalten und dann durch Bildung von Indophenolblau mit Hilfe von Hypochlorit und Phenol nachgewiesen. Diese Methode ist empfindlicher und selektiver als bisher existierende Verfahren.

     

Phase-transfer catalytic determination of phenols as methylated derivatives by gas chromatography with flame ionization and mass-selective detection

A microemulsion electrokinetic chromatographic (MEEKC) method was developed for the separation of six catechins, specific marker phytochemicals of Cistus species. The MEEKC method involved the use of sodium dodecyl sulfate (SDS) as surfactant, heptane as organic solvent and butan-1-ol as co-solvent. In order to have a better stability of the studied catechins, the separation was performed under acidic conditions (pH 2.5 phosphate buffer). The effects of SDS concentration and of the amount of organic solvent and co-solvent on the analyte resolution were evaluated. The optimized conditions (heptane 1.36% (w/v), SDS 2.31% (w/v), butan-1-ol 9.72% (w/v) and 50 mM sodium phosphate buffer (pH 2.5) 86.61% (w/v)) allowed a useful and reproducible separation of the studied analytes to be achieved. These conditions provided a different separation profile compared to that obtained under conventional micellar electrokinetic chromatography (MECK) using SDS. The method was validated and applied to the determination of catechin and gallocatechin in lyophilized extracts of Cistus incanus and Cistus monspeliensis.     

Photometric determination of phenols in essential oils

A photometric procedure is described for determining terpene phenols in essential oils which is based on the formation of colored indophenols with p-quinone chloroimine in an alkaline medium. A comparative evaluation of the results obtained with those of the pharmacopoeial method shows the greater economy, sensitivity, and accuracy of the proposed procedure. Zaporozh'e Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 509–511, July–August, 1988.     

Fast determination of phenols in contaminated soils

An extraction method for the determination of phenols in contaminated soils, based on the application of solid-phase microextraction (SPME) coupled with GC-flame ionization detection analysis, was developed and tested. This method was developed using a natural soil spiked with phenol to a concentration level typical of an acute contamination event that can occur in an industrial site. The effects of the extraction parameters (pH, extraction time and salt concentration) on the extraction efficiency were studied and the method was then applied to determine the pollutant concentration at the beginning and during the biological treatment of a soil, contaminated with phenol and 3-chlorophenol, respectively. The SPME results were validated by comparison with those obtained with an US Environmental Protection Agency certified extraction method. The SPME method was also successfully applied to the determination of the adsorption behavior of 3-chlorophenol on a natural clay soil and was shown to be suitable for different matrices and phenolic compounds. Application of SPME technique results in a sharp reduction of the extraction times with negligible solvent consumption.     

Enzymatic determination of phenols using peanut peroxidase

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.     

Photometric determination of phenols in essential oils

A photometric procedure is described for determining terpene phenols in essential oils which is based on the formation of colored indophenols with p-quinone chloroimine in an alkaline medium. A comparative evaluation of the results obtained with those of the pharmacopoeial method shows the greater economy, sensitivity, and accuracy of the proposed procedure.Zaporozh'e Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 509–511, July–August, 1988.     

Normal-phase high-performance liquid chromatographic determination of phenols

Normal-phase high-performance liquid chromatography has been used for separation of phenol and its monoderivatives. Multi-component mixtures of hexane (non-polar component) with butan-1-ol, chloroform, butyl bromide, butyl chloride or diethyl ether (polar additives) were used as selective eluents. Silica gel "Silasorb 600" with specific surface area of about 600 m(2)/g and average particle size of $ 10 mum was used as the sorbent. Phenol and the o-, m-, p-isomers of cresol were concentrated by extraction with n-butyl acetate from aqueous solutions. A method for determination of microamounts of phenols in aqueous solutions in the presence of 160-fold amounts of aromatic hydrocarbons has been developed.     

HPLC determination of volatile phenols in wines

Summary An alternative to the traditional solvent extraction method used to extract and rapidly quantify ethyl-and vinylphenol and ethyl-and vinylgaiacol from wine is presented. The method is based on retention of volatile phenols on adsorbants. Among the tested resins, the most efficient, AG 2-X8 (anion exchange resin), worked as well with a synthetic solution as with wines. The percolation of clarified wine adjusted to pH 9 on this resin permits, in particular, the elimination of organic acids. Phenols are not eluted after rinsing the column with 1N HCl, but are eluted with methanol after this treatment. Good recovery (91 %) and good repeatability are observed. The eluate is directly analysed by HPLC on an RP18 column after two-fold dilution in water. The four volatile phenols were completely separated and detected by UV at 280 nm with high sensitivity (20–40 ppb). No interference with other compounds were noted in the different wines analysed.     

A direct Capillary Liquid Chromatography with electrochemical detection method for determination of phenols in water samples

A fast and direct method based on the use of Capillary Liquid Chromatography (LC) with electrochemical (EC) detection has been described for phenols pollutants in water samples. Concretely, phenol, o-cresol, 2-chlorophenol and bisphenol A have been selected as target analytes. The combination of Capillary LC with EC detection avoided the necessity of preconcentration steps typically used in environmental analysis. The sample injected volume was 2μL. The achieved detection limits were between 1 and 2μg/L and the linear dynamic range was up to 50μg/L for all studied phenols. The precision and uncertainty were satisfactory. The analysis time per sample was 10min. The proposed procedure has been proved useful for treated waters.     

Electrochemical oxidation and determination of high-molecular-weight sterically hindered phenols

The use of differential pulse voltammetry for the determination of Irganox 1010, a sterically hindered phenol used as an antioxidant, prompted an investigation of the electrochemical behavior of several other commercially available high-molecular-weight hindered phenols used as antioxidants and stabilizers. Although these compounds generally have at least two phenol groups per molecule, their electrochemical behavior is similar to that of simpler hindered phenols such as 2,4,6-tri-t-butylphenol. Detection limits ranging from 1.3 to 8.2 ppm were obtained in a methanol—0.07 M sulfuric acid medium. The oxidation of alkylphenols in neutral or acidic media is accompanied by follow-up chemical reactions, leading to formation of passivating films on the surface of the glassy carbon electrode. In alkaline media, the corresponding phenoxide is oxidized electrochemically to the corresponding stable phenoxy radical and filming can be avoided.     

Milligram determination of aromatic amines and phenols with N-bromosuccinimide

A simple and rapid method has been developed for the determination of milligram amounts of aromatic amines and phenols. An aliquot containing 2-4 mg of sample is dissolved in a mixture of hydrochloric and acetic acids and allowed to react with N-bromo-succinimide, the excess of which is determined iodometrically after the reaction is over. The reaction time varies from 1-10 min and the absolute error generally is negative, ranging from -1 to -4%.     

Sensitive determination of low molecular mass phenols by liquid chromatography with chemiluminescence detection for the determination of phenol and 4-methylphenol in urine

A rapid, reliable method for the routine determination of phenol and 4-methylphenol in urine samples by liquid chromatography with peroxyoxalate chemiluminescence detection was developed. Phenols were first cleaned up by passing the sample through a LiChrolut EN sorbent column and then derivatized straightforwardly with dansyl chloride (15 min at room temperature) thanks to the micellar catalytic effect provided by Triton X-100 micelles. The derivatives were successfully separated in 15 min on a C18 analytical column and determined using an integrated derivatization chemiluminescence detection unit based on the bis(2,4,6-trichlorophenyl) oxalate-hydrogen peroxide system. Linear ranges from 3 to 500 microg L(-1), limits of detection at a signal-to-noise ratio of 3 from 0.3 to 0.5 microg L(-1) and relative standard deviations from 2.8 to 4.7% were obtained. The proposed method was applied to the assay of different human urine samples (healthy, smoker and petrol station worker volunteers) and free and total phenol and 4-methylphenol were determined. The proposed method surpasses other chromatographic alternatives for the determination of these phenols in terms of limit of detection and sample requirements for the analysis.     

Selective detection of carboxylic acids, ureas and phenols and semiquantitative determination of citric acid by capillary solid-state spot-tests

Solid-state spot-tests for the selective detection of carboxylic acids, ureas and phenols have been developed. Mixtures of p-dimethylaminobenzaldehyde with N-methylurea and of p-dimethylaminobenzaldehyde with phthalic acid are used as reagents. Based on these tests a semiquantitative determination of citric acid is also developed. These tests utilize three properties of the coloured boundary: colour, length and direction of movement. Our work on capillary solid-state spot-tests,(1) has now been extended to some further organic compounds.     

Synthesis of nitro- and aminoindoles

Optimal conditions are proposed for the direct nitration of 2,3-dimethylindoles containing methyl and methoxy groups in the benzene ring. In contrast to 5- and 6-methylindoles and 5- and 6-methoxyindoles, nitration of 7-methyl-and 7-methoxy-2,3-dimethylindoles proceeds differently under the same conditions. A series of previously unreported aminoindoles was obtained by reduction of the nitroindoles.Mordova State Pedagogical Institute, 430007 Saransk, Russia; e-mail:mgpi@si.moris.ru and M. V. Lomonosov State University, 119899 Moscow, Russia, e-mail:yumar@org.chem.msu.su. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1630–1636, December, 1999.     

Kinetic determination of phenols by a fixed-time method

The fixed-time kinetic method is used for the determination of 15 phenols in methanol and acetic acid by measurement of the yellow products from the oxidation of the phenols with sodium metaperiodate. An increase in acid and metaperiodate concentrations enhances the rate of reaction, whereas the use of 2-propanol as the solvent decreases it.     

Synthesis of nitro- and aminoalkylphosphonates

Conclusions Some new O, O-dialkyl nitroalkylphosphonates were synthesized by the addition of dialkyl phosphites and thiophosphites to nitroolefins. The corresponding aminophosphonates were obtained from them by reduction. The hydrolysis of the latter gave the corresponding aminoalkylphosphonic acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1164–1168, May, 1972.