I. G. Zenkevich

Volatile organic compounds in the atmosphere of forests

Abstract The procedure of sampling and gas chromatographic-mass spectrometric analysis of air containing volatile emissions from living plants has been elaborated. The qualitative composition of volatile organic compounds (VOC) produced by 22 species of plants which are characteristic for Northern hemisphere forests has been studied. The emission rate of isoprene and terpenes for some of them has been determined. Terpene concentrations in coniferous forests of different regions of the U.S.S.R. have been also determined. The list of compounds identified includes more than 70 substances of different classes. Total terpene concentrations in the coniferous forests air usually vary from 3.5 to 35 μg −3 . Strong influence of meteorological conditions on the emission rate and terpene concentrations in the air under the forest canopy has been noted.

Gas chromatographic-mass spectrometric determination of volatile organic compounds in an urban atmosphere

Polysorbimide and carbochrome, new sorbents with high temperature stability, have been used to concentrate trace amounts of atmospheric pollutants, and 136 C1-C13 organic compounds, including 126 hydrocarbons, 6 oxygen derivatives and 3 chlorides, were identified in air samples collected in the streets of Leningrad. One of the major features of the composition of the organic constituents of the urban air sampled is the presence of a number of CnH2n hydrocarbons (mainly olefins), and also CnH2n-2 and CnH2n-4 unsaturated hydrocarbons (including alpha-pinene and camphene). A comparison of the results with those of similar studies carried out on air samples from Zürich, Houston and Paris is of considerable interest in connection with the possible effect of geographical factors on the composition and lifetime of organic pollutants in the atmosphere.

A new version of an additive scheme for the prediction of gas chromatographic retention indices of the 211 structural isomers of 4-nonylphenol.

Control of environmental pollution by 4-nonylphenols (4-NP) and effective risk assessment concerning these xenoestrogens requires the identification of the individual isomers contained in the technical mixtures of 4-NP. A new approach is presented here which supports the identification of these compounds by a combination of experimentally determined gas chromatographic retention indices (I) of reference 4-NP isomers and calculated I-values. In addition to experimental indices, the I-prediction algorithm includes a new version of an additive scheme. The I-values of all structural 4-NP isomers are calculated on the basis of experimentally determined indices of a few available 4-NP isomers and the known retention indices of 75 iso-decanes. A mean deviation of +/-11 index units between predicted and experimental I-values demonstrates the feasibility of the new approach. The predicted I-values provide information on the structure of 4-nonylphenol isomers in the technical mixture which has not been considered before. Furthermore, a novel line-coding system is proposed to describe the structure of isomeric 4-NPs and to initiate a current database for the endocrine-disrupting 4-nonylphenols.

System of retention indices for a linear temperature programming regime

Abstract The possibilities and advantages of the recently proposed system of linear—logarithmic retention indices for chromatography with linear temperature programming are discussed. In contrast to previously known systems of retention indices, an additional parameter is introduced in which the experimental conditions are taken into account and which is determined from the retention times of reference compounds. The linear—logarithmic retention indices are characterized by high reproducibility under any conditions of linear temperature programming, irrespective of the choice of reference compounds, and can be directly compared with Kovats retention indices.

Methods and results of gas chromatographic-mass spectrometric determination of volatile organic substances in an urban atmosphere

Abstract The method and results of the quantitative gas chromatographic determination of volatile organic substances in an urban atmosphere are presented. The concentration of organic substances was determined by using a mixed adsorber consisting of graphitized thermal carbon black and activated charcoal modified by pyrocarbon. Average, maximum and minimum concentrations of constant organic components in the atmosphere of Leningrad as a typical large industrial city are reported.

Prediction of retention indices for identification of fatty acid methyl esters

Quantitative structure-retention relationships have been developed to predict retention indices of fatty acid methyl esters on standard non-polar polydimethylsiloxane stationary phases. Branched, saturated and unsaturated compounds were included. All retention indices have been evaluated by statistical processing of experimentally measured and literature data in accordance with the concept of interlaboratory data randomization. Multiple linear regression (MLR) has been carried out to find relationships between selected properties and retention indices. Models have been built in two different ways (i) the same degrees of freedom for all models have been fixed and the variable selection ability has been compared; (ii) variable selection methods have been used in their best performance. The five selection methods were: pair-wise correlation, forward selection, partial least squares projection of latent structures, modified best subset selection and the Lasso method. The stability and the validity of models have been tested by internal and external validation. The error of predicted retention indices is close to the error of interlaboratory reproducibility of retention indices. The most relevant variables in description of retention indices were molecular mass, number of double bonds and number of rotatable bonds complemented with topological descriptors. Predictive models have been built for 130 fatty acid methyl esters for identification purposes. Moreover, prediction of unknown retention indices for 37 fatty acid methyl esters has also been carried out.

A comparison of the external standard and standard addition methods for the quantitative chromatographic determination of pesticide concentrations in plant samples

Model samples containing known amounts of pesticides in various plant materials were analyzed, and the accuracies of the external standard and standard addition methods were compared based on a criterion such as the relative analyte concentration. It was found that traditionally recommended procedures for the solvent extraction of pesticides from samples of this kind in combination with quantitative analysis by the external standard method determine only 10–70% of the true concentrations of analytes. This is most likely due to analyte adsorption on matrices and/or incomplete extraction. In almost all cases, the use of the standard addition method compensates pesticide losses at the stages of sample preparation and thereby considerably decreases the systematic error of determination. The extrapolation of analyte concentration to the zero amount of the added reference sample was proposed to additionally control the accuracy of results obtained by the standard addition method. Moreover, it was found that solid-phase extraction as the second stage of sample preparation has no considerable advantages over back solvent extraction in terms of the above criterion. This is because the main analyte losses were observed at the first stage of extraction from test samples.

Determination of dissociation constants of species oxidizable in aqueous solution by air oxygen on an example of quercetin

The comparison of literature data on the dissociation constant of one of the most abundant natural flavonoids, e.g., quercetin, demonstrates their irreproducibility. The reason for this likely corresponds to the easiness of its oxidation by air oxygen during the titration process. To eliminate such problems, a modified version of potentiometric titration was proposed with bubbling a weak flow of an inert gas (nitrogen) through the solution to be titrated in the presence of minimal amounts of a nonionic surfactant. By virtue of the technique proposed, the values of pKa for quercetin were measured to be 6.62 ± 0.04 and 9.7 ± 0.3. The first one corresponds to the hydroxyl group in the γ-pyrone fragment of the molecule, while another agrees with the typical values of pKa for phenols.

Essential Oils of Salvia sclarea L. Produced from Plants Grown in Southern Uzbekistan

ABSTRACT The composition of the essential oils obtained from different parts of both wild and cultivated forms of Salvia sclarea L. were investigated by both GC and GC/MS. The principal components of the oils were linalool (22–32%) and linalyl acetate (25–51%). It was found that the oil composition was not influenced by the part of the plant from which oil was obtained, except for the leaves. Oil composition was not influenced by plant parts (except for the leaves), state of plant maturity, location of cultivation site, whether the plant was wild or cultivated, year of harvest, color of bracts or cultivation conditions.

Hydrolysis of organonitriles and carboxamides in platinum(IV) complexes. X-ray structure determination of the crystalline clathrate {(C2H5)}4N [Pt(NH3)Cl5]· NH4Cl

Abstract Complexes [PtL(dmso)Cl 4 ] (L = MeCN, PhCN, MeCONH 2 , PhCONH 2 ) are easily subject to hydrolysis at 20 °C and form a mixture of the ammine complexes Pt(IV) and corresponding carbonic acids. As a result of hydrolysis of [Pt(MeCN)(dmso)- Cl 4 ] followed by addition of (Et 4 N)Cl to the mixture, the crystalline clathrate (Et 4 N)[Pt(NH 3 )Cl 5 ]· 1 6 NH 4 Cl was obtained. The compound has the following X-ray structure: it crystallizes in the rhombohedric space group R 3 ; unit cell parameters: a = 25.050(3), c = 13.846(2) A; Z = 18, ϱ calc = 2.09 g cm −3 . Bond lengths in the slightly distorted octahedric anion [Pt(NH 3 )Cl 5 ] − are: Pt-N 2.065(10); Pt-Cl cis 2.331(3), 2.314(3), 2.327(3), 2.316(3); Pt-Cl trans 2.313(3)A.