In extraction systems hexane–water, hexane–aqueous solutions of inorganic salts (sodium chloride, dipotassium phosphate and potassium carbonate), chloroform–water using the method of gas chromatography–mass spectrometry, the distribution constants of psychotropic substances, limited to movement through the customs border of the Republic of Belarus – alprazolam, lorazepam, temazepam, and as well as clozapine, a medicinal product permitted for movement, were determined. The greatest dynamics of the growth of the distribution constant versus salt concentration was observed in alprazolam. It was found that replacing hexane with chloroform leads to increasing the distribution constants and the quantitative extraction of all substances. However, for the selective extraction of substances from various objects and the simultaneous removal of matrix components, it is necessary to use the systems as hexane–aqueous solutions of salts or hexane–water. Based on the obtained values of the distribution constants of substances, extraction-chromatographic technique for the determination of organic non­electrolytes (benzodiazepines) in various objects is proposed. Metrological characteristics of the techniques are: relative standard deviation does not exceed 2 %, the range of determined concentrations in solutions is 0,05– 1,00 g/dm3.

A critical review of the methods for producing pyrolysis waste oils was carried out, the possibilities and limitations of each approach were discussed. Liquid pyrolysis products (pyrolysis oils) are promising source of valuable chemical compounds, and can be also used as a fuel. A reliable analysis of pyrolysis oils is necessary to study their component composition, basic characteristics and to select the most suitable methods for the extraction of the necessary compounds. It is known that the results of GC-MS analysis of liquid pyrolysis products are usually ambiguous: there are problems of peaks overlapping and incorrect interpretation of the data, due to the complexity of the matrix and the multicomponent composition of the object. The paper presents data on the chemical composition of pyrolysis oils obtained by elemental analysis, IR spectroscopy, NMR spectrometry, GC-MS, GC-GC/MS. Based on the presented results, pyrolysis oil usually contains aromatic compounds, water-soluble substances and hydrocarbons. It was found out that there are conflicting data on the chemical composition of the pyrolysis oils of waste tires in the scientific literature. It is proposed to carry out sequential extraction sample preparation of pyrolysis mixtures to increase the reliability and accuracy of the componential and quantitative composition of the GC-MS method. Obviously, a reliable analysis of complex pyrolysis mixtures without preliminary targeted sample preparation seems unlikely.

A standardized procedure is developed for the determination of chloramphenicol in food products of animal origin of different groups using HPLC with tandem mass spectrometric detection with a limit of detection of 0.2 µg/kg. The extraction of chloramphenicol from aqueous solutions with organic solvents was studied. Optimized procedures for the extraction of chloramphenicol, purification of the extracts, and preconcentration of the analyte and the use of the deuterated form of chloramphenicol ensure quantitative determination using an external calibration method with an internal standard with the maximum expanded uncertainty of the results 18.4%.

Using gas chromatography methods with the quadrupole mass spectrometric detector and flame ionization detector, as well as high-performance liquid chromatography with the diode-matrix detector, the distribution constants of codeine, phenobarbital, modafinil, adrafinil, pseudoephedrine for hexane-water, hexane-water systems of inorganic salt solutions (sodium chloride, dipotassium phosphate, potassium carbonate and ammonium sulfate), chloroform-water, chloroform-aqueous solutions of inorganic salts (sodium chloride, dipotassium phosphate, potassium carbonate and ammonium sulfate) were determined. The principal possibility of quantitative extraction of all the investigated substances from the aqueous matrices by salting out was shown. The patterns of salting out of the studied substances from the aqueous solutions were established. In particular, the salting out ability of salts increased sharply with the increasing charge of the salt anion. A significant effect on the salting out effect was exerted by the nature of the extracted compound. It has been shown that the following compounds could be quantitatively recovered in the hexane: codeine, modafinil, and afrafinil. Due to their high hydrophilicity, phenobarbital and pseudoephedrine were not quantitatively extracted with the hexane even at the salt concentration close to the saturation. For the extraction of phenobarbital and pseudoephedrine, the more active but less selective chloroform was used. Based on the obtained values of the distribution constants of the substances and their acid-base properties, the extraction methods for the sample preparation of the various objects were proposed with determining the studied substances in them using salting out. The methodology for the determination of pseudoephedrine and codeine in drugs was tested. It was based on the preliminary removal of the matrix components by chloroform from the aqueous acidic solution and subsequent alkalization, salting out, and extraction with chloroform. The characteristics of the methods were as follows: detection limit for pseudoephedrine - 0.09 g/dm 3 and for codeine - 0.07 g/dm 3 ; standard deviation did not exceed 4% for both substances, range of determined concentrations for all-ephedrine was 0.09 – 3.00 g/dm 3 , and for codeine - 0.07 - 4.00 g/dm 3 respectively. Key words : salting out, chromatography, increment of methylene group, solution structure, Sechenov constant (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.4.004 S.M. Leshchev 1 , O.N. Mikhniuk 2 , K.D. Kryzhny 2 , M.F. Zayats 1 1 Belarusian State University, ul. Leningradskaya, 14, Minsk, 220050, Republic of Belarus 2 State institute of advanced training and retraining of customs authorities of the Republic of Belarus, ul. Mogilevskaya, 45/4, Minsk, 220007, Republic of Belarus

At a temperature of 20 ± 1 °C, the distribution of model substances of various classes of organic non-electrolytes in n-hexane – aqueous solutions of dipotassium phosphate and potassium acetate was studied. The increments of the methylene and functional groups of organic non-electrolytes are calculated. It has been shown that in case of dipotassium phosphate, the nature of the salting out effect is enhancing the structure of the salt solution and the growth of the methylene group increment. For potassium acetate, the increment of the methylene group slightly increases with increasing salt concentration, and for most functional groups it increases significantly. An explanation of the dependences of the increment values on the nature and composition of the salt solution is given.

The distribution of ethanol and butanol between n-hexane and aqueous solutions of ammonium sulfate at 20 ± 1°C was studied over an ideal concentration region of the substances in the organic phase. The distribution constants of the substances and the increments of the methylene and hydroxyl groups of the alcohols in the logarithm of the distribution constant were calculated. It was found that an increase in the salt concentration in the aqueous phase resulted in a considerable increase in the increment of the methylene group and significantly improved the alcohol separation efficiency. The dependence of the distribution coefficients of ethanol and butanol on the concentration of ethanol in the aqueous phase was studied. A dramatic decrease in the increment of the methylene group was found as the ethanol concentration in the salt phase was increased above 4.5 vol %. A procedure was developed for extraction sample preparation for the subsequent determination of the characteristic components of cognac products and for the authentication of these products by gas chromatography. The essence of this procedure consists in the hexane extraction of butanol and other hydrophobic substances from cognac product samples prediluted with an aqueous solution of ammonium sulfate. In this case, the major portion of ethanol, as well as hydrophilic and thermally unstable impurities, which complicate analysis with direct sample injection, remained in the salt solution. The procedure was tested with 16 samples of cognac and cognac spirits from Georgia, including both authentic and adulterated products.

For cyclopentane used as a model hydrocarbon, solubility in water and aqueous solutions of various salts (chlorides, bromides, iodides, rhodanides, alkali metal acetates and sulfates, and calcium and zinc chlorides) at 20 +/- 1degreesC has been determined. Variations of the increment of the methylene group (DeltaI(CH2)), induced by salt additions to water, are calculated. When the salt is added to the solution, the increment I-CH2 increases drastically irrespective of the nature of the ions, thus stabilizing the structure of the solution. The increase, however, depends significantly on the nature of the salt, which is explained by different degrees of structuring of the aqueous solution caused by the ions of the salts.

A method was proposed for estimating Gibbs energies of solvation of aromatic hydrocarbons in sol vents of different nature and polarity. It was established that Gibbs energies of solvation of hydrocarbons in n-octane are linear with their molar volume; this provides a means of calculating the Gibbs energy of the nonspecific solvation in n-octane for an aromatic hydrocarbon with an arbitrary molecular weigh and an arbitrary structure. Gibbs energies of solvation of hydrocarbons in solvents of different nature were calculated from Gibbs energies of solvation in octane.

The partition,of benzene and biphenyl in organic solvent-water systems was studied at a temperature of 20 +/- 1 degreesC. The solubility of hexamethylbenzene, p-terphenyl, and 1,3,5-triphenylbenzene in solvents of various natures and polarities (hydrocarbons and their halogenated derivatives, alcohols, ketones, ethers, and esters) was determined at this temperature. The Gibbs free energies of the transfer of aromatic hydrocarbons from the n-octane to the solvents were calculated. The additivity of the transfer free energies was found, and a correlation equation for calculating of the transfer free energies for aromatic hydrocarbons of different structures and molecular weights was proposed. It was found that halogenated hydrocarbons, benzene, ketones, and esters have the highest solvating power with respect to aromatic hydrocarbons, and alcohols, aliphatic hydrocarbons, and ethers have the lowest solvating power.

The solubilities of anthracene, tetracene, 1,2-benzanthracene, chrysene, pyrene, perylene, α,α'-dinaphtyl, rubrene, and decacyclene in solvents of different nature and polarity (hydrocarbons and halogenated hydrocarbons, alcohols, ketones, ethers, and esters) were determined at 20±1°C. The distribution of benzene and naphthalene in the organic solvent-water system was studied. The Gibbs energy of transfer of aromatic hydrocarbons from n -octane to organic solvents was calculated.

Some regularities of the energetics of structure formation in mixtures of polar organic solvents not forming layered structures with liquid hydrocarbons and in mixtures of inert and low-polar diluents at 20\( \pm 1{\kern 1pt} {\kern 1pt} ^\circ C\) were established. In most cases, the deviation of the methylene group increments from additivity, defining the energy stability of a liquid structure, was distinctly negative. In particular, the increment decreases dramatically from individual higher alcohols to mixtures of propanol and n-octane which model the former in the concentration of functional groups per unit volume, and the structure of mixture is weakened. Solvents of close polarity, in turn, form mixtures whose methylene group increments are well approximated by the additivity law.

The solubility of n-tetracosane and n-dotriacontane as model paraffin hydrocarbons in solvents of different natures and polarities was studied at various temperatures. The feasibility of extractive fractionation of mixtures of higher paraffins and ceresins according to their molecular mass was revealed, as their solubility drastically decreases with the increasing paraffin or ceresin molecular mass and increasing solvent polarity. Procedures for the fractionation of laboratory paraffin wax and ceresin based on the extraction of hydrocarbons of a lower molecular mass with hot isopropyl alcohol were developed. Fractions of higher paraffins and ceresins were isolated and characterized.

The magnitude of the solvophobic effect for more than 160 solvents of different natures and polarities (hydrocarbons, their derivatives, alcohols, ketones, ethers, amines, nitriles, carboxylic and inorganic acids, polyfunctional compounds, and some inorganic liquids) was characterized by the Gibbs energy of transfer of the methylene group from the solvent to n-octane, a quantity that was measured experimentally. It was revealed that these values vary from +0.04 to -0.82 kcal/mol. This was explained by the different propensities of the solvents to molecular self-association with the formation of a spatial structure and by the differences in the efficiency of their dispersion interactions with the methylene group. The influence of the solvophobic effect on the extraction and solubility polynuclear aromatic hydrocarbons (PAHs), an important class of hydrophobic organic compounds, was assessed. Some aspects of their extraction and solubility in various solvents that are difficult to explain were interpreted. The influence of the solvophobic effect on the extraction of PAHs from aqueous solutions was shown to be a key factor.

The solubility of various liquids in perfluorodecalin is determined at 20 +/- 1 degreesC. With the extraction system n-hexadecane-pernuorodecalin the distribution of various classes of nitrogen-, oxygen-, halogen-, and sulfur-containing organic nonelectrolytes, and unsaturated and aromatic hydrocarbons is studied. The increments of the methylene and various functional groups of organic nonelectrolytes in log K-D are estimated.

The distribution of condensed aromatic hydrocarbons containing 2-5 "joined" aromatic rings per molecule between octane and polar organic solvents of different nature has been studied at a temperature of 20 degrees C + 1 deg. The dependences of the distribution constants of condensed aromatic hydrocarbons on the number of aromatic rings per molecule, the type of joining and the nature of the polar organic solvent have been established. The solvent groups characterized by different orders of extractability of condensed aromatic hydrocarbons have been determined. It has been shown that the extraction of substituted condensed aromatic hydrocarbons, in contrast to that of sunstituted benzenes, cannot be described from positions of the principle of additivity of the free energy of distribution. The basic possibility of extraction separation of condensed aromatic hydrocarbons and their isolation from hydrocarbon feedstock and surrounding media has been demonstrated. (C) 1998 Elsevier Science Ltd. All rights reserved.

A study has been made of the distribution of benzene, hexamethylbenzene, diphenyl, fluorene, p-terphenyl and 2,4,6-triphenylbenzene between n-octane and 12 polar solvents of different nature at a temperature of 20 degrees C +/- 1 deg. The laws governing change in the distribution constants of substances as a function of the structure of their molecules and the nature of the polar solvent have been established. With the use of data on the extraction of benzene and hexamethylbenzene, the question of the relationship of the contributions of the solvation of protons of the benzene ring and its pi-electron system to the total energy of solvation by the polar phase is discussed at a qualitative level. The most effective extractants for polycyclic aromatic hydrocarbons are proposed. (C) 1997 Elsevier Science Ltd. All rights reserved.

A study has been made of the distribution of diphenylsulphide, diphenylsulphoxide, thiophene and dibenzothiophene in extraction systems consisting of octane and polar organic solvents and octane and water-organic mixtures. The relationships governing the distribution of diphenylsulphide and diphenylsulphoxide are explained on the basis of the principle of additivity of the free energy of distribution. It is shown that the replacement of aliphatic substituents with aromatic substituents reduces the capacity of the sulphide group and, especially, the sulphoxide group to be solvated by the polar phase, The similarity in the nature of change in the distribution constants of thiophene and dibenzothiophene on the one hand and aromatic hydrocarbons on the other as a function of the nature and composition of the polar phase has been established. (C) 1996 Elsevier Science Ltd.