The Methodology of Application of Liquid-Liquid Extraction for Sample Preparation of Water, Soil and Various Kinds of Agricultural and Food Products for their Ecological Safety Control by Chromatographic Methods

Mikhail Zayats, The Laboratory of Dynamics of Pesticides, RUE “Institute of Plant Protection”, a/c Priluki, Minsk distr., Republic of Belarus
Sergey Leschev, Analytical Chemistry Department, Belarusian State University, Faculty Of Chemistry, Minsk, Republic Of Belarus
Marina Zayats, The Laboratory Of Dynamics Of Pesticides, Rue “institute Of Plant Protection”, A/c Priluki, Minsk Distr., Republic Of Belarus

Issues of quality control and safety of agricultural products and of safety of environmental objects based on content of the characteristic and alien components are extremely relevant. The success of chromatographic method, which is most commonly used for these purposes, is stipulated mainly by preliminary sample preparation.

Solvent extraction is one of the most simple and effective methods of sample preparation, providing the separation of the impurities (analytes) and matrix components. However, so far no suitable algorithm is formulated for choosing the suitable extraction system and the conditions of the extraction process.

The methodology for the selection of the optimal extraction system is proposed. It is based on a systematic study of molecular and dissociation extraction of ~2000 model, matrix and impurity compounds in ~200 extraction systems, including organic solvent – water and salt solutions, hydrocarbon – polar organic solvents and aqueous-organic mixtures. The obtained data is generalized on the basis of the principle of additivity of Gibbs energy of distribution, also known as the method of group increments. Group increments characterize properties of extraction systems with respect to substances containing these groups. The experimental constants and constants calculated using increments in most cases are in good agreement. The dependences of group increments on the nature and composition of the phases of extraction systems are used for the estimation of distribution constants of substances and selection of the optimal extraction system.

This methodology has allowed to develop effective methods of sample preparation of soils, vegetables, fruits, alcoholic and soft drinks, vegetable oils, etc. for the following chromatographic determination of both hydrophilic (alcohols, glycols, certain pesticides) and hydrophobic impurities (mostly pesticides). The methods are simple and allow to obtain very pure samples, which in turn dramatically reduces limits of detection of analytes, improves repeatability of results, increases the service life period of the equipment.