Quantitative Content of the Parent Substance in a Complex Two-Phase Solid – Liquid System

Abstract

Drugs fabricated from medicinal plants are frequently based on parent substances comprising a mixture of two or more compounds [1]. Below, such parent substances are referred to as complexes. The ratio of components in such complex substances may vary depending on the conditions of plant growth, methods of raw material preparation (collection and storage), and the drug production technology. Sometimes, the process of isolation of biologically active compounds from raw plant materials readily yields a mixture of several components, but subsequent purification procedures aimed at obtaining single-component fractions lead to considerable losses making the production of single-component drugs unprofitable. At the same time, variability of the composition of complex substances leads to differences in the properties of drugs in various batches and poses problems in standardization of the raw materials, parent substances, and ready-to-use medicinal forms. These objective difficulties in standardization probably explain the relatively small number of drugs with multicomponent parent substances registered in many countries [2]. One way of solving the problem of obtaining complex substances with constant compositions can be via the development of methods for variation of the composition of such substances in the course of synthesis. Using such methods, it is possible to decrease the variations in the composition of raw plant materials within certain limits (technological correction), thus reducing the level of requirements on the quality of initial materials. As a rule, the parent substances (including complex ones) are obtained via crystallization or deposition from solutions. The solid substance and liquid solution are components of the two-phase solid – liquid (S – L) system. Below we will consider the influence of various factors on the ratio of components (including those with close structures) in the liquid phase of suc hS–L systems. The mass ratios of two components (A and B) in the initial substance (m 0 ) and in the solid (m s ) and liquid (m l ) phases of a two-component S – L system can be described using the following relations: