This report describes solvent effect studies in extraction systems undertaken as part of the DTI NMS VAM programme 2000-2003.
The overall aim is to develop and apply models for the extraction of pollutants from soils. As an integral part of the project the effect of solvent strength on recovery has been based on prior research undertaken1, incorporating the Hildebrand solubility parameter. The Hildebrand solubility parameter can be sub-divided in to three components, namely, hydrogen bonding, dispersion and polarity. By a series of calculations numerical values can be obtained for environmental organic compounds and solvent alike. Then, the values can be illustrated on three-dimensional plots. This process can select the most effective solvent for extraction of a particular environmental organic compound.
The solubility parameter model will be applied to predict the recovery efficiency of environmental organic compounds, for example pesticides, from soil matrices. A GCMSD method will be developed to quantify the organic compounds. A recently developed extraction technique based on the use of pressurised solvent at elevated temperature will be used to extract the pesticides from a range of soil matrices. This technology has a great potential for improved recovery and hence reduces measurement uncertainties.
To evaluate the effectiveness of the Hildebrand solubility model requires test samples to be evaluated for a range of environmental organic compounds. To enable this to be done requires the preparation of suitable contaminated soil samples. In order to facilitate this a procedure of spiking has been adopted. Two spiking procedures have been applied, spot and slurry spiking. However, due to the inadequacy of the spiking process an evaluation of freshly spiked and aged samples have been used. This will be followed by an assessment of the performance of the basic model in real systems using Certified Reference Materials (CRM's). Future work will seek to improve the basic model. It is already known that a major contributor to retention of organic compounds on the soil is the soil components themselves e.g. humic substances and clay minerals.