Equilibrium sampling through membranes – towards online and onsite exposure measurements of available pollutants
THE PROBLEM
Many analytical methods measure the total concentration of environmental chemical pollutants. This is not necessarily a relevant measure of exposure, as chemical compounds in the environment can be bound or in other ways unavailable. A relatively new area in exposure analysis – based on simple techniques for diffusion sampling – has therefore emerged. These techniques measure the freely dissolved concentration or ultimately the fugacity or chemical activity of the compounds. The chemical activity is the driving factor for transport, distribution and bioconcentration and is therefore a key parameter for evaluation of bioavailability and toxic effects in the environment.An important principle for the measurement of freely dissolved concentrations is equilibrium sampling, where equilibrium between a sample and a sampler is attempted. If the sampler is small compared to the sample, it will not influence the conditions in the sample and the sampler will sense the freely dissolved concentration and thus the chemical activity of the measured compound. An analogy with a thermometer can be made, which senses the temperature in a sample without influencing it. Techniques for equilibrium sampling based on solid phase microextraction (SPME) were previously developed for nonpolar compounds (e.g. polychlorinated biphenyls, polyaromatic hydrocarbons). There are, however, many polar environmental pollutants (such as drug residues) of great interest which cannot be sampled using these techniques. Thus there is a need for new equilibrium sampling techniques which are suitable for these compounds. This is the background for the analytical-chemical concept “Equilibrium sampling through membranes” (ESTM), which is developed and studied in this project.
HOW CAN THE PROJECT CONTRIBUTE TO A SOLUTION TO THE PROBLEM?
The studied technique is a combination of liquid membrane extraction technique which since a number of years have been developed at Lund University and the equilibrium sampling technique for nonpolar compounds which were developed at Utrecht University and at the National Environmental Research Institute (Roskilde, Denmark). Within this project a number of techniques have been developed which permit measurements of freely dissolved fractions and chemical activity of various polar compounds and additionally of metal ions. These techniques are based on extraction in hollow fiber membranes which are simple and cheap and suitable for both laboratory and field use and permit both static and continuous measurements. WHO WILL BENEFIT FROM THE RESULTS?
Studies of freely dissolved concentrations and chemical activity are of interest for risk assessment and for a deeper understanding of distribution and effects of chemical environmental pollutants.
