In this instalment of "Sample Preparation Perspectives," Norwegian authors from the University of Oslo describe the practical aspects of hollow fibre liquid-phase microextraction in the three-phase mode (HF3 LPME). The guest authors highlight important practical issues related to the supported liquid membrane, the hollow fibre and the extraction itself. They also discuss practical work with electromembrane extraction (EME), which is related to HF 3 LPME but uses an electrical potential as the driving force for the extraction.
This month's instalment describes practical aspects of hollow-fibre liquidphase microextraction in the three-phase mode (HF3LPME). HF3 LPME is a microscale sample preparation technique (1) where target analytes are extracted from an aqueous sample through a supported liquid membrane (SLM) that is immobilized in the pores of a porous polymeric material and into a volume of acceptor solution (typically, 10–30 µL). In this context, the porous polymeric material is a hollow fibre. Here, we highlight important practical issues related to the SLM, the hollow fibre and the extraction itself because these issues are important for successful HF3LPME. We also discuss practical work with electromembrane extraction (EME), which is related to the HF3LPME device but uses an electrical potential as the driving force for the extraction (2).
How Does HF 3 LPME Work?
A 10–30 µL volume of aqueous acceptor solution is then injected into the lumen of the hollow fibre. For basic analytes, the acceptor solution is acidic, whereas it is alkaline for acidic analytes. The hollow fibre is finally placed into the sample and the whole assembly (sample vial and hollow fibre) is agitated for typically 15–45 min. During this time, analyte molecules are extracted in their uncharged state from the sample into the SLM, and further into the acceptor solution. In the acceptor solution, the analyte molecules become ionized, which prevents them from re-entering the SLM. After extraction, the acceptor solution is collected and analysed directly by high performance liquid chromatography (HPLC), capillary electrophoresis (CE), mass spectrometry (MS) or other related analytical techniques.
The major advantages of HF3LPME can be summarized as follows:
Advantages, as well as limitations, of HF3LPME have been discussed substantially in the literature and several reviews discussed a broad range of applications (4–11).