Our Research

Liquid-phase microextraction (LPME)

LPME is a microextraction technique aimed for extraction and enrichment of chemical substances of interest (analytes) from a given sample, prior to measurement by chromatography, electrophoresis, mass spectrometry, or atomic spectroscopy. We mainly explore LPME for pharmaceutical and biomedical analysis, and therefore the 

analytes in our research are pharmaceuticals (and related substances). These are drug substances, metabolites, drugs of abuse, doping agents, and therapeutic and diagnostic peptides and proteins. Samples are typically blood, urine or saliva. There is considerable interest for LPME internationally, and this work is not limited to pharmaceutical and biomedical analysis. Thus, LPME is among others explored for environmental analysis, and for testing of foods and beverages.

Our research group invented LPME in 1999 [1]. Figure 1 illustrates the principle of LPME performed with commercially available 96-well technology [2]. In LPME, we take advantage of the fact that most pharmaceuticals are much more soluble in water in their ionized form than in their neutral form.

First, we fill the sample into the sample well. The sample volume is typically 25-250 µL. Second, for extraction of basic analytes, we add base to the sample and the analytes are converted to their neutral form. Third, 2-5 µL of an organic solvent immiscible with water is pipetted into a small polymeric filter disk, and this is placed in close contact with the sample. The organic solvent serve as supported liquid membrane (SLM), and is immobilized in the porous structure of the filter by capillary forces. The SLM is only 100 µm thick. On the other side of the SLM we fill acceptor solution (20-100 µL), and this is typically a dilute aqueous solution of formic acid. The entire extraction system is agitated for 15-60 minutes, and the analytes are extracted in their neutral form into the SLM, and further into the acceptor solution. Because the acceptor solution is acidic, the analyte molecules are converted to their ionized form (protonation), and they are trapped here. After extraction, we collect the acceptor solution and analyse it, typically by liquid chromatography-mass spectrometry (LC-MS). For extraction of acidic analytes, the pH gradient across the SLM is reversed; the sample is acidified and the acceptor solution is alkaline. Major advantages of LPME with 96-well technology include:

• Very efficient sample clean-up
• Acceptor solution is aqueous and can be injected directly into LC-MS
• Analyte enrichment
• High-throughput and automation
• Low cost
• 2-5 µL organic solvent per sample = green chemistry

LPME has been explored for long time by academic institutions, and a large number of applications are found in scientific journals. Due to the advantages mentioned above, we think LPME has potential for implementation in routine laboratories. Therefore, we currently focus all our LPME research on activities required for such routine implementation. We work with commercially available 96-well plates and automation, and we develop generic methods for different classes of pharmaceuticals. Also, we work with calibration procedures, to make sure that analytical data are reliable when obtained from methods using LPME. We publish our data in scientific journals. 

Electromembrane extraction (EME)

We also do research on electromembrane extraction (EME), and this research is more of fundamental character. EME is similar to LPME, but in EME the driving force for extraction and mass transfer in an external electrical field (DC) applied across the SLM. EME was invented by our research group in 2006 [3], and the principle is illustrated in Figure 2.

For basic analytes, the sample is neutral or acidic to ensure that the analyte molecules are in their ionized form. The positive electrode is inserted in the sample. The acceptor solution is also neutral or acidic (and aqueous), and here the negative electrode is inserted. As in LPME, the sample and the acceptor solution are separated by a supported liquid membrane (SLM). Extraction is performed by application of the electrical potential, by simultaneous agitation of the entire extraction system. Extraction is terminated by turning off the external power supply, and the acceptor solution is collected measurement (typically performed by LC-MS).

EME is fundamentally different from LPME by the fact that mass transfer is by electro-kinetic migration. The advantage of electro-kinetic migration is that mass transfer is rapid, and that mass transfer can be controlled by the direction and magnitude of the electrical field. Thus, EME enables rapid and very selective extraction. We also operate EME in 96-well format, and major advantages include:

Unique for EME

• Mass transfer and selectivity can be controlled by voltage polarity, voltage magnitude, SLM composition, sample pH, acceptor solution pH.

Common With LPME

• Acceptor solution can be injected directly into LC-MS
• Analyte enrichment
• High-throughput and automation
• Low cost
• 2-5 µL organic solvent per sample = green chemistry

Electro-kinetic migration within an organic liquid membrane and electro-assisted partition in and out of said membrane has not been characterized previously. Therefore, a large part of our EME research is about understanding all the fundamentals, and especially about how to design the chemistry of the SLM for different type of analytes. In addition, we also develop applications of EME for pharmaceutical and biomedical analysis, to illustrate the potential of the concept. Currently, we focus on EME of very polar small-molecule substances and on peptides. Such analytes can often be difficult to handle by existing sample preparation techniques, and we think there is a great potential for EME here.

We have a strong feeling that the principle of EME (electrophoresis across an oil membrane) will be used in the future, for sample preparation with chromatography and mass spectrometry. Furthermore, the use of smartphones and other small measuring devices are expected to increase in the future, but for such systems to work with complex samples, sample preparation based on microextraction has to be performed. This is where we think EME fit perfectly; small size, cheap, compatible with dirty samples, and controlled by electrical potentials… EME has been commercialized by a Norwegian company, and the first generation equipment was launched in June 2022.

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