Monolithic pipette tips with integrated nanoparticles

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Solid phase extraction (SPE) is a consolidated technique in sample pretreatment thanks to its robustness, enrichment capacity and selectivity enhancement. The great variety of commercial sorbents covering a wide range of interaction mechanisms, as well as the development of novel materials makes SPE a very versatile technique. Despite its usefulness, classic SPE still presents some shortcomings such as the requirement of moderate to high sample volumes or the use of organic solvents in the milliliter range. These limitations have been faced up by different research groups and as a consequence of these efforts new techniques, for instance microextraction by packed sorbent or pipette tip extraction, have emerged.

Pipette tip extraction is based on a simple but innovative idea which consists in placing the sorbent inside a pipette tip. This approach allows the handling of low sample volumes requiring also lower volumes of organic solvents in the elution step. The sorbent can be used in different forms: immobilized in the inner walls of the tip, partially packed between two frits or forming a monolithic material. In the latter approach, the sorbent is a single piece of a porous material of appropriate polarity. The sample is passed through the material, usually in a repetitive way, to isolate the target analytes.

Monolithic materials can be of organic or inorganic nature. The combination of both natures in the same material to form a hybrid is also possible although it use has been exploited in a lesser extent. Hybrid monoliths based on the inclusion of nanoparticles as active phase are promising materials thanks to the potential (well described in the literature) of the nanomaterials. The main challenge with these materials is to achieve a good dispersion of the NPs in the monolith. If the dispersion fails, the extraction will not be efficient.

Krenkova and Foret have recently proposed pipette tips with acrylate-based monoliths including inorganic NPs in their structure for the extraction of phosphopeptides (1). The potential interaction of the target analytes with inorganic NPs, such as iron oxide or hydroxyapatite, is used to enhance the determination of the analytes by MALDI-MS minimizing the interference from non-phosphorylated peptides. Iron oxide NPs-monolithic material is prepared by flushing a colloidal solution through the monolithic support which is previously modified to introduce quaternary ammonium functionalities. On the other hand, hydroxiapatite-monolithic material is prepared following a different strategy based on encapsulation.

The extraction procedure only requires 100 µL of sample and 25 µL of eluent to achieve the enrichment of the analytes. Both materials showed a better selectivity for the extraction of phosphopeptides than the observed for commercial titanium oxide pipette tips. Moreover, the new materials can be reused several times.

We strongly recommend this article to our readers. In the original manuscript they will find the detailed synthetic procedure as well the chemical characterization of the materials.

References:

(1) Nanoparticle-modified monolithic pipette tips for phosphopeptide enrichment. Link to article


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