Magnetic solid phase extraction coupled to ambient ionization mass spectrometry

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Direct coupling of microextraction techniques and ambient ionization mass spectrometry opens a door to rapid, selective and sensitive analyses that are quite attractive in the bioanalytical field. The use of nanoparticles (NPs) in this combination may be problematic since they are not fully compatible with MS although they have a great potential as sorbent in microextraction techniques. In fact, these NPs may be blown during the ionization step causing the entering of this material in the spectrometer.

Prof. Yu-Qi Feng and coworkers have recently proposed the use of magnetic NPs (MNPs) for this arrangement avoiding the previously mentioned shortcoming. The extraction protocol follows the typical workflow of a dispersive solid phase extraction (DSPE). In short, the MNPs are dispersed into the sample to favor the interaction/isolation of the analytes. Afterwards, they are cleaned-up with an appropriate solvent and finally recovered in a special capillary for instrumental analysis. This step, the absence of a chemical elution, makes different this approach from classic DSPE.

Simpler is better
The magnetic glass capillary employed for the MNPs recovery and introduction into the MS interface is the core of the proposed coupling. It is lab-made and according to the authors is simple to be constructed. It consists of a glass capillary of 2.2 mm of inner diameter which is closed at the end by burning. Finally, a magnetic disk is attached to this end to aid the MNPs recovery.

The magnetic capillary can be inserted in the desorption corona beam ionization source where the plasma generated interacts with the MNPs surface desorbing/ionizing the targets. During the whole process, the MNPs remain attached to the capillary by magnetic forces.

Application to bioanalysis
Our colleagues have applied this combination to determine several antidepressant drugs in human fluids using polypyrrole coated MNPs as sorbents. The limits of detection as low as 0.2 ng/mL in urine indicate the potential of this idea.

We strongly recommend our readers to go through that article published in The Analyst. You will enjoy reading it and you will find additional information to this excerpt.

References:
(1) Magnetic solid phase extraction coupled with desorption corona beam ionization-mass spectrometry for rapid analysis of antidepressants in human body fluids. Link to the article
(2) Supplementary info of the article. Link to the info

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