Coupling solid phase microextraction with mass spectrometry

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  • Published: Jun 30, 2016
  • Author: Rafael Lucena
  • Channels: Laboratory Informatics / Electrophoresis / Ion Chromatography / Proteomics & Genomics / HPLC / Gas Chromatography / Detectors / Sample Preparation / Proteomics / Atomic / X-ray Spectrometry / MRI Spectroscopy / Chemometrics & Informatics / UV/Vis Spectroscopy / Base Peak / Infrared Spectroscopy / Raman / NMR Knowledge Base

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Despite being 26 years old, solid phase microextraction (SPME) is in a continuous evolution which demonstrates the potential and versatility of the original idea. Currently, several research lines can be highlighted in this context such as the development of in-vivo applications and the coupling of SPME with mass spectrometry (MS).

Although there is no doubt about the usefulness of chromatographic techniques on chemical analysis, some research groups are working on circumventing the chromatographic step to make analytical methodologies faster. However, this bypass is only possible if the selectivity provided by chromatography is compensated in a different way. MS emerges as the best option of choice in this context.

Direct coupling of SPME and MS, working with atmospheric pressure interfaces, is a hot research topic in Analytical Chemistry. This coupling has been reported following two main strategies. In the first approach, the fiber is introduced in a special chamber where a flowing solvent elutes the analytes and transfers them to the MS interface while in the second approach, desorption and ionization take place simultaneously in the MS interface. Both approaches have reciprocal advantages and limitations. In this sense, in the former approach the sensitivity is limited and dependent on the volume of eluent required for the elution while in the latter the sensitivity in enhanced at the price of reproducibility. In fact, when desorption and ionization occur at the same time the signal depends on geometrical aspects (e.g. the location of the fiber into the interface) that must be precisely controlled.

Zenobi et al. have recently reported a novel SPME-MS coupling that combines the advantages of the previously described approaches. In this case, the elution and ionization are independent processes allowing the manual operation of the interface since the precision of the measurements does not depend on geometrical aspects. The main advantage of the proposal derives from the desorption step which is thermally driven instead of requiring a solvent. This thermal desorption is rapid providing narrow peaks with the subsequent sensitivity improvement. A dedicated interface, adapted from a one previously proposed by the same group, is required to achieve the coupling of SPME with a dielectric barrier discharge ionization source. The design of the interface permits the rapid transference of almost 100 % of the analytes from the SPME fiber to mass spectrometer without any carry-over between samples. This coupling has been evaluated using several drugs and pesticides as model analytes reaching limits of detection in the low pg/mL level which are better than those reported for other SPME-MS couplings.

Reference

  1. Anal. Chem. 2016, 88, 7252. Zenobi et al. Direct coupling of solid-phase microextraction (SPME) with mass spectrometry: sub-pg/g sensitivity achieved using a dielectric barrier discharge ionization source.

Blog post by: Rafael Lucena

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