Simple chip-based interfaces for on-line monitoring of supramolecular interactions by nano-ESI MS


Brivio, Monica and Oosterbroek, R. Edwin and Verboom, Willem and Berg, Albert van den and Reinhoudt, David N. (2005) Simple chip-based interfaces for on-line monitoring of supramolecular interactions by nano-ESI MS. Lab on a Chip, 5 (10). pp. 1111-1122. ISSN 1473-0197

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Abstract:Two simple interfaces were designed and realized, enabling on-line coupling of microfluidics reactor chips to a nanoflow electrospray ionization (NESI) time-of-flight (TOF) mass spectrometer (MS). The interfaces are based on two different approaches: a monolithically integrated design, in which ionization is assisted by on-chip gas nebulization, and a modular approach implying the use of commercially available Picospray tips. Using reserpine as a reference compound in a 11 mixture of acetonitrile and water revealed that both interfaces provide a remarkably stable mass spectrometric signal (standard deviations lower than 8% and 1% for the monolithic and modular approaches, respectively). Glass microreactors, containing mixing zones, were fabricated and coupled to the modular interface with perfluoroelastomer Nanoport fluidics connectors, providing a tool to study chemical reactions on-line. Investigation of the mixing dynamics showed that complete on-chip reagents mixing is achieved within a few tens of milliseconds. Metal–ligand interactions of Zn-porphyrin 1 with pyridine ( 2), 4-ethylpyridine ( 3), 4-phenylpyridine ( 4), N-methylimidazole ( 5), and N-butylimidazole ( 6) in acetonitrile as well as host–guest complexations of ß-cyclodextrin ( 7) with N-(1-adamantyl)acetamide ( 8) or 4-tert-butylacetanilide ( 9) in water were studied by mass spectrometry using the modular NESI-chip interface. From on-chip dilution-based mass spectrometric titrations of Zn-porphyrin 1 with pyridine ( 2) or 4-phenylpyridine ( 4) in acetonitrile Ka-values of 4.6 ± 0.4 × 103 M–1 and 6.5 ± 1.2 × 103 M–1, respectively, were calculated. The Ka-values are about four times larger than those obtained with UV/vis spectroscopy in solution, probably due to a higher ionization efficiency of complexed compared to uncomplexed Zn-porphyrin. For the complexation of N-(1-adamantyl)acetamide ( 8) with ß-cyclodextrin ( 7), a Ka-value of 3.6 ± 0.3 × 104 M–1 was obtained, which is in good agreement with that determined by microcalorimetry.
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Copyright:© 2005 Royal Society of Chemistry
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