Theta-Channel Emitters for Nano-Electrospray and Mass Spectrometry

Abstract

Theta nano-electrospray ionization (nESI) is a new technique used in chemical and biological analysis. Interfaced with a Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer, it is becoming a powerful tool in the study of short time-scale interactions. Chemical and biochemical reactions can be studied with high spectral resolution from the moment the two solutions are brought into contact at the exit of the theta-shaped emitter. In this thesis, theta nESI emitters are fabricated from cylindrical glass tubes with an orifice shape that resembles the Greek letter "theta" (θ), which is created by a septum wall in the middle of the tube. Theta nESI emitters, pulled to a final outer diameter of ~ 4 μm, are used to demonstrate that products of homo- and heterogeneous kinetic reactions can be studied by theta nESI mass spectrometry (MS). Myoglobin (Mb) folding/unfolding and insulin-zinc complexes were used as simple model systems to study conformational changes and binding processes. Based on both experimental and theoretical results reported in this thesis, it has been suggested that mixing processes occur in the Taylor cone region rather than in the resulting droplets. Estimated reaction times from ~ 1 μs to ~ 100 ms can be achieved during theta nESI under certain experimental conditions. It has been shown that the reaction time can be controlled though various ESI parameters within the same experiment. The results reported in this thesis are focused on the practical implementation of theta nESI emitters for biological MS. These include the methods of tip optimization during the fabrication processes, the influence of geometrical parameters of the emitter tips on the physical parameters of the nESI process, and how these changes may affect chemical reactions during theta nESI. This rapid mixing technique may be extended to a number of other applications that utilize the electrospray technique such as: solar-cell fabrication, polymer fibre production, thin-film deposition, electro-spinning, and inkjet printing.