Abstract
Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are of fundamental importance to biomolecular analysis. Previously, electrospray ionization (ESI) and matrix assisted laser desorption-ionization (MALDI) have been the main ionization methods used. Surface acoustic wave nebulization (SAWN) is a new technique that has been demonstrated to deposit less energy into ions upon ion formation and transfer for detection than other methods for sample introduction into a mass spectrometer (MS). Here we report the optimization and use of SAWN as a nebulization technique for the introduction of samples from a low flow of liquid, and the interfacing of SAWN with liquid chromatographic separation (LC) for the analysis of a protein digest. This demonstrates that SAWN can be a viable, low-energy alternative to ESI for the LC-MS analysis of proteomic samples.
Highlights
Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are of fundamental importance to biomolecular analysis
In order to demonstrate that Surface acoustic wave nebulization (SAWN)-mass spectrometer (MS) is capable of detecting peptides of different physicochemical properties and concentration in mixtures in flow mode, we analyzed a mixture of Glu-1 Fibrinopeptide B (GluFib, EGVNDNEEGFFSAR), an ionizable and generally multiply-charged peptide and ALILTLVS, a more hydrophobic and generally singly-charged peptide, at a 50:1 mM concentration respectively in infusion mode at 5 mLmin-1
The main reasons that electrospray ionization (ESI) has been widely adopted as an MS ionization technique is that it is able to ionize and introduce into the gas phase labile, polar, non-volatile molecules, such as proteins and peptides, at relatively low energy, maintaining the integrity of these biomolecules, and that it can be coupled online to liquid chromatography to harness the high resolution separation power of this technique to analyze complex mixtures of molecules
Summary
Soft ionization methods for the introduction of labile biomolecules into a mass spectrometer are of fundamental importance to biomolecular analysis. Surface acoustic wave nebulization (SAWN) is a new technique that has been demonstrated to deposit less energy into ions upon ion formation and transfer for detection than other methods for sample introduction into a mass spectrometer (MS). The identification of alternative low-energy ionization methods is needed either for specialized applications or to address the shortcoming of ESI, and this has led to the development of cold-spray[20] and other sources[21] For these methods to be generally useful it is highly advantageous if they can be interfaced with liquid flow methods, especially with liquid chromatography which has become a fundamental and integral part of MS workflows for proteomics and metabolomics. We report here the use of a simple flow interface for sample introduction via SAWN, examine the effects of flow and concentration on MS data quality, and show for the first time that SAWN can be effectively interfaced with liquid chromatography with gradient elution for the analysis of mixtures by MS
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