Mass spectrometry is a very sensitive analytical method used for important research and for applications of analytical chemistry, particularly life science. Electrospray ionization (ESI) is generally regarded as the best-characterized and most efficient method for ionization of molecules in solution phase. The process can be conveniently divided into three stages: droplet formation, droplet evaporation and ion formation (Gaskell, S. J. Journal of Mass Spectrometry 1997, 32, 677-688). When a strong electric field is applied to a solution flowing through a mass spectrometer probe, a Taylor cone is formed at the tip of the probe, resulting in a mist of small droplets being emitted from the tip of this cone. Due to the evaporation of the free droplets and Coulombic forces, ions of sample analyte are produced. The ions enter a mass spectrometer and are subsequently analyzed.
A problem with ESI is that sample preparation is still a necessary step before ESI can be used for analysis of many types of samples. Prior to analyzing a sample by ESI mass spectrometry, the sample will undergo extraction and filtration protocols to purify the sample, for example to remove salts and detergents. Such protocols are complex, time-consuming, and expensive. Further, reagents used during the purification process can interfere with subsequent analysis of a target analyte in the purified sample. Additionally, samples that are not in solution must be dissolved as well as purified prior to ESI analysis.
More recently, the concept of ambient ionization has been developed, and now this family of ambient ionization has more than twenty members, such as desorption electrospray ionization (DESI) and direct analysis in real time (DART). Ambient ionization by mass spectrometry allows the ionization of analytes under an ambient environment from condensed-phase samples without much or even any sample preparation and/or pre-separation, offering a solution for real time and in situ analysis for complex mixtures and biological samples. These ambient ionization methods are leading are extending the mass spectrometry revolution in life science, environment monitoring, forensic applications and therapeutic analysis. However, the above described ambient ionization techniques still require pneumatic assistance, a continuous flow of solvent, and a high voltage power supply for the analysis of samples.
There is an unmet need for systems and methods that can combine sample preparation and pre-treatment and the ionization process for mass analysis of samples that do not require pneumatic assistance or a continuous flow of solvent for the analysis of the samples.