Novel Atmospheric Biomolecule Ionization Technologies

In general, atmospheric ionization is defined as an ionization process outside of the mass spectrometer vacuum chamber. During the past two decades, several novel atmospheric ionization methods were developed. Nevertheless, they can be divided into two major categories. One is direct analysis at real time (DART) and the other is modifications on electrospray ionization (ESI). In addition, some methods are used to analyze samples directly without any pretreatments. Those methods are often called as ambient ionization methods. Many atmospheric ionization methods are also considered as ambient ionizations. DART and desorption electrospray ionization are examples. Nevertheless, most atmospheric ionization methods involve the need of high voltage outside of the mass spectrometer vacuum chamber. In this review, we will only briefly introduce most of the existing methods which need high voltages. Most effort will be placed on the newly developed novel methods which do not need high voltages. They include Ultrasound Ionization (UI), Triboelectric Spray Ionization (TeSI) and Kelvin spray ionization (KeSI). These ionization methods don’t need to have any external high voltage power supply for ionization. They have the advantages of very soft ionization to keep bio molecular ions more similar to the structures in solution phase. Some related mechanisms will also be discussed.