Mass spectrometer (MS) with electrospray ionization (ESI) coupled to a liquid chromatograph (LC) has during the recent decade become the most widespread analysis method of analysis for a vast number of microconstituents and contaminants (pesticides, mycotoxins, drug residues, etc) in a large diversity of samples (food, feed, blood, environmental samples, etc). A key component of the system is the electrospray ion source (ESI source), which converts the molecules (or ions) in the liquid phase to gas-phase ions. The mechanism of electrospray ionization (electrospray ionisation mechanism, ESI mechanism) is complex and although the ESI technique is widely used, the mechanism of ESI is still not fully understood. An important feature of electrospray is that not all molecules are readily ionized. The general principles and features of molecular structure governing the efficiency of ESI ionization are known, but there is still a long way to go until the full understanding of the process and electrospray mechanism is gained.
Chair of Analytical Chemistry of University of Tartu is strongly involved in unraveling the mystery of ESI ionization mechanism. As a tool for this an extensive scale of ionization efficiencies containing 62 compounds with ionization efficiencies ranging by a factor of about 1 000 000 has been compiled and is further supplemented by adding more compounds.
This scale was presented at the 14th Nordic MS Conference. The full presentation can be downloaded from here.
Article about this ESI ionization efficiency scale has been published in the journal Analytical Chemistry, 2010, 82, 2865-2872. Studies on ESI ionisation mechanism continue.