LC/MS Studies

The LC/MS research originally started in 2003 and by now the group has grown into a large unit of several sub-groups. The group is known most of all due to its studies on the fundamental aspects of atmospheric pressure ionization (API): ionization efficiencies in ESI and APCI sources as well as matrix effects. Additionally, several applications for pharmaceutical, amino acids, pesticides, etc. analyses in various matrices have been developed in the group.

Ionization efficiencies have been studied over 7 years now in this group heating up during last three to two years. Our ultimate aim is to be able to quantitatively predict the concentration of substances in the sample based on the molecular structure. Ionization efficiencies have been studied in different ionization modes: ESI positive, ESI negative, APCI positive. These studies cover a wide range of compounds, solvents, and instruments. The scales in ESI+ and ESI- range over more than six orders of magnitude. Compound choice includes pesticides, pharmaceuticals, oligopeptides as well as other compounds with various functional groups and properties. With these studies, we have described the ESI process, including proposing initial models for ionization prediction and several findings refer to very interesting medium effects. Directly linked to the ionization efficiency topic is development of derivatization reagents for LC/MS analysis, as well as novel eluent additives, specifically Hexafluoroisopropyl alcohol (HFIP) as mobile phase additive in LC/MS.

Matrix effects are also a core topic of LC/MS group. We have studied the origin of matrix effect and described its core properties, also we have proposed several measures to reduce or account for matrix effect. For example the extrapolative dilution approach.

From practical applications amino acid determination in Estonian honey has been carried out and based on this the method for determining botanical origin has been proposed. Also, we have monitored neonicotinoids content in Estonian honey and observed a significant increase in thiaclopride content in honey. Also, a number of methods for determining different pharmaceuticals (doripenem, meropenem, fluoroquinolones, sulfonamides, tetracyclines, etc) in various samples (sewage sludge, blood plasma, etc) have been developed and used in environmental and pharmacokinetic studies.

 Recently we have launched a MOOC on LC/MS validation and published a tutorial review on validation of LC/MS methods.