On 28 August at 11:15 Ruta Hecht will defend her thesis "Novel eluent additives for LC-MS based bioanalytical methods" for obtaining the degree of Doctor of Philosophy (Chemistry).
Koit Herodes (PhD), University of Tartu, Institute of Chemistry
Karin Kipper (PhD), University of Tartu, Institute of Chemistry
Prof. Jonas Bergquist (PhD), University of Uppsala, Sweden.
The aim of this thesis was to expand knowledge about novel eluent additives used in bioanalytical chemistry using liquid chromatography-mass spectrometry (LC-MS) analysis technique. The combination of the two instruments, an LC and MS expands the limits of analytes that can be detected and quantified. However, it also introduced considerable limitations in terms of mobile phase volatility. Thus, many eluent additives which helped to increase the efficiency of LC analysis and were widely used when UV/Vis was a detector did not pass the criteria anymore. However, a promising perspective in LC-MS analysis is offered by novel fluoroalcoholic eluent additives. They are weakly acidic compounds with ion-pairing capabilities and with a positive influence on analyte ionisation in the MS source. To research the influence on retention patterns of pharmaceuticals, several novel eluent additives were tested in the basic mobile phase pH range. Different analytical column stationary phases - C18, biphenyl and pentafluorphenyl (PFP) - were investigated, both with model analytes and a large set of common toxicology screening compounds. It was observed that the use of these fluoroalcohols influenced the analysis by decreasing retention of acidic analytes and increasing retention for analytes with basic properties. Two practical applications employing novel eluent additives were developed and validated for the pharmaceuticals morphine, clonidine, midazolam, and their metabolites, as well as, for milrinone and dobutamine. The two bioanalytical methods were used to obtain data for pharmacokinetic and pharmacodynamic studies in paediatric patients. Both methods reached exceptionally low limits of quantification, with minimal sample amount used due to the positive influence of novel eluent additives on analyte ionisation.