Agnes Heering successfully defended her PhD thesis on experimental realization of the unified pH scale

Agnes Heering successfully defended her PhD thesis on experimental realization of the unified pH scale

On December 6, 2017 Agnes Heering successfully defended her PhD thesis titled Experimental realization and applications of the unified acidity scale.

Her work literally redefines the way the pH of non-aqueous and mixed aqueous solution is understood and measured. The main focus of the experiments was on validating the measurement approach and measuring the unified pH values, i.e. pHabs values, of HPLC mobile phases (eluents). Her work introduces a conceptually new approach of measuring pH of mixed-solvent liquid chromatography (LC) mobile phases and has been published in the Analytical Chemistry journal: Unified pH Values of Liquid Chromatography Mobile Phases. Anal. Chem. 2015, 87, 2623–2630.

Mobile phase pH is very important in LC, but its correct measurement is not straightforward and all commonly used approaches have deficiencies. The new and fundamentally correct approach developed by Agnes enables direct comparison of acidities of solutions made in different solvents, based on chemical potential of the proton in the solutions.

The work by Agnes represents the first experimental realization of the pHabs concept using differential potentiometric measurement for comparison of the chemical potentials of the proton in different solutions (connected by a salt bridge), together with earlier published reference points for obtaining the pHabs values (referenced to the gas phase) or pHabsH2O values (referenced to the aqueous solution). The liquid junction potentials were estimated in the framework of Izutsu’s three-component method.
She determined the pHabs values for a number of common LC and LC-MS mobile phases and formed a self-consistent pHabs scale. This scale enables for the first time direct comparison of acidities of any LC mobile phases: with different organic additives, different buffer components etc. Agnes has developed a possible experimental protocol of putting this new approach into chromatographic practice and has tested its applicability. She has demonstrated that the ionization behavior of bases (cationic acids) in the mobile phases can be better predicted by using the pHabsH2O values and aqueous pKa values than by using the alternative means of expressing mobile phase acidity. Description of the ionization behavior of acids on the basis of pHabsH2O values is possible if the change of their pKa values with solvent composition change is taken into account.

The defence was successful in every respect. Agnes presented very well, answered questions confidently and convincingly demonstrated to everyone that she is really on top of this whole matter.

(Photo: Agnes Heering and prof. Peeter Burk, the chairman of the defence committee, during defence)

 

From high-resolution mass spectrometry in art to measurement of receptor-anion binding

Anu_Teearu_Kristjan_HaavThis is the range of topics addressed on Aug 16, 2017 as PhD dissertations addressing these topics were defended at UT Institute of Chemistry.

 

Anu_Teearu_presenting_her_PhD_ThesisAnu Teearu (left on the photo) in her thesis titled Development of MALDI-FT-ICR-MS methodology for the analysis of resinous materials addressed the analysis of resinous materials in order to obtain the maximum amount of high-accuracy data from these complex materials. Several important methodological developments (novel calibrants, novel matrix materials, etc) were introduced to MALDI-FT-ICR-MS and its capabilities were assessed during the analysis of three case study samples originating from different types of cultural heritage objects.

 

Kristja_Haav_presenting_his_PhD_ThesisThe central aim of the thesis of Kristjan Haav Quantitative relative equilibrium constants measurements in supramolecular chemistry was development of highly accurate binding constant measurement methods. The key development was measuring relative equilibrium constants instead of absolute ones, which enables eliminating or strongly reducing the influence on several error sources. Kristjan tested the applicability of this approach on two instrumental techniques: UV-vis spectrophotometry and nuclear magnetic resonance spectrometry (NMR). Comparison of the two – completely independent – techniques showed good agreement between the obtained results and thus supports the reliability of both of them.

Kristjan Haav is an alumnus of the Applied Measurement Science programme – the predecessor programme of EACH.

What is the best LC-MS ion source? How to determine Limit of detection of a method?

Asko_Laaniste_Hanno_EvardThese very important (and up to now not completely solved) questions got a lot clearer on Aug 31, 2016 as PhD dissertations addressing these topics were defended at UT Institute of Chemistry.

Asko Laaniste (left on the photo) in his thesis titled Comparison and optimisation of novel mass spectrometry ionisation sources has carried out an extensive experimental comparison of 4 different LC-MS ion sources operated altogether in 7 different modes in the analysis of 41 different pesticides. The obtained large pool of data was used for comparing the sources in terms of matrix effects, limit of detection (LoD), repeatability, linearity, signal to noise ratio (S/N) and sensitivity.

Asko demonstrated that for low levels of analytes in most cases the conventional ESI is the ion source of choice (provided the analytes are ionizable with ESI), while dopant-assisted APPI is a good alternative if low detection limits are not required and if compounds not ionizable with ESI are determined.

This is currently the most comprehensive comparison of this type available and Asko’s thesis (and the forthcoming publication) could serve as a “desk manual“ for LC-MS practitioners on choosing ion source for LC-MS analysis.

The central question of Hanno Evard’s thesis Estimating limit of detection for mass spectrometric analysis methods was: what is the best way of evaluating detection limit (LoD) of an analytical method? There are around ten widespread approaches for LoD in the literature (plus less well known ones) and the LoD values obtained using different approaches can differ by up to 10 times.

Hanno (right on the photo) carried out comprehensive analysis of the literature approaches and combined that with extensive experiments. As a result he was able to propose and convincingly justify one approach, which has merits over others and should be used for evaluation of LoD.

A two-part tutorial review on this topic is in press with the Analytica Chimica Acta journal and we expect that it will be for analytical chemists the definitive source on LoD estimation for years to come.

Hanno Evard is an alumnus of the Applied Measurement Science programme – the predecessor programme of EACH.

Our warmest congratulations to Asko and Hanno!