Dr. Pilleriin Peets – PhD thesis on the analysis of textile fibres and dyes

Today, on August 25, 2020, Pilleriin Peets successfully defended her PhD thesis titled Development of instrumental methods for the analysis of textile fibres and dyes.

In the thesis by Pilleriin Peets, analytical methods using FT-IR spectroscopy in ATR and reflectance modes were developed for the determination of 16 different fibre types. Additionally, classification methods (discriminant analysis and random forest) were used for the classification of unknown fibres. For the dye analysis, analytical methods using various instrumental sets (HPLC with different mass analysers, MALDI- and ESI-FT-ICR-MS) were developed based on the analysis of seven natural red dyes. 

Based on these results, a large collection of standard spectra and chromatograms was collected and made available for scientists. The advantageous developed methods were used to analyse several cultural heritage samples from the University of Tartu Art Museum, Estonian National Museum, Conservation and Digitization Centre Kanut (Estonia) and private collections. 

Well done, Pilleriin! We wish you all the best for the future!

We are happy to introduce: Dr. Piia Liigand and Dr. Jaanus Liigand

In August, additionally two of our PhD students, Piia Liigand and Jaanus Liigand, successfully defended their PhD theses. Both Piia and Jaanus worked intensively and successfully on understanding the ionization process in electrospray ionization source (ESI) and applying this knowledge for quantifying compounds with LC/ESI/MS without standard substances. Congratulations to the fresh doctors! Piia is continuing as a lab manager in TBD-Biodiscovery and Jaanus continues his scientific career at the University of Alberta in Prof. Wishart group.

On 15th of August, Piia Liigand defended her PhD thesis on “Expanding and improving methodology and applications of ionization efficiency measurements”. The opponent of Piia was Prof. Dr. Susan D. Richardson from the University of South Carolina. Over the last four years, Piia has contributed significantly into the development of ionization efficiency measurement methodology. She has been able to develop a method for measuring the ionization efficiencies for both small molecules as well as oligopeptides. Most of all, she has shown that the predicted ionization efficiencies can be applied for drug and drug-a-like measurements in the biological matrices. And, last but not least, she has pulled together a large number of response factors from the literature and shown that these values are in good agreement with each other in spite the, sometimes observed, contradicting conclusions.

Piia with her supervisors Dr. Karl Kaupmees and Prof. Anneli Kruve and opponent Prof. Susan Richardson

Jaanus Liigand defended his PhD thesis on “Standard substance-free quantification for LC/ESI/MS analysis based on the predicted ionization efficiencies”. Prof. Dr. Jonathan Martin acted as an opponent of the defense. During his PhD studies, Jaanus has worked hard on understanding the mechanism of electrospray ionization in LC/ESI/MS; primarily understanding how the structure of the compound and the eluent used in the analysis influence the ionization efficiency. Jaanus has verified, based on the largest set of ionization efficiencies measured so far (roughly 400 compounds), that the more hydrophobic compounds and more basic compounds tend to have a higher response in ESI positive mode. From the mobile phase point of view, both organic solvent content, pH of the buffer, and buffer composition, influence the ionization efficiency in ESI/MS. In general, higher organic solvent content and lower pH result in higher ionization efficiency and, therefore, a higher response in positive mode ESI/MS. Also, he investigated how well are the ionization efficiency values measured on one instrument transferable to other instruments and found that with the aid of 5-6 common compounds the ionization efficiency values can be transferred from one instrument to another. Combining these promising results and machine learning approaches Jaanus has been able to develop a truly universal approach for applying ionization efficiency predictions for quantification in suspect and non-targeted LC/ESI/HRMS analysis.

Once more – congratulation to you both!

Synthesis and characterization of novel phosphazene-based indicator molecules

On August 22, 2019 Sigrid Selberg successfully defended her PhD thesis titled Synthesis and properties of lipophilic phosphazene-based indicator molecules.

The dissertation presented by Sigrid Selberg is focused on the design and synthesis of a family of highly lipophilic phosphazene based indicators. 16 new phosphazene based indicators where phosphazene structure is extended with an azo group or with 4- (trifluoromethyl)coumarin backbone were synthesized and characterized, indicators are active in both visible absorption and fluorescence. These compounds are highly lipophilic in both neutral and protonated form, therefore, the synthesized compounds have all the desired and suitable properties to employ them in the design of an optical pH sensor. For the first time, alkyl and aryl phosphazenes are used for this purpose.

In addition, the original approach for quantifying acidity/basicity of lipophilic molecules in water-immiscible media that is at equilibrium with aqueous phase is developed and applied in the determination of biphasic pKa values of some of the synthesized compounds.

Congratulations to you, Sigrid!

From Advancements in Separation Technology to Fundamental Basicity Studies

This is the range of topics addressed on Aug 31, 2018 as PhD dissertations addressing these topics were defended at UT Institute of Chemistry by Sofja Tšepelevitš and Märt Lõkov.

Sofja Tšepelevitš (right on the photo) in her thesis titled Experimental studies and modeling of solute-solvent interactions evaluated and developed approaches for modeling intermolecular interactions in solutions and the resulting macroscopic solute properties. The applicability of the COSMO-RS method to modeling hydrogen bonding in solution was evaluated. COSMO-RS was also evaluated for its ability to predict solvent-solvent extraction. An interesting and novel issue addressed in her work besides conventional structure based property prediction was the possibility to predict liquid-liquid partitioning of solutes with unknown structure.

The thesis of Märt Lõkov titled Basicity of some nitrogen, phosphorus and carbon bases in acetonitrile is focused on obtaining high-quality basicity data (pKa data) of bases of most diverse families and rationalizing their behavior and revealing structure-basicity relationships. Nitrogen bases (N-heterocycles), phosphorus bases (halogen-substituted phosphanes) and carbon bases (substituted pentafulvenes) were included in the work.

Congratulations to both of you!

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” and in the recent paper ESI outcompetes other ion sources in LC-MS trace analysis Anal. Bioanal. Chem. 2019 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” and in the corresponding two-part tutorial review Tutorial on estimating the limit of detection using LC-MS analysis (Anal. Chim. Acta 2016, 942, 23-39, Anal. Chim. Acta 2016, 942, 40-49) 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.

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

Our warmest congratulations to Asko and Hanno!