The Chair of Analytical Chemistry at University of Tartu

7th EuCheMS 2018 Liverpool, UK

This week two PhD students of our group, Rūta Veigure and Max Hecht had a chance to present their research in the 7th European Association for Chemical and Molecular Sciences (EuCheMS) Congress in Liverpool, organized by the European chemistry society. The conference offered a 5 day packed programme and celebrated the organization of different chemists in societies all over the world. For example, the Estonian chemical society is turning 100 years this year.

Rūta Veigure presented a poster on “Widening the range of eluent additives for LC-MS analysis to improve the retention of drug-like molecules”, while Max Hecht delivered a talk on the “The Evolution of Sponge spray for direct Sampling and Analysis by MS”.

Liverpool itself offered a variety of sights and enjoyable experiences, and as being the home-town of Beatles, there was even a chance to enjoy the tribute band “The Bootleg Beatles” during one of the Congress’ evenings.

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 (pK_a 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!

Prediction of ionization efficiencies in biological matrices

In the recent years, we have made significant progress in ionization efficiency studies. In our previous publications, we have shown that our approach can be applied in both electrospray positive and negative mode (we have recently also enabled comparing the logIE values measured in both ESI modes numerically), that our approach is transferable between different instruments with various ESI source geometries from all major mass spectrometric systems vendors, and that it is also transferable between different eluent compositions.

The logIE approach is already applicable in nice clean matrices such as neat solvents. We wanted to see if our approach also works with more difficult matrices, such as bodily fluids and tissues. The results were recently published in Analytica Chimica Acta.

In this study, we took a representative set of 10 compounds, including drugs, e.g., naproxen and lincomycin. As matrices, we used blood, plasma, urine, cerebrospinal fluid, brain and liver tissue homogenates and neat solvent to compare with. We carried out a simple and robust sample pretreatment of protein precipitation. We measured the IEs in a worst-case scenario in flow injection mode without any chromatographic separation.

As with different instrumental setups and solvents, the IEs vary between biological matrices, but the order of the compounds remains roughly the same. These variations between different matrices and variations between a certain biological matrix and neat solvent demonstrate that matrix affects ionization efficiencies and also the prediction models of ionization efficiencies. This, in turn, shows that matrix affects the importance of properties of compounds in the prediction model.

Even though the effects are big and matrix effect is strong we were happy to see that the correlations between IEs measured in the neat solvent and IEs measured in a biological matrix are in good correlation (R² from 0.7 to 0.9). These good correlations were a promising start to predict IEs in biological matrices similarly to previous predictions in the neat solvent. The most accurate model was obtained for the solvent with a mismatch of 2 times which was also expected since it is the cleanest matrix. But also for liver and brain tissues the mismatch of the model is only 3-fold.

The correlation between predicted and calculated IEs is good with the average mismatch over all biological matrices of 8 times. This means that the accuracy of standard substance free quantitation has been improved by more than an order of magnitude for the set of compounds used in this study.

More details can be found in the paper published in Analytica Chimica Acta. Piia Liigand also gave a talk on the topic in ASMS which can be found here. More papers by our group on the topic of ionization efficiencies can be found here.

Ancient men and women had different menus!

A new paper on ancient dietary practices was recently published by our group (led by Dr. Ester Oras) in the Journal of Archaeological Science: “Social food here and hereafter: Multiproxy analysis of gender-specific food consumption in conversion period inhumation cemetery at Kukruse, NE-Estonia”.

We demonstrated the fruitfulness of multiproxy dietary analysis combining plant microfossil, human bone stable isotope and pottery related organic residue analysis. The results reveal that even 800 years ago men and women had different dietary habits: men preferred fish and higher trophic level terrestrial animals (e.g. pork), whilst women declined towards ruminant carcass (a nice steak!) and dairy products.

The paper is one of the few of its kind illustrating ancient food consumption as a highly social phenomenon, and setting an example for microscale dietary analysis in the future.

Is it possible to use data below the limit of quantitation in pharmacokinetic studies?

Results below the limit of quantification (BLQ) are generally not reported or reported without explicit numbers, leaving pharmacokinetic (PK) and pharmacodynamic (PD) studies wishing for more information to improve their model parameters. But the laboratory cannot release actual values BLQ since the quality of that data has never been assessed.

Possible solutions to this unfortunate situation were investigated in a recent perspective article led by our group and published in Bioanalysis. The article titled: “Utilization of data below the analytical limit of quantitation in pharmacokinetic analysis and modelling: promoting interdisciplinary debate”, expanse the so far used statistical salvage of information, by an experimental addition to investigate the quality of data BLQ.

By directing this article towards the pharmacometrician, the analytical scientist and the regulatory personnel, we hope to encourage an inter-disciplinary discussion to improve the situation by finding ways to use BLQ data in PK/PD studies, in order to enhance the quality of the obtained pharmacokinetic models. Several ways were proposed for moving forward, in particular improving/modifying method validation guidelines for enabling to use BLQ data and leaving the decision regarding whether and how to incorporate the BLQ data into a PK/PD model to the data analyst and not the analytical chemist.

Pan-European Network of Fundamental pH Research: UnipHied

Initiated by our group, the pan-European research network of fundamental pH Research UnipHied started in May 2018.

Why is such network needed? As of now, it is not possible to compare pH values of solutions made in different solvents, as every solvent has its own pH scale. This situation is highly unfortunate, since it causes confusion and inaccuracies into many fields, extending far beyond the specific field of acid-base chemistry. Examples are industrial catalytic processes, food chemistry, liquid chromatograpy, etc. The central goal of UnipHied is to overcome this situation by putting the new theoretical concept of the recently introduced unified pHabs scale on a metrologically well-founded basis into practice.

The most important specific objectives of UnipHied are (1) to develop and validate a reliable and universally applicable measurement procedure that enables the measurement of pHabs; (2) to create a reliable method for the experimental or computational evaluation of the liquid junction potential between aqueous and non-aqueous solutions; (3) to develop a coherent and validated suite of calibration standards for standardizing routine measurement systems in terms of pHabs values for a variety of widespread systems (e.g., industrial mixtures, soils/waters, food products, biomaterials).

The first version of the pHabs measurement procedure has been created by Agnes Heering (Suu) in the framework of her PhD thesis. The main experimental difficulty is evaluation of the liquid junction potential (LJP), which will be thoroughly addressed by UnipHied. The first important steps towards this goal have very recently been made and published as two back-to-back papers: Angew. Chem. Int. Ed. 2018, 57, 2344–2347 and Angew. Chem. Int. Ed. 2018, 57, 2348–2352
The key achievement described in the papers is finding an ionic liquid, namely [N2225][NTf2], that can be used as salt bridge electrolyte and has such properties that two out of three main sources of LJP are eliminated.

The partners of the UnipHied network are LNE (France, coordinator), BFKH (Hungary), CMI (Czech Republic), DFM (Denmark), IPQ (Portugal), PTB (Germany), SYKE (Finland), TÜBITAK-UME (Turkey), Freiburg University (Germany), ANBSensors (United Kingdom), FCiencias.ID (Portugal), UT (Estonia).

UnipHied is funded from the EMPIR programme (project 17FUN09) co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

ASMS 2018 in San Diego

On 3rd-7th June three members of our group focusing on ionization efficiency studies Dr. Anneli Kruve-Viil, PhD students Piia Liigand and Jaanus Liigand, participated in the 66th Annual Conference of American Society for Mass Spectrometry (ASMS) in San Diego, CA. The conference was a huge success. There were altogether about 7500 scientists participating, ca 200 oral presentations and 3300 of posters. We had two oral presentations and one poster presentation.

The conference was kicked off by a presentation by Lisa Shipley from Merck who gave a very informative talk about smart trials and moving to patient-centric clinical trials – most probably the future of clinical trials. It was very inspiring to see how a field that is considered to be relatively conservative is picking up the most modern technical solutions such as clever packages and home-based sample collection.

The first full day of the conference started with a presentation by our PhD student Piia, who gave a talk about achieving more accurate semi-quantitative analysis by predicting electrospray ionization efficiencies. She first gave an overview of the research carried out so far and then, introduced her latest results. She showed that with the help of using ionization efficiencies, concentration estimation in various biological matrices was improved by more than an order of magnitude.

Jaanus presented a poster on semiquantitative LC/ESI/MS via ionization efficiency prediction. He presented the simple and user-friendly approach of predicting ionization efficiencies using only 2D structures. We are now able to predict ionization efficiencies in both ESI positive and negative mode and in different solvent compositions without time-consuming DFT-COSMO calculations. Additionally, we have shown that using ionization efficiency predictions the validation with LC gradient elution resulted in 2.7-fold mispredicted concentrations compared to 44-fold mispredictions using directly peak areas. We were happy to see that numerous groups were interested in our studies and fruitful discussions about the results did not stop until the end of the poster session.

Dr. Anneli Kruve-Viil presented some of the latest results obtained in FU Berlin. She talked about using mass spectrometry and ion mobility spectrometry for investigating interlocked nature of catenanes and knots. These results will soon be shared with everyone.

In conclusion, this year’s ASMS was very successful for our group. We saw a lot of interest in our work, met our collaborators and got some new friends and possible future collaborators. We are already looking forward to the next ASMS in Atlanta. We are also grateful for our financial supporters, who made this conference possible to us: instrumentation provided by Estonian Center of Analytical Chemistry (www.akki.ee), Ministry of Education and Research of Estonia by smart specialization doctoral stipend, Graduate School of Functional Materials and Technologies, and Alexander von Humboldt Foundation.

More information about the group focusing on ionization efficiency studies can be found on the webpage kruvelab.com

Bachelor’s and Master’s Defences 2018

Traditionally, in the first half of June, our bachelor and master students defend their theses. This year there were 3 masters students and 2 bachelor students from our group. Here is how the students described their theses.

Alo Rüütel “Synthesis of bambusuril macrocycles and investigation of their binding properties”, master’s defence
In my master’s thesis, I synthesized bambusuril macrocycles. These receptor molecules are very potent anion binders. Usually, molecular receptors do not function in water because they are not able to bind target molecules with sufficient strength. Some bambusuril derivatives are able to function in aqueous media, which makes them a very special type of macrocyclic receptors. It is possible to use these molecules as ionophores for anion selective electrodes.

Ernesto de Jesus Zapata Flores “Determination of free diisocyanates in polyurethane foam”, master’s defence
My thesis focused on the test of a proposed method to analyze free diisocyanates in polyurethane foams for two reasons, by one side those compounds can represent a danger if care is not taken when the foam is used, and by the other side, new legislation is more aggressive against those compounds. The method is a simpler alternative to achieve the derivatization of diisocyanates.

Andre Leesment “Gas phase acidity measurements of superacids using FT-ICR method”, master’s defence

My master’s thesis was based on gas-phase acidity measurements of some very strong acids. Such strong acids are widely used in organic synthesis as reactants and/or catalysts. The anions of such acids exhibit high stability, which makes the valuable components of contemporary energy storing devices. The obtained results allow us to work on expanding the self-consistent gas-phase acidity scale with acids stronger than the ones experimentally measured so far.

Lisett Kiudorv “Quantitative analysis of clay components using ATR-FT-IR spectroscopy”, bachelor’s defence
The main purpose of my bachelor’s thesis was to develop a method that enables quantitative analysis of clays using ATR-FT-IR spectroscopy combined with the chemometric partial least squares method. The developed method is quick and easy to use and reduces the required sample size to around a milligram. The dramatic decrease in sample size makes it possible to analyse samples from archaeology and art. The method was then used to analyse six archaeological samples including one of the oldest potteries found in Estonia and an Egyptian pottery, which holds a bird’s mummy.

Elisabeth Parman “Determination of pK_a values of fluorocompounds in water using ¹⁹F NMR”, bachelor’s defence
The main aim of my bachelor’s thesis was to determine pK_a values of fluorocompounds in water using ¹⁹F NMR. This method is not particularly commonly used, but it can be used to verify or disconfirm values that have been measured with different methods, especially in cases where the measurements with other methods are problematic. For example, the purity and accurate concentration of the measured compound need to be concerned for most of the methods, but with ¹⁹F NMR it is not problematic.

Comparative validation of amperometric and optical dissolved oxygen sensors

A comprehensive comparative validation for two different types of dissolved oxygen (DO) analyzers, amperometric and optical, together with estimation of measurement uncertainty is presented in the recently published article I. Helm, G. Karina, L. Jalukse, T. Pagano, I. Leito, Environmental Monitoring and Assessment 2018, 190, 313.

A number of performance characteristics were evaluated including drift, intermediate precision, accuracy of temperature compensation, accuracy of reading (under different measurement conditions), linearity, flow dependence of the reading, repeatability (reading stability), and matrix effects of dissolved salts. The matrix effects on readings in real samples were evaluated by analyzing the dependence of the reading on salt concentration (at saturation concentration of DO). The analyzers were also assessed in DO measurements of a number of natural waters. The uncertainty contributions of the main influencing parameters were estimated under different experimental conditions. It was found that the uncertainties of results for both analyzers are quite similar but the contributions of the uncertainty sources are different.

The results imply that the optical analyzer might not be as robust as is commonly assumed, however, it has better reading stability, lower stirring speed dependence, and typically requires less maintenance. On the other hand, the amperometric analyzer has a faster response and wider linear range.

(Photo by Lauri Jalukse: measurements of dissolved oxygen concentration with amperometric and optical analyzers at Jordan spring, Karksi-Nuia, Estonia)

Measurement uncertainty online course (MOOC) 2018 edition successfully finished!

On May 14, 2018 the on-line course (MOOC) Estimation of measurement uncertainty in chemical analysis offered by University of Tartu finished successfully.
Eventually altogether 521 people registered (270 in 2014, 489 in 2015, 757 in 2016, 363 in 2017) from 76 countries (a number of participants joined after the start of the course). 358 participants actually started the course (i.e. tried at least one graded test at least once) and out of them 218 successfully completed the course (141 in 2014, 169 in 2015, 308 in 2016, 148 in 2017). The overall completion rate was 42% (52% in 2014, 34% in 2015, 40% in 2016, 41% in 2017). The completion rate of participants who started the studies was 61% (67% in 2014, 60% in 2015, 67% in 2016, 68% in 2017). The completion rates are nicely consistent over the last years and can be considered very good for a MOOC, especially one that has quite difficult calculation exercises, which need to be done correctly for completing the course.

The participants were very active and asked lots of questions. The questions were often very much to the point and addressed things that are really important to analysts in their everyday work. The course has several forums (general and by topic) and the overall number of posts to them during the course period reached almost 300 (!) (overall number of posts, both from participants and from teachers) and the forums are still active and posts are still coming in.

This active participation made teaching of this MOOC a great experience also for us, the teachers. The discussion threads gave a lot of added value to the course and some of them triggered making important modifications to the course materials, even during the course.

We want to thank all participants for helping to make this course a success!

We plan to repeat this course again in Spring 2019.