The most comprehensive collection of rigorously measured pH values of mobile phases in reversed-phase liquid chromatography

During recent years, we have been engaged in extensive investigations of the unified pH (pHabs) values of reversed-phase liquid chromatography (RPLC) mobile phases. The pHabs scale has the advantage over the conventional pH scale because pHabs values express acidity in terms of the thermodynamic activity of the solvated proton. Therefore, pHabs values are directly comparable between solvents/media of different compositions. At the same time, pHabs is convenient to use, as pHabs values of aqueous solutions are equal to the respective conventional pH values.

This comparability is especially useful in RPLC, as mobile phases are mixtures of water with organic solvents in different ratios. Thus, it can be said that pHabs is the best way of expressing pH if a rigorous comparison of pH between solutions in different solvents is needed.

As a result of our work, we have carefully measured the pHabs values of 78 mobile phases commonly used in RPLC, using around 300 individual ΔpHabs measurements between different mobile phases (see the “ladder” scheme below). This is, to the best of our knowledge, the most comprehensive collection of rigorous pHabs values of RPLC mobile phases and has now been published as A. Heering, M. Lahe, M. Vilbaste, J. Saame, J. P. Samin, I. Leito. Improved pH measurement of mobile phases in reversed-phase liquid chromatography. Analyst 2024.

The ΔpHabs values were measured by differential potentiometry, using potential differences in a symmetric cell with two glass electrode half-cells (see figure above) and almost ideal ionic liquid triethylamylammonium bis((trifluoromethyl)sulfonyl)imide [N2225][NTf2] salt bridge with multiple overlapping measurements. The system of altogether 300 ΔpH values, pictured in the “ladder” scheme below, was anchored to the pH value of standard pH 7.00 aqueous buffer solution.

In addition, a simpler measurement method that uses double junction reference or double junction combined electrodes was tested and was found suitable for routine laboratories. The results show that the design of the junction is an important factor in deciding if the electrode can be used for unified acidity measurements. This is the first successful use of double junction combined electrodes filled with ionic liquid for the measurement of pHabs values.

The article is featured in the themed collection Analyst HOT Articles 2024.

The Institute of Chemistry was recognized for improving the quality of education

The Institute of Chemistry received an award for its consistent and systematic efforts over the past three years to improve the quality of education.

One of the main goals was to develop students’ skills in specific subjects by changing teaching methods and involving students more actively in learning. For that, seminars were organized together with the teachers, which led to the realization that also the subjects of the lectures needed to be adjusted and coordinated with each other. Student feedback was used to improve courses, and the online learning platforms were updated. In parallel, the entire curriculum was revised.

Chemistry Master program director Edith Viirlaid and Vice-Rector Aune Valk

According to the Vice-Rector Aune Valk, the award recognized the Institute’s systematic and integrative approach to improving the quality of education. She emphasized the importance of consistent work for keeping the students engaged by active learning and motivating the students by making education more interactive and relevant to future careers. She also highlighted that there has already been a positive response from the students who appreciated the improvements.

In the University of Tartu, the award for improving the quality of education acknowledges a university institute, college, or department for their successful planning and implementation of activities that enhance the quality of learning. It is important that these initiatives include the collaboration between the faculty and students. Here is the original post in Estonian.

The cultural heritage investigation workgroup published the first Tutorial Review article about lasers!

The analytical chemistry scientists (Dr Signe Vahur, Dr Anu Teearu-Ojakäär, Prof Ivo Leito) together with physicists (Dr Rünno Lõhmus, Dr Aleksei Treshchalov, Prof Jaak Kikas) from the Institute of Physics at the University of Tartu and conservation scientists at the Estonian Academy of Arts (Prof Hilkka Hiiop, MSc Käthi Niman), have published a new tutorial review article, “Laser-based analytical techniques in cultural heritage science – Tutorial review“ in the journal of Analytica Chimica Acta. The article is available here: https://doi.org/10.1016/j.aca.2023.342107.

Graphical abstract in the journal of Analytica Chimica Acta (https://doi.org/10.1016/j.aca.2023.342107)

This comprehensive collaboration article is significant for the cultural heritage investigation workgroup and the PRG1198 project team, which is currently developing a new laser-based MS system.

The main focus of this tutorial review is to give a simple and accessible overview of the physical background of different lasers, their parameters, and examples of applications in analytical techniques useful for the identification of components of various complex materials from a cultural heritage point of view. Besides conservators and cultural heritage scientists, this review may also interest researchers and students of other fields (e.g., material science, physics, chemistry, forensics, etc.) who wish to know more about lasers.

Congratulations on the ERC Consolidator Grant!

We are delighted to announce that the prestigious ERC Consolidator Grant 2023 was awarded to a former member of our Analytical Chemistry group, Associate Professor Anneli Kruve at Stockholm University!

Anneli Kruve

The European Research Council (ERC) Consolidator Grant is aimed to support early-career researchers to consolidate their own independent research team or program over the next five years. We are very proud that this year one of the awardees was Anneli Kruve, Associate Professor at Stockholm University and head of the Mass Spectrometry Laboratory. In her research, she combines analytical chemistry with modeling and machine learning. The goal of the ERC funding is to support the research of her group on developing broader and more accurate methods to characterize and measure toxic chemicals in environmental samples. 

Only a few percent of chemicals that cause the toxic activity of environmental samples are currently known. In this project, Anneli and her group will combine high-resolution mass spectrometry and machine learning to find novel toxic chemical structures, which enables focusing the toxicity research on chemicals that truly matter. Understanding the emission and transformation processes of toxic chemicals is a necessary step to decrease the chemical risks in the environment. 

More information about the research performed by Anneli’s group can be found on the Kruve lab webpage. 

Two new biomolecular studies of early farming by the Archemy group

Our Archemy group has recently published two major collaborative articles about the arrival and spread of early farming in NE Baltic.

Based on pottery lipid residue and dietary stable isotope analysis combined with zooarchaeological data and archaeobotanical studies, it was shown that farming arrived in the NE Baltic with migrating Corded Ware cultures in the early 3rd millennium cal BCE, but here this new subsistence strategy relied on stockbreeding rather than crop cultivation.

Early farmers in the NE Baltic were exploiting both domesticated and wild species, whilst the introduction of domesticates had little if any impact on local hunter-fisher-gatherer communities who remained true to their forager lifeways. There was no clear transition from foraging to farming in the 3rd millennium cal BCE NE Baltic, instead we see separated communities and parallel worlds of local foragers and incoming early farmers practicing mixed economy. However, the lipid residue data in the wider Baltic context shows several regional variations in the arrival and spread of early farming practices.

Read full articles here:

Oras, E., Tõrv, M., Johanson, K, Rannamäe, E.  et al. 2023. Parallel worlds and mixed economies: multi-proxy analysis reveals complex subsistence systems at the dawn of early farming in the northeast Baltic. R. Soc. open sci. 10230880230880. http://doi.org/10.1098/rsos.230880

Lucquin, A., Robson, H. Oras, E. et al. 2023. The impact of farming on prehistoric culinary practices throughout Northern Europe. PNAS. 120 (43) e2310138120. https://doi.org/10.1073/pnas.2310138120

The laureates of the Ann Mihkelson’s scholarship have been announced!

Elisabeth working

This year, the laureate of the Ann Mihkelson’s scholarship is Elisabeth Parman!

The scholarship was founded in 2011 by Anu Ebbe Mihkelson and its purpose is to support female scientists and doctoral students, especially chemists, with their research or supervision of master’s and doctoral students. We are happy to announce that this year, the scholarship was awarded to a young researcher from our Chair of Analytical Chemistry group – junior researcher/doctoral student Elisabeth Parman.

Congratulations from all of us to you, Elisabeth!

 

A biomolecular revolution is taking place in archaeology!

Opening day of the IBSA 10th meeting at the Estonian National Museum (Photo: Peeter Paaver)

Although archaeology has been inherently interdisciplinary from its early years, recent decades have seen changes referred to as the third scientific revolution in archaeology. Innovative methods enable us to answer previously unanswered questions and pose new ones about the past. 

Biomolecular archaeology brings together archaeologists, historians, biologists, and chemists. From September 13th to 15th, the tenth International Symposium of Biomolecular Archaeology (ISBA10) took place at the Estonian National Museum in Tartu. The conference provided a comprehensive overview of the field, covering various research topics, from the domestication of different species to ancient diseases and migrations, as well as the methods employed. The conference abstracts are available here. 

The material heritage studied through biomolecular archaeology methods is an irreplaceable resource. Therefore, it must be treated sustainably – obtaining maximum information with minimal damage. For example, it is possible determine the species of a bone to simply by rubbing its surface with an eraser (ZooMS). Still, we must continually justify the use of human remains as research resources, and ask whether the scientists’ perspective aligns with the institutions curating collections, as Rita Peyroteo-Stjerna reminded us. When analysing ancient materials, it is important to leave a mark. The field of biomolecular archaeology is increasingly recognizing the need for data standardization and accessibility, as demonstrated by James Fellows Yates in his presentation on a community-based approach to data integration. 

Ester Oras putting up her poster (Photo: Peeter Paaver)

Genetics, one sub-field of biomolecular archaeology, is rapidly evolving. It no longer focuses solely on major migrations. New technologies offer insights into ancient diseases, the environment, and even the presence of people where their remains are absent. For example, today we can obtain information about people from ancient chewing-gums or worn jewellery.  Also, social structure and kinship is analysed in collaboration with archaeologists.  

The molecules of lipids, proteins, and carbohydrates have been preserved in various ancient objects as burnt food crust or by being absorbed into pots, in animal and human bones, and other tissues, as well as in plants. While stable isotope analysis of bulk collagen provides a general picture of the diet, stable isotopes of individual amino acids allow distinguishing between terrestrial and aquatic origin of proteins. 

Biomolecular archaeology cannot be the domain of nerds quietly working in the lab. Both keynote speakers at the conference, Anne Stone and Carl Heron, provided a broader insight into the developments of biomolecular archaeology. The former focused on one catalyst of the revolution, ancient DNA research, the significance of which for society was highlighted by the Nobel Prize awarded to Svante Pääbo in 2022. Carl Heron provided an excellent framework for the history of biomolecular archaeology and urged the community to think more about bringing scientific results to the public. 

Over 400 participants attended the ISBA 10th meeting (Photo: Peeter Paaver).

The conference was organized by: the University of Tartu and the Geenikeskus Foundation. 

The organization of the conference was supported by: the Collegium for Transdisciplinary Studies in Archaeology, Genetics, and Linguistics of the University of Tartu, the Faculty of Arts and Humanities, the Faculty of Science and Technology; the International Society for Biomolecular Archaeology (ISBA); the city of Tartu; the European Union through the PaleoMIX (No 101079396) and cGEM (No 810645) projects. 

Dr. Shidong Chen – thesis on the organic residue analysis

Shidong Chen, successfully defended his PhD dissertation entitled “Unravelling prehistoric plant exploitation in eastern Baltic: organic residue analysis of plant-based materials by multi-method approach” on the 12th of September. We were honored to have Dr. Shinya Shoda from Nara National Research Institute for Cultural Properties, Japan as Shidong’s opponent.

From left to right: opponent Dr. Shinya Shoda, Dr. Shidong Chen, supervisors Dr. Ester Oras and Prof. Ivo Leito

Shidong’s PhD work is aimed at discovering plant exploitation in the ancient eastern Baltic area with a focus on two types of plant-derived materials: resinous materials and dietary plants. The main innovations are developing multi-methodological approaches and interpreting multi-proxy datasets with chemometric and statistical methods.

For identifying the composition of resinous adhesives, ATR-FT-IR analysis was conducted in combination with a PCA-based DA classification model for further compositional and spatial/temporal classification. This method can help simplify IR spectra interpretation and reduce the need for GC-MS analysis.

For identifying dietary plants, a multi-method approach was applied by plant micro fossil analysis and EA-IRMS combined with ORA. EA-IRMS can provide preliminary origins of samples with plant and/or animal bases. Plant micro fossil analysis and ORA in complementary can identify the species of plant remains. Correspondence analysis further compares and indicates the agreement of the three methods and visualizes the correlations between the multi-proxy data.

Dr. Shidong Chen moments before the presentation

The plant exploitation in prehistoric easter Baltic shows different patterns with dedicated multi-method case studies on several Stone Age, Bronze Age, and Iron Age sites. In the Stone Age, plant exploitation was more technological (adhesives and resinous compounds) than dietary-related. The plant consumption for dietary purposes became more abundant in the Bronze Age. The major changes happened with the Iron Age displaying a more diverse plant-based diet with more inclusion of C3 cereals (e.g., wheat and barley), yet the spread and cultivation of C4 millet may not have emerged in this region.

Shidong is currently working at ARCHEMY lab as a lab technician at the University of Tartu. He will continue his journey discovering ancient food ways from pots and bones.

Dr. Ernesto de Jesus Zapata Flores – PhD thesis on LC-MS derivatization reagents

Last Wednesday, August 30th, 2023, a moment that marks the culmination of years of hard work and determination of Ernesto de Jesus Zapata Flores – an AMS alumnus. He successfully defended his PhD thesis titled Derivatization Reagents used in negative mode electrospray LC-MS. The opponent was Associate Professor Jeffrey Hawkes from the University of Uppsala, Sweden.

In the vast application of derivatization reagents in RPLC-UV and RPLC-MS positive mode, Ernesto’s thesis delved into the question: What about LC-MS negative mode? Why don’t we compare both modes and see the best of both worlds?

Firstly, the thesis has been inspired by DEEMM – a commercial reagent – which also was one of the earliest reagents studied in our department. The comparison of the ionization mode in the determination of free amino acids in beers showed that (1) the matrix effects were less severe in the negative mode.

Later on, the method applying two azobenzene-based reagents, which were called AzoB and AzoC  (synthesized in our lab), has been fully developed specifically for LC-QqQ. The “gourmet” part that Ernesto has brought to the table of the analytical chemistry community was the study of (2) MS/MS fragmentations of all three reagents with different amino compounds in both ionization modes.

Moreover, his thesis has demonstrated comprehensive research about (3) optimization for the derivatization process and the ion source, (4) the confirmation of reaction yields, and (5) the correlation between ionization efficiency and LOD/LOQ of derivatives. Finally, applications of the validated method (7) for real-world samples (different beverages: beers, Kali, juices) and (8) neutral loss scan have been showcased.

Alongside the road, (9) side reactions managed to be worth some of his sweat and tears. At the end of his PhD journey, he (10) evaluated an identification tool using the transition of derivatives in both MS polarities.

10 out of 10 – that should be given for Ernesto’s dedication on the road to becoming an expert in LC-MS derivatization. Congratulations, Ernesto! We eagerly await your next academic steps. Hopefully, all your goals will be achieved.

Dr. Signe Vahur’s visit to the Smithsonian Museum Conservation Institute labs!

Dr. Signe Vahur, during her vacation to Washington DC, USA, had the possibility to visit the Smithsonian’s Museum Conservation Institute (MCI) labs.

The MCI is the center for specialized technical collection research and conservation for all Smithsonian museums and collections. MCI combines knowledge of materials and the history of technology with state-of-the-art instrumentation and scientific techniques to provide technical research studies and interpretation of artistic, anthropological, biological, and historical objects (webpage: https://mci.si.edu/).

Dr. Asher Newsome, a physical scientist at MCI, kindly showed her the research labs equipped with different analytical instruments (e.g., chromatographs (GC, LC), mass spectrometers, spectrometers (FT-IR, Raman, SEM-EDS)) and labs for conserving paintings, textiles, and paper items. He introduced some of his research work, and they had a good discussion of various analysis options for cultural heritage materials.

This visit was very beneficial and raised new collaboration possibilities in the future.