“This comprehensive review brings together technical depth and years of personal lab experience, shaped by long hours at the bench, countless peer discussions, and valuable lessons learned along the way. It offers a detailed, practice-oriented guide to how derivatization can dramatically improve analyte retention and ionization in LC-MS, especially for challenging amino compounds. The article dives into reagent selection, method optimization, and real-world troubleshooting – tools I wish I’d had starting out.”
This work was supported by the Estonian Research Council grant PUT1589, and by the Estonian Ministry of Education and Research (TK210). The research was conducted using the Estonian Center of Analytical Chemistry, funded by the Estonian Research Council (TT4).
Our group’s journey into catalytic studies began years ago. In the first period our main activity was measuring the pKa values of Brønsted acids catalysts and relating them with catalytic activity. However, it was always problematic that the catalytic activity was quantified by different authors in very different ways: different reactions, different substrates of the same reaction, different ways to express activity (rate constant, yield), different solvents, different concentrations, different temperatures… All this diversity makes comparing catalytic activity difficult to impossible.
So, we set forth to find a model reaction, define conditions and a unified quantitative parameter for expressing acatlytic activityof various Brønsted acid catalysts.
This endeavour has now reached its first result: PhD student gleb Maksimov from our group discovered that the transfer hydrogenation reaction with substituted quinoline has the suitable characteristics for this work and utilizing the Kimball-Collins theory modelling approach applied to rate constante (measured by NMR), a catalytic activity parameter was defined that enables unified and comparable quantification of the catalytic activity of Brønsted acids! The proof of principle is now published: Molecular Catalysis2025, 573, 114846. Towards quantifying catalytic activity of homogeneous Brønsted acid catalysts.
Congratulatuons, Gleb!
However, this work is far from complete. Gleb together with new students will continue to improving te methodolog and widening the applicability of the approach so that many more results and with higher quantitative accuracy would be possible in the future. We are excited about the potential advancements and look forward to sharing more updates as the research progresses.
(This research was supported by grant PRG690 from the Estonian Research Council)
Within the framework of the PRG1198 research project Dr Signe Vahur with her team (Dr Anu Teearu, Dr Rünno Lõhmus, Martin Leissoo, Dr Alexey Treshchalov, Dr Janis Lungevics, Dr Georg Arju, Dr Hilkka Hiiop) has published a new article titled “Characterisation of laser-ablated craters of different painting materials and evaluation with modified LA-APCI-MS system” in the Journal of Talanta. The article is available here: https://doi.org/10.1016/j.talanta.2025.127856
The article presents preliminary results obtained by investigating the pulsed 355 nm Nd:YAG laser’s impact on specific painting materials (oil and acrylic paints and varnish) surfaces by characterising the area and volume of laser-ablated craters (measured with an optical microscope and 3D profilometer) obtained with different laser energies and the number of pulses at 90°, 70°, and 45° incidence angles and evaluating intensity of corresponding MS signals obtained with APCI-MS.
For the first time, potentiometric pH measurement traceable to the conventional aqueous pH scale has been successfully demonstrated in a low-polarity solvent, 1,2-dichloroethane (1,2-DCE)!
Paulo and Jaan from our group achieved this remarkable result, which has now been published: “Experimental Unified pH Scale in 1,2-Dichloroethane” (Phys. Chem. Chem. Phys., 2025, 27, 3810–3816).
The measurement approach is rooted in the unified pH scale (pHabs scale) concept and is based on pairwise differential potentiometric comparisons of solutions yielding their pHabs differences (ΔpHabs values). 85 such pair-wise measurement comparisons were carried out between solutions prepared in 1,2-DCE, some solutions in mixed solvents and aqueous standard pH buffer solutions. The resulting pHabs “ladder” is pictured in Figure 1.
Figure 1. pHabs scale of solutions in 1,2-DCE, linked to the standard aqueous buffer solutions and comparison against reported pHabs values in the literature.
Applying a least squares minimization approach to the ΔpHabs values and taking into account the reference values of the aqueous standard buffers allowed us to assign pHabs values to 19 equimolar buffer solutions in 1,2-DCE, yielding a pHabs range of −2.9 to 11.0. The consistency standard deviation of 0.17 pH units—higher than similar measurements in polar solvents—reflects the experimental challenges of working in low-polarity media.
Multiple salt bridge configurations (shown in Figure 2) were tested to improve measurement stability. Out of the four tested configurations, a separate salt bridge configuration (SB4) with PEEK capillary tubes yielded the most stable and reliable results, extending measurements for up to five hours without significant drift.
Figure 2. Different salt bridge setup configurations used in the work.
Direct pH measurement of 1,2-DCE solutions against standard aqueous pH buffers is challenging because of the very different nature of the solvents and possible water contamination of 1,2-DCE can significantly affect the measurements. Therefore, bridging solutions (a 60:40 acetonitrile/pH 4 formate solution and buffered ethanol) were employed to facilitate measurements against standard aqueous pH buffers. This approach allows the pHabs values in 1,2-DCE to be directly comparable to the aqueous pH values.
The obtained results confirm that potentiometric pHabs measurements are possible in low-polarity solvents, paving the way for experimentally linking many low-polarity solvents into a unified pH scale. Employing pHabs to compare solution acidity across different media will improve our understanding of how pH impacts processes in catalysis, liquid chromatography, sustainable energy, and the interpretation of acid-base processes in various solvents.
(This research was supported by grant PRG690 from the Estonian Research Council)
We’re delighted to share that members of our Archemy and Analysis of Cultural Heritage Objects groups have published a new article titled, “Influence of Mineral Composition and Firing Temperature on the Micro- and Mesoporosity of Replicate Archaeological Ceramics” in the journal of Clays and Clay Minerals (Volume 72, 2024, e13). Read the Open Access article here.
This study examines how the mineral composition of clay and temper, along with firing temperatures, influences the formation of micro- and mesopores in pottery. The porosity of ceramics is considered a significant factor in the absorption and preservation of organic compounds, such as lipids, within archaeological pottery. Our research provides the first quantitative analysis of pore structures in ceramics designed to replicate archaeological samples, establishing valuable baseline information for future investigations into ceramic porosity and organic residue analysis.
We are excited to share our latest publication titled, “pKaH values and θH angles of phosphanes to predict their electronic and steric parameters” (Dalton Trans., 2024, 53, 14226-14236. https://dx.doi.org/10.1039/d4dt01430h).
In this study, we delve into the fascinating world of phosphanes – a versatile class of organic bases that play a crucial role in a wide array of chemical applications. Phosphanes are known for their incredibly diverse range of basicities, with pKaH values spanning over 30 orders of magnitude. One of the key insights from our research is that pKaH values can be a valuable alternative to Tolman electronic parameters (TEP values) for assessing the electronic properties of phosphanes. This finding opens up new possibilities for researchers to evaluate phosphanes without the need for the time-consuming preparation or calculation of metal-ligand complexes.
In addition to electronic properties, we also propose new geometric parameters to assess the steric properties of phosphanes – the θH angles, which have the advantage of being accessible by simple computations. Together, the pKa values and θH angles provide a straightforward approach to understand and predict the behavior of phosphanes in various chemical environments and processes.
Our study combines computational and experimental findings to offer a fresh perspective on how phosphanes can be analyzed and utilized, and we believe it will be a valuable resource for researchers working with these compounds. We invite you to read the full article to explore the detailed findings and implications of our work.
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.
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
In this work, a new group of bases with benzophenoneiminyl (bpi) moiety was synthesized and characterized. A convenient one-pot approach was employed to synthesize the starting compound tris(benzophenoneimino)phosphane (P(bpi)3): benzophenone imine was deprotonated using MeMgCl, followed by its reaction with PBr3 in diglyme. This method offers an alternative for preparing other (amino)phosphanes as well when lithio-intermediates and/or protonated phosphanes are not viable options. P(bpi)3 was subsequently utilized to synthesize a variety of related phosphonium cations and phosphazenes.
Crystals from synthesis
The stability of the resulting phosphonium ylides was assessed through their deprotonation. In certain cases, the bulky substances demonstrated the ability to form P-N heterocycles with adjacent P and N atoms and P=C double bonds which are quite rare and only some representatives of this type of heterocycles have been reported before. The basicities of benzophenone imine, P(bpi)3, phosphonium ylides, and phosphazenes were evaluated experimentally (in MeCN) or computationally (in MeCN, THF, and gas-phase). Additionally, representative X-ray crystallography (XRD) structures were presented and discussed. Although the bpi-compounds are not as strong as many existing bases, they still exhibit considerable basicity and could be employed as reagents to overcome common challenges such as solubility, ion-pairing, lack of UV-Vis properties, and other issues.
In this study, multidimensional front-face fluorescence spectroscopy measured from surfaces using a fiber optic probe was assessed as a non-invasive and non-destructive method for the analysis of components in natural textile dyes. Multidimensional fluorescence data was acquired for a collection of wool yarns dyed with natural dyes (31 dyed wool yarn samples that were self-dyed with 18 different natural dyes) that were used as references in a case study of two historical textiles for which liquid chromatography-mass spectrometry was used as a confirmatory technique.
Self-dyed reference yarnsSelection of characteristic EEMs of self-dyed reference samples
Natural dyes are multicomponent mixtures and can originate from different sources (e.g., plants, insects, and fungi). Due to their complex chemical composition and the inherent lability (photooxidative fading and bleaching), the analysis of natural dyes can be quite challenging and in order to analyze dyes on textiles, it is often best to combine different analytical methods. However, for the analysis of dyes, common and often the most informative methods, like chromatographic separations coupled with different detectors, are all invasive/destructive. The aim of this work was to explore the potential and limitations of fluorescence spectroscopy in analyzing natural dyes from dyed wool yarns using EEMs (excitation-emission matrices), measured directly from the surface of the objects, non-destructively and without any sample preparation.
To demonstrate the utility of the fluorescence method, analysis was conducted on two case study samples – fibers from historical artifacts. Comparing the EEMs of the reference yarns with our unknown case study samples, we were able to identify that dye from a plant of the Rubiaceae family (bedstraws and madders) was used for dyeing the case study samples.
Here you can find the 50-day free access to the article.
One of the case study objects; Tapestry “Solomon is receiving a bride. Solomon Court” (year of production 1547); Textile sample was obtained from the Conservation and Digitization Centre Kanut (Estonia).
