New Open Access publication: GC-MS analysis of aged oil paints

Our group recently published a new Open Access research article – Quantitative GC-MS Analysis of Artificially Aged Paints with Variable Pigment and Linseed Oil Ratios, Molecules 2021, 26 (8), 2218. 

In this freely accessible publication, seven sets of artificially aged paints prepared from a pigment (chrome oxide green, natural cinnabar, Prussian blue, red ochre, hematite + kaolinite, zinc white, or yellow ochre) and linseed oil were analysed with GC-MS. One of the main aims was to study if the pigment concentration in the paint samples affects the drying of the linseed oil. 

The palmitic acid to stearic acid ratio (P/S), azelaic acid to palmitic acid (A/P), and the relative content of dicarboxylic acids (∑D) showed, that besides the type of the pigment, also the concentration of the pigment can influence these values that are commonly used to identify the type of the oil or to characterize how dried is the sample. 

The absolute quantification of stearic acid (see figure on the right) showed that the drying of all paint sets (except for zinc white) were influenced by the pigment concentration. Therefore, this is another factor that needs to be taken into account when studying aged oil paints. 

 

 

Aminoacridines as matrix materials for the analysis of complex samples in MALDI(-)-MS

A highly interdisciplinary study ranging from computational chemistry to cultural heritage has now been published – Experimental and Computational Study of Aminoacridines as MALDI(-)-MS Matrix Materials for the Analysis of Complex Samples, J. Am. Soc. Mass Spectrom. 2021.  

9-aminoacridine (9-AA) is a well-known matrix material used for the MALD(-)-MS analysis. Among the other monoaminoacridines (AAs), only 3-AA has been tested once (in our cultural heritage workgroup) but the suitability of the other AAs was unknown.

To fill this gap, the capabilities of all five AAs were studied by analysing different materials (stearic acid, colophony resin, dyer’s madder, and a resinous sample from a 16th-century shipwreck). Also, a vast range of properties for these aminoacridines were experimentally or computationally characterized (including UV-Vis absorption and fluorescence spectra, proton transfer reactions, crystallization). 

The results demonstrated, that all the AAs are suitable for the MALDI(-)-MS analysis of these materials. Interestingly, 3-AA and 4-AA outperformed the other AAs (including the best-known 9-AA) and were the preferred matrices for the analysis of samples studied in this work.   

 

 

Acidity scale in acetonitrile: 231 pKa values spanning 30 orders of magnitude

The equilibrium acidity scale (pKa scale) in acetonitrile (MeCN) has been supplemented by numerous new compounds and new ΔpKa measurements and has been published in Eur. J. Org. Chem. 2021, 1407–1419 (Open access). The pKa scale now contains altogether 231 acids – over twice more than published previously – linked by 566 ΔpKa measurements and spans between the pKa values of hydrogen iodide (2.8) and indole (32.57), covering close to 30 orders of magnitude. The acids have wide structural variety, ranging from common families – phenols (e.g. picric acid, alizarin, polyhalogenophenols), carboxylic acids (e.g. acetic, benzoic, retinoic and sorbic acid), sulfonic acids, hydrogen halides) to highly special molecules (chiral BINOL catalysts, bis(benzoxazole-2-yl)methanes, polyfluorinated compounds) and superacids (fluorinated sulfonimides, cyanoform, tetracyanopropenes).

Measurement results acquired over the last 15 years were added to the scale and new least squares treatment was carried out. The treatment yielded revised pKa values for the compounds published previously, with the root mean square difference between revised and previous values 0.04, demonstrating very good stability of the scale.

Correlation equations were developed for estimating pKa values for the studied types of compounds in water, DMSO, DMF and 1,2-dichloroethane on the basis of pKa values in acetonitrile. These equations enable predicting pKa values with an average error around or less than 1 pKa unit, which is a sufficient accuracy for many applications.

The scale is expected to be a useful tool for the widest possible research areas in organic chemistry, electrochemical power sources, catalysis, etc.

Design, synthesis and application of carbazole macrocycles in anion sensors

Our supramolecular analytical chemistry team has published an article (Beilstein J. Org. Chem. 2020, 16, 1901-1914) about developing carboxylate sensor prototypes that use macrocyclic carbazole receptors as ionophores.

Usually, reported research concludes with the demonstration of binding abilities of receptors and only suggests possible applications at a theoretical level. This work stands out from most publications by incorporating the entire workflow from receptor design to the characterisation of working sensor prototypes.

By involving this additional step, the team demonstrated the shortcoming of evaluating binding with just the receptor and analyte in solution. The predictions of selectivity can change considerably when measuring binding in an actual sensor membrane. This does not mean that such binding measurements would be obsolete, as the issue of binding anions selectively remains relevant in supramolecular chemistry.

The work was published in collaboration with the group of prof. Johan Bobacka at Åbo Akademi. The open access article was published in the Beilstein Journal of Chemistry thematic issue “Molecular Recognition” (in memory of Prof. Carsten Schmuck).

Symmetric Potentiometric Cells for the Measurement of Unified pH Values

Recently the UnipHied consortium published a new article – Symmetric Potentiometric Cells for the Measurement of Unified pH Values. Symmetry 2020, 12, 1150, where we compared the performance of different cells and instruments used to measure acidities on the unified pH scale (pHabs). The advantage of the unified pH scale is that it enables expressing the acidities of any systems – non-aqueous, solutions, colloidal systems, etc – via pHabsH2O values, which are directly comparable to the conventional pH values of the aqueous pH scale.

This is the first time unified acidities have been measured outside of our group. Nine partners from Europe – national metrology institutes and universities – have set up systems to measure pHabs and validated them with standard aqueous buffers.

The results show that the method is robust and does not depend on the cell nor the instrument (pH meter, potentiostat, or electrometer). The inherent symmetry of the cell design helps to reduce the experimental workload and improve the accuracy of the obtained results.

The next step is to measure unified acidities of non-aqueous systems, which could be used by routine laboratories to calibrate their pH electrodes.

The UnipHied project 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.

The secrets of two mummies have been unravelled

PLOS ONE has recently published a multidisciplinary paper on two Egyptian child mummies lead and participated by the members of our group. The team of 19 experts unravelled the secrets of two Graeco-Roman child mummies by applying most recent analytical techniques from archaeology, forensic sciences, analytical chemistry, medicine, entomology, and genetics. This is one of the most extensive multidisciplinary study of ancient mummies and the paper is free to download here.

New non-invasive approach to analyze textile fibers

Another new method development in our group has been assembled into a publication. Article by Pilleriin Peets (on the picture), Karl Kaupmees,  Signe Vahur, and Ivo Leito in the journal of Heritage Science introduces non-invasive approach to identify all kinds of different textile fibers using reflectance-FT-IR spectroscopy and chemometry. In this work 61 single-component textile pieces were analyzed, 4000 spectra were recorded and all in all 16 different textile fiber types were characterized. As reflectance-FT-IR spectroscopy is not widely used to analyze samples with an uneven surface, in our best knowledge, this article provides the largest collection of r-FT-IR spectra from textile fibers that is recorded and published. All the r-FT-IR spectra from different fiber classes are now available for other scientists, conservators, museum workers and industries to use!

PCA classification graph of different textile fiber classes. Peets, P., Kaupmees, K., Vahur, S., Leito, I. Reflectance FT-IR spectroscopy as a viable option for textile fiber identification. Herit Sci  7, 93 (2019)

New publication – retention studies in C18 column using novel fluorinated eluent additives

It is essential to understand the interaction between the analyte, mobile phase and the column chemistry for the best possible separation of molecules. Of all three, the mobile phase in HPLC is the easiest to modify and thus, usually contains different eluent additives or buffers. While using mass spectrometry undoubtedly increases the variety of analytes possible to detect, it also introduces limiting factors such as the requirement of the volatility of the eluent. Most common additives in LC-MS systems are formic and acetic acid, their ammonium salts as well as ammonium bicarbonate. In our recent paper, we have proposed novel – fluorinated, eluent additives (hexafluoroisopropanol, hexafluoro-tert-butyl alcohol, trifluoroethanol as well as nonafluoro-tert-butyl alcohol and perfluoropinacol).  Their influence was shown on rather simple exemplary molecules, which are widely spread over different logP values, containing protonated and deprotonated acids and bases. All novel fluorinated eluent additives demonstrated a strong influence on basic polar analytes in basic medium – they drastically increased retention. A decrease in retention was observed for acidic analytes when these novel eluent additives were used.

Moreover, current research displays a comprehensive overview of retention mechanisms for nonafluoro-tert-butyl alcohol and is the first time ever when perfluoropinacol has been introduced as eluent additive for reversed phase chromatography. Additionally, the influence on MS signal was studied when fluoroalcohols were used as eluent additives. This is also the first time when the absolute pH (pHabs) scale was used for expressing the mobile phase pH.

Current fundamental research forms a basis for a better understanding of the influence of fluoroalcohols as eluent additives and will help in the assay development in a wide range of applications.

This work is part of a larger endeavor – to promote a wider usage the unified pH scale (pHabs) by the research and technology communities, which is currently in progress via the UnipHied.

The UnipHied project 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.

 

 

New publication – Instrumental techniques in the analysis of natural red textile dyes

A wide variety of different dyes, complex composition of natural dye sources and low concentrations in samples make the identification of textile dyes challenging. In our cultural heritage group, work has been done for years to overcome some of these problems. Using seven different red dye sources and five instrumental approaches, a method for the analysis of textile dyes has now been developed in our lab to study different archaeological findings, museum artifacts, and other textile pieces. More about the results can be found in the article published in the Journal of Cultural Heritage by P. Peets, S. Vahur, A. Kruve, T. Haljasorg, K. Herodes, T. Pagano and I. Leito.

The usefulness of this developed method has been proved by analyzing several case-study samples from Estonian National Museum, KANUT, and private collections. Thanks to the multiple instrument combination and especially the usage of high-resolution mass-spectrometry, it was also possible to identify synthetic organic dyes without the use of any standard substances.

EACH is featured in Analytical and Bioanalytical Chemistry!

The educational section of the leading analytical chemistry journal Analytical and Bioanalytical Chemistry, the ABCs of Education and Professional Development in Analytical Science has published a paper about the EACH programme: EACH (Excellence in Analytical Chemistry), an Erasmus Mundus Joint Programme: progress and success

The EACH programme is an Erasmus Mundus Joint Master Degree programme coordinated by our group. It has become one of the leading master’s degree programmes focusing on analytical chemistry within its short existence. The programme is run in cooperation by four top European universities: in addition to the coordinating university, the University of Tartu (first-year university), also Uppsala University (Sweden), Åbo Akademi University (Finland) and University Claude Bernard Lyon 1 (France) are involved as second-year and specialisation institutions.

The paper gives a comprehensive overview about the EACH programme, including a detailed overview of what EACH is, what kind of topics are taught during the first study-year at the University of Tartu, what is the nature of the different study-tracks (specialisation during second study-year either in Sweden, Finland or France), what extra activities, such as internship and winter school the EACH programme offers. The paper also gives an explanation on why it is necessary to have such a programme like EACH, and how to be a part of the EACH experience.

One section in the paper is dedicated to the impact of the EACH programme – with the four years that the programme has accepted students, it has reached a lot of countries and the employability rate of the graduates is almost 90%.

This Autumn, the fifth intake of EACH students is starting their studies at the University of Tartu, expanding the blue areas on the map presented above even more.

For more information on the EACH programme, please see the programme’s webpage and also the newly published paper.