Our group is well-known for pKa measurements in different solvents. So far, mostly UV-Vis spectrophotometric method has been used. Recently Elisabeth Parman (on the photo) from our group has been developing a method for measuring pKa values of fluorocompounds, using 19F NMR. NMR measurements to determine pKa values have several advantages compared to UV-Vis spectrophotometry. For example, accurate concentrations are not needed, the method is much more tolerant to impurities and several compounds can be measured simultaneously. The newly developed method has now been published in the Journal of Physical Organic Chemistry: Determination of pKa values of fluorocompounds in water using 19F NMR by E. Parman, L. Toom, S. Selberg and I. Leito.
In this work, the developed method was applied to 19 fluorocompounds – fluorinated phenols, carboxylic acids and sulfonamides, hexafluoroisopropanol (HFIP), perfluoropinacol, etc – with the aim of determining their pKa values in water, in the range from about 3.5 to 10. Several advantages of the 19F NMR method were demonstrated in pKa measurement. In particular, using multiple relative measurements against several reference compounds with known acidities it is possible to obtain highly reliable pKa values. Elisabeth convincingly demonstrated that the literature pKa values of two of the investigated compounds were inaccurate and provided more reliable values for them.
New type of pKa – biphasic pKa in octanol water system
It is not frequent that a new quantitative measure of some physicochemical characteristic is introduced. Recently our group managed to do exactly that by introducing a novel approach – termed as biphasic pKa values – of measuring the acidity/basicity of lipophilic compounds embedded in water-immiscible media (membranes or solutions) at equilibrium with aqueous solution.
In this approach, the H+ ion activity is determined in the aqueous phase, while the concentration ratio of protonated and deprotonated forms of acid/base is measured in the lipophilic phase with any suitable technique. The approach has been demonstrated on the example of biphasic pKa values of some lipophilic indicator bases in the octanol: water system, measured using UV-Vis spectrophotometry. The counterion identity and concentration, as well as the overall ionic strength in the aqueous phase, are included in the standard state definition.
This work has been published S. Selberg, S. Tshepelevitsh, I. Leito Croat. Chem. Acta 2018, 91, (4) and will form a part of the PhD thesis of Sigrid Selberg.
Biphasic pKa values are envisaged to be useful for characterizing lipophilic indicators, synthetic receptors, phase transfer catalysts and other implements that are used in hydrophobic media (e.g. in sensor membranes) in contact with water.
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.
(On photo: Sigrid Selberg)
Eurachem 2019 workshop: Validation of targeted and non-targeted methods of analysis
Our group is proud to be the leading organiser of the 2019 Eurachem General Assembly and the accompanying scientific workshop “Validation of targeted and non-targeted methods of analysis”!
The Workshop will take place in Tartu (Dorpat conference centre) on May 20th and 21st. The programme of the workshop, as well as registration and abstract submission are available at the event website:
https://eurachem2019.akki.ut.ee/
The workshop addresses the current status of analytical method validation in general and specifically validation of the non-targeted methods (i.e. ones where the analyte is not defined beforehand). Non-targeted methods are an especially noteworthy part of the workshop programme, because their validation involves specific issues (since analyte is not known it is not possible to make validation experiments with it) and is significantly less developed than validation of targeted methods (i.e. the “normal” analytical methods, where the analyte is known beforehand). At the same time non-targeted methods are becoming increasingly important in environmental protection, food safety, different omics areas, etc.
Some example topics of the workshop are: Validation of targeted methods: where are we? Validation of non-targeted methods – differences from targeted methods. Detection of a multitude of (unknown) components in complex samples: criteria for identification. Managing the huge amounts of complex data from non-targeted methods. Software solutions for validation.
Compact overview of the workshop can be found in the 2nd circular.
These events mark the 30th anniversary of Eurachem and are jointly organized by Eurachem and ECAC (University of Tartu, Tallinn University of Technology and the Estonian Environmental Research Centre).
We are hoping to see many of you in Tartu in May!
Optimization of flow splitting and make‐up flow conditions in liquid chromatography/electrospray ionization mass spectrometry
Recently a study in Rapid Communications in Mass Spectrometry was published. In this study, we optimized the actual split ratio and make-up flow composition in LC/ESI/MS analysis to increase the signal in radio detector and enhance the sensitivity of electrospray ionization.
High methanol content increases electrospray ionization efficiency
We studied make-up flow composition with a set of 20 pharmaceuticals covering 21 different make-up flow compositions. We studied methanol, acetonitrile, isopropanol and acetone as organic modifiers. As we studied positive mode the acidic additives under investigation were formic acid, oxalic acid and propionic acid. DMSO and sulfolane as additives were studied as well. The Methanol/10 mM formic acid in water (90/10) proved to be the best make‐up flow composition in relation to the average sensitivity obtained. Stronger acidic conditions using oxalic acid or higher formic acid concentrations had a clear positive effect on the sensitivity of compounds with low ionization efficiency.
Split-ratios remain stable over main part of the gradient
The second part of this study was testing and monitoring different split ratios (1:10, 1:100 and 1:250) with different splitters (Alliance flow‐splitter kit and homemade T-piece splitter). To monitor the actual split ratio haloperidol solution was added with infusion pump post-column while a haloperidol-d4 solution was added as a make‐up flow by the ISM pump after the splitter. The tested split ratios were relatively stable over the main part of the gradient but showed some variation at very low and very high organic conditions. Differences were larger with methanol compared with acetonitrile containing solvent compositions and when applied without a column or with very long connecting tubing.
I thank Janssen Pharmaceutica and especially Dr Filip Cuyckens for the internship position for letting to gain experience in an industry setting and study these effects. Additionally, I thank Erasmus+ mobility and Smart specialization doctoral stipend for funding my stay.
IRUG 13 Conference on 5-7 December in Sydney, Australia
13th biennial conference of Infrared & Raman User Group, shortly IRUG, was for the first time ever held in Sydney, Australia in a beautiful Art Gallery of New South Wales. IRUG conferences are gathering people using IR and Raman spectroscopy for the analysis of cultural heritage, architecture, and forensic materials. This year 101 people were attending, including Dr Signe Vahur and PhD student Pilleriin Peets from our group. Pilleriin was also introducing her results in analyzing textile fibres with IR spectroscopy in an oral presentation. Development of methods for the analysis of various textiles using ATR- and reflectance FT-IR spectroscopy turned out to be very relevant: throughout all three days, many people approached to discuss the topic, ask questions and advice or to make contacts for later cooperation. We were also very glad that conference participants were interested in our ATR-FT-IR spectral database of cultural heritage and conservation materials, available here.
Three days were filled with a wide range of interesting presentations from analysis of Aboriginal Australian pigments and identification of contents from the coffin of a 2500-year-old Egyptian mummy Mer-Neith-it-es to investigations of cultural heritage materials using neutron techniques. Besides the analysis of traditional pigments, organic pigments, especially synthetic organic pigments and their use in art were discussed (oral presentation by Dr Suzanne Lomax and Dr Steven Saverwyns). Another very interesting and thought-provoking presentation was done by Dr Gregory Smith from Indianapolis Museum of Art. He discussed the difficulties in getting accurate standard reference materials in the field of cultural heritage analysis. His results showing how many false materials can be found on the market (and not only vendors like Kremer Pigmente, but also providers like Sigma Aldrich) were very surprising.
All in all, IRUG 13 conference offered three full days of interesting presentations, a lot of knowledge and useful tips for further research and a pleasant atmosphere with excellent company.
Comparing Electrospray Ionization Efficiencies of Derivatized and Non-Derivatized compounds
Main concern while measuring ionization efficiency (IE) of derivatized compounds is that derivatized compounds are in complex mixtures. To overcome this problem, we developed a chromatographic method to separate these compounds and measure their ionization efficiencies.
If ionization efficiencies of derivatized compounds are measured without chromatographic separation in a complex mixture, which includes analytes, derivatization reagents and different by-products, then matrix effects could occur. This problem can be solved if we first separate these compounds from each other and then measure ionization efficiencies.
Chromatographic method
To separate different compounds, we used a simple chromatographic gradient elution method. One might think, that if compounds have different retention time, then they also elute at different organic phase percentages which obviously affects measured ionization efficiency values. The effect is not so significant, but we could manage to model it and take it into account to level all newly measured ionization efficiency values to a previously measured scale.
logIE measurements
We carried out ionization efficiency measurements with liquid chromatography electrospray ionization mass spectrometry (LC/ESI/MS) and constructed IE scales with a calibration curve for compounds with and without derivatization reagent diethyl ethoxymethylenemalonate (DEEMM). Additionally, we investigated eluent composition effects on ionization. Measured compounds were mainly amino acids but also included some biogenic amines.
Results
We saw, that
- Derivatization increases IE for most of the compounds (by an average of 0.9 and up to 2 – 2.5 logIE units) and derivatized compounds have more similar logIE values than their underivatized variants.
- Measurement of derivatized compounds is possible from the mixture when using chromatographic separation technique.
- It was also noted, that using chromatographic separation instead of flow injection mode tends to slightly increase ionization efficiency.
We managed to link all our results with existing ionization efficiency scale and therefore widen the scale and get comparable logIE values for measured derivatized compounds.
More information could be found in an article published recently at Journal of Mass Spectrometry.
EACH programme at the Sample Treatment 2018 Conference!
On Dec 3, 2018, Ivo Leito gave a presentation at the Sample Treatment 2018 conference (Caparica, Portugal) about the Excellence in Analytical Chemistry (EACH) Erasmus Mundus master’s programme that is coordinated by our group.
The focus of the talk was sample preparation and how is it included in the EACH programme. A key feature of the presentation was a question to the participants as for what else could/should the EACH programme contain in terms of sample preparation, especially keeping in mind emerging techniques. Another one was a call to come to teach at EACH as visiting scholar. During the subsequent coffee breaks a number of people approached Ivo and interesting ideas were proposed as to what to include into the programme’s set of covered sample preparation approaches (dialysis, different microextraction techniques, sonication, etc). Several people also expressed interest to contribute to the programme as visiting scholars.
Call of applications to the EACH visiting scholar scheme is constantly open at the EACH Visiting scholars page and submitting of application is non-binding, so it is encouraged also if you are not yet sure whether you will come.
We are thankful to all participants for their feedback and ideas!
Group seminar at Pühajärve
From 24th to 25th of November our group had a traditional biannual seminar in Pühajärve Spa hotel. The seminar is a nice opportunity to learn about what the group members are doing and which challenges they are tackling. The presentations covered a broad domain of analytical chemistry from fundamental acid-base studies to bioanalyses and analyses of cultural heritage.
Ambient ionization and fluoroalcohols to improve bioanalysis
The first session was focusing on the bioanalytics. Max, a PhD fellow doing an internship in London right now, presented the results of drug analyses from a music festival. Next to strongly varying drug dose, the problem is the strongly varying dissolution of corresponding dose. Next two presentations presented by Rūta, a PhD fellow, and Krit, her undergraduate student introduced fluoroalcohols as novel LC eluent additives and their effect on retention mechanism and electrospray sensitivity. It was really interesting how strongly and unexpectedly differently some fluoroalcohols may change the retention mechanism.
The reliability of fluorescence measurement
The second session focused on acid-base and coordination chemistry. Alo, a PhD fellow, presented his improvements and challenges in the synthesis of bambusuril derivatives. Elisabeth, a master student, introduced 19F NMR measurements of pKa of fluorinated compounds in acetonitrile. Sigrid, a PhD fellow, gave a lecture on how to measure correct fluorescence spectra accounting all effects that may affect the spectra. She showed the importance of concentration and the inner filter effects correction on fluorescence spectrum. Andre, a PhD fellow, wrapped up the seminar with the presentation of his results in gas phase acidity measurements.
Did I get real cashmere scarf from the market?
The third session was focusing on the analysis of cultural heritage. Eliise, a PhD fellow, presented the comparison of four most applied derivatization procedures for analysis of binders in GC. Pilleriin, a PhD fellow, presented her results of textile analyses and a model developed to classify unknown textiles using ATR-FT-IR spectroscopy. Markus, a master student, presented his work on coupling LC with nano-ESI FT-ICR-MS. Juhan, an undergraduate student, introduced his work on acid-base measurements of fluorophoric pH sensor molecules.
After inspiring presentation and fruitful discussions, we had a nice opportunity to relax in the spa and sauna. Additionally, group members discussed with Prof. Leito and Associate Prof. Herodes the SR-15 report from IPCC.
Is open science in terms of metadata really possible?
Next day was kicked off by Astrid, a PhD fellow, who compared the measurement of binding constants using isothermal calorimetry and NMR. Next, Piia, a PhD fellow, introduced her results on using the data from the literature to test, validate and improve the electrospray ionization efficiency prediction model. The take-home message from Piia’s presentation was the need for data integrity on results one is reporting and clear explanations on how one obtained these results. Additionally, a machine-readable format of the structure is a great help to simplify data mining from literature. Next, Jaanus, a PhD fellow introduced the results from a collaboration with a visiting PhD fellow Tingting Wang from DTU, Denmark. He showed the results of standard substance free quantification in the example of pesticides in food matrices. Ernesto, a PhD fellow, introduced his doctoral project on designing and describing the anionic derivatization reagents in LC/MS.
What’s causing this smell?
The second day was wrapped up by Associate Prof. Koit Herodes. He showed us a case study on the analysis of smell of ruined goods. Finally, he presented the current edition of validation software our group is developing to simplify and automate the validation in LC/MS analyses.
Thanks to all participants for interesting and inspiring presentation and for fruitful discussions.
The biggest development of the SI system in decades!
Today, On Nov 16, 2018 the General Conference on Weights and Measures (CGPM) unanimously decided to fundamentally remake the SI system of measurement units. Perhaps the most important change is that the kilogram will not be defined via a physical artefact – the platinum-iridium cylinder – but in terms of the Planck constant. As a result, for the first time the entire SI system will be defined entirely on the basis of fundamental constants, which has been the aim for decades!
The change will become effective on the 2019 World metrology day – May 20, 2019.
More information can be found in the post CGPM votes unanimously to change the SI by Dr Steve Ellison at the Eurachem website.
(Image: Wikipedia)
UnipHied EMPIR Network at Baltic Electrochemistry Conference 2018
On Nov 05, 2018 Ivo Leito gave a presentation Unified pH about the pan-European research network of fundamental pH Research UnipHied (www.uniphied.eu) at the 7th Baltic Electrochemistry Conference organized by the University of Tartu.
The presentation started with explaining the need for the experimental realization and measurement capability of unified pH (pHabs). Thereafter the current state of art of measuring pHabs values was described and finally, some first exemplary results were highlighted.
The presentation created a lot of interest from the participants and roughly as many questions were asked as for the other four presentations of the same session put together!
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 chromatography, etc.
The central aim of the UnipHied network is to establish at international level measurement capability of pHabs values that would be applicable also at routine laboratory level. The two key activities for achieving that are creating a reliable method for the experimental or computational evaluation of the liquid junction potential and between aqueous and non-aqueous solutions and developing 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 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, initiator).
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.