Every year Estonian University of Life Sciences organises a conference called “Healthy animal and healthy food” where Dr. Riin Rebane made a presentation “Fight against food fraud” which explained the ever-expanding role of analytical chemists in food science. Reasons for food fraud vary, but are almost always for monetary gain and therefore food fraud is in constant progress. One good example is honey analysis, where for decades there has been a change in methods in order to identify whether honey is real or whether it is identified with correct botanical or geographical origin. As a natural product, no two honeys are identical and this makes identification further more challenging for the chemists. One of the possible methods is amino acid analysis since the amino acid content can be like a fingerprint for honeys and in University of Tartu we have analysed few hundreds of Estonian honeys and have seen that that foreign honeys do differ in most cases and also that there is a correlation between the amino acid content and botanical origin. But nevertheless, even this method might not work every time and chemists are looking towards methods such as nuclear magnetic resonance spectroscopy and even DNA-analysis to get better certainty for determining the origin of honey.
The summary based on the presentation was also reported in the newspaper Maaleht.
Dr. Anneli Kruve, a leader of research team focussing on ionization efficiency studies in electrospray, is currently a Humboldt fellow in Freie Universität Berlin and visited the 1st European Mass Spectrometry Conference in Saarbrücken (Germany) this month. She describes some of the highlights of this conference in her blog, you can read the post below.
Last week I had a chance to take part in the European Mass Spectrometry Conference that was hosted by DGMS (German Society for Mass Spectrometry) and SFSM (French Society for Mass Spectrometry). Below I share a few key ideas from this nice conference that took place in Saarbrücken over 5 days.
The conference was opened with a plenary lecture by Prof. Alain van Dorsselaer who summarized the main work he and his group has done on mass spec during the last 30 years. One of the key ideas, that came up several times in his talk referred to the fact that endless possibilities are accompanied by extreme data load. The amount of data in LC/MS/MS is huge and it is very complicated to analyse these massive data sets. Several other scientists, including Prof. Andreas Roempp and his group, also stressed the importance of transparent and open source data analyses and storage that could eventually simplify the data treatment. These ideas strongly resonate with my own ideas of applying more data science tools in primary data treatment in mass spectrometry, as today the data processing is by far limiting the progress in several fields of analytical mass spectrometry. Mostly this is the case for fields, where the science is still in the “discovery” stage; meaning that the scientists aim at finding the important compounds and yet do not know which these compounds could be. Such fields include metabolomics, proteomics, environmental science, etc.
Prof. Philippe Schmitt Kopplin stressed the importance of high throughput in metabolic sample analyses and explained why dissolve-and-shoot approach (flow-injection or infusion combined with MS) is often most practical. Also, he showed several case studies where marker compounds could be reliably identified with this simple approach if accompanied with efficient and accurate data processing. A particularly interesting example was a case study of 170-year-old wine from the bottom of the Baltic Sea.
Prof. Carsten Engelhard showed an extremely clever, almost brilliant, method to analyse nanoparticles with simple dilution & infusion experiment. The infusion of homogeneous solution to ICP-MS instrument causes an almost constant signal with small random variations. However, if the solution of nanoparticles is infused to ICP-MS, most of the time there is no signal (only noise). When one of the nanoparticles enters the plasma a signal suddenly occurs causing a peak in the chronogram. The height of the signal reflects the size of the nanoparticle and the number of peaks per volume indicates the concentration of the nanoparticles.
Prof. Thomas Kraemer introduced us to the world of forensic analyses. Particularly, he focused on MALDI imaging techniques, that allow revealing drug intake or exposure to toxic compounds. For this purpose his lab is using two types of samples, the traditional hair and lately also toenails, to overcome the problem arising for hairless people. Interestingly, the single hair analysis also reveals time-resolved information with high precision; therefore, allowing to distinguish between one-time and long time exposures.
You can check out more posts from our team studying ionization efficiencies kruvelab.com
Charged droplets occur everywhere in the world. They are created by the oceans (known as sea spray aerosols), near waterfalls and in thunderstorm clouds. Such droplets are expected to play significant role in environmental processes. Similar droplets are also created in electrospray ionization (ESI) source.
Mari Ojakivi joined Mass Spectrometry lab three years ago to conduct her bachelor thesis with us. Mari started studying how different acids, salts, and bases influence the ionization of some amines in charged water droplets. Soon, some extremely interesting results were revealed that allowed to make much wider conclusions about charged droplets.
It became possible to pinpoint, that protonation of the amines is strongly dependent on the type of additives present in the droplets and is virtually independent of the pH of the solution used for “preparing” the droplets. In “normal” solutions the protonation is determined solely by the pH of the solution. This led us to conclude that some of the additives change something about the droplets that other additives do not affect. It turned out, that the factor determining the protonation is the cation present near the surface of the charged droplets. Cations, such as hydronium ion, which are strong acids protonate the compounds, while weak acids, such as ammonium cation, do not. If both types of cations are present in the solution, the protonation is determined by the ion that has higher affinity for the droplets surface. The support for this model was found from the molecular dynamics simulations carried out in Prof. Konermann’s group.
Why is the protonation in charged droplets at all important? Protonation is one of the fundamental properties of compounds; it may catalyze reactions, break up or induce complexation, change conformation of the macromolecules, etc. Therefore, it can be assumed, that the reactions and processes taking place in charged droplets also depend on the protonation.
Mass spectrometry is currently probably the No 1 technique for determining trace-level components in complex (especially biomed-related) mixtures. The key issues in such applications are sample preparation, sample introduction to MS and ionization of components of interest (analytes). Big efforts are continually made to improve any of them.
In his recent development – Sponge spray – Max Hecht, an AMS graduate, now PhD student at UT attempts improvements in all of the above issues. The elegant approach proposed by Max utilizes a volumetric sampling device – a hydrophilic sponge, which after absorbing a predetermined amount of sample (e.g. blood or urine), can be directly used for sample introduction to MS and ionizing the analytes.
Further developments of this approach may lead e.g. to fast medical diagnosis MS methods that, contrary to the current situation with MS in medicine, could be applied as “bed-side” diagnosis tools in hospitals.
(Photo: Max Hecht working with the sponge spray ion source)
The reception of this talk was one of the warmest during the meeting! Several participants came later to say words of thank for offering such a valuable resource to the LC-MS community. There were also some interesting ideas proposed regarding topics that could be covered in the online course. LC-MS and MiC issues, such as validation, are among core competences of the UT Analytical Chemistry research group. The tutorial review, the on-line course, as well as the ValChrom software together form a nice outcome of joining these competences together.
Concerning the topics of the meeting in general, they were remarkably diverse and not so heavily dominated by biomedical MS as is often the case at mass spectrometry meetings. Interesting presentations were given on gas-phase ion processes, different laser techniques in MS (e.g. for analysis of solids without sample preparation), advanced catalysis studies by MS, LC-ICP-DRC-MS for trace element speciation, the possibility of making a high-end LC-HRMS system an “open access” system within an organization, etc.
Think Negative: Finding the Best Electrospray Ionization/Mass Spectrometry Mode for Your Analyte
Previously our group has developed extensive ionization efficiency scales in ESI positive and negative mode. Thus far, the comparison between the two modes has only been qualitative. Due to use of different anchor compounds the scales were not quantitatively comparable. To solve this problem and to enable direct quantitative comparison of the two ESI modes we searched for an anchor compound ionizing to the similar extent in both modes. To find such a compound we combined mass spectrometry with laser induced fluorescence measurements (to find out the solvent composition and pH in the ESI droplets), NMR and UV-Vis (to characterize the potential anchoring compounds ionization degree in corresponding solvent). Trans-3(3-pyridyl)acrylic acid was found to be a suitable anchoring compound, if analysed in mobile phase with pH 4.00.
The link between two ESI modes ionization efficiency scales enables the user to choose the most optimal ESI mode for analysis for the analyte in question.
We also compared ionization efficiencies of 33 compounds ionizing in both modes and found that, contrary to general practice, negative mode allows higher ionization efficiencies for 46% of the compounds. For 18% positive mode ESI provides better ionization efficiencies and for 36% the results obtained in both modes are comparable. However, not all compounds can be ionized with ESI negative mode, and some unfortunately also not with ESI at all.
Published in: Piia Liigand; Karl Kaupmees; Kristjan Haav; Jaanus Liigand; Ivo Leito; Marion Girod; Rodolphe Antoine; Anneli Kruve; Anal. Chem. DOI: 10.1021/acs.analchem.7b00096
These very important (and up to now not completely solved) questions got a lot clearer on Aug 31, 2016 as PhD dissertations addressing these topics were defended at UT Institute of Chemistry.
Asko Laaniste (left on the photo) in his thesis titled “Comparison and optimisation of novel mass spectrometry ionisation sources” and in the recent paper ESI outcompetes other ion sources in LC-MS trace analysisAnal. Bioanal. Chem. 2019 has carried out an extensive experimental comparison of 4 different LC-MS ion sources operated altogether in 7 different modes in the analysis of 41 different pesticides. The obtained large pool of data was used for comparing the sources in terms of matrix effects, limit of detection (LoD), repeatability, linearity, signal to noise ratio (S/N) and sensitivity.
Asko demonstrated that for low levels of analytes in most cases the conventional ESI is the ion source of choice (provided the analytes are ionizable with ESI), while dopant-assisted APPI is a good alternative if low detection limits are not required and if compounds not ionizable with ESI are determined.
This is currently the most comprehensive comparison of this type available and Asko’s thesis (and the forthcoming publication) could serve as a “desk manual“ for LC-MS practitioners on choosing ion source for LC-MS analysis.
The central question of Hanno Evard’s thesis “Estimating limit of detection for mass spectrometric analysis methods” and in the corresponding two-part tutorial review Tutorial on estimating the limit of detection using LC-MS analysis (Anal. Chim. Acta2016, 942, 23-39, Anal. Chim. Acta2016, 942, 40-49) was: what is the best way of evaluating detection limit (LoD) of an analytical method? There are around ten widespread approaches for LoD in the literature (plus less well known ones) and the LoD values obtained using different approaches can differ by up to 10 times.
Hanno (right on the photo) carried out comprehensive analysis of the literature approaches and combined that with extensive experiments. As a result he was able to propose and convincingly justify one approach, which has merits over others and should be used for evaluation of LoD.
The work led by Dr Riin Rebane (photo on the left) resulted in APCI ionization efficiency scale containing 40 compounds with widely ranging chemical and physical properties and spanning 5 orders of magnitude of ionization efficiency. Analysis of the resulting data challenges the common knowledge about APCI as ionization method. Contrary to the common knowledge, ionization efficiency order in the APCI source is surprisingly similar to that in the ESI source and most of the compounds that are best ionized in the APCI source are not small volatile molecules. Large tetraalkylammonium cations are a prominent example. These findings suggest that the atmospheric pressure chemical ionization mechanism can be more complex than generally assumed and most probably several ionization mechanisms operate in parallel and a mechanism not relying on evaporation of neutral molecules from droplets has significantly higher influence than commonly assumed.
The LC-MS group at the UT Institute of Chemistry were recently invited by the journal Analytica Chimica Acta to write a tutorial review on the topic of validation of liquid chromatography mass spectrometry (LC-MS) methods. This work has now been completed. The tutorial review intends to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC–MS), especially with electrospray ionisation (LC-ESI-MS), and discuss specific issues that arise with MS (and MS-MS) detection (i.e. LC-MS-MS) in LC (as opposed to the “conventional” detectors). The review was eventually split in two parts (because of its large volume):
(as an April joke from Elsevier, part II appears page-wise before part I)
The review addresses and compares all the major validation guidelines published by international organizations: ICH, IUPAC, AOAC, FDA, EMA (EMEA), Eurachem, SANCO, NordVal, European Commission Decision 2002/657/EC. With every performance characteristic the tutorial review briefly compares the recommendations of the guidelines.
The Part I briefly introduces the principles of operation of LC–MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. The Part II starts with briefly introducing the main quantitation methods and then addresses the performance related to quantification: linearity of signal, sensitivity, precision, trueness, accuracy, stability and measurement uncertainty. The last section of Part II is devoted to practical considerations in validation and a possible step by step validation plan specifically suitable for LC-MS-MS is presented.
With every method performance characteristic its essence and terminology are addressed, the current status of treating it is reviewed and recommendations are given, how to determine it, specifically in the case of LC–MS methods. In many cases the published guidelines remain too general for practicing analyst. This tutorial review gives more specific advice based on the best available practice.
Based on the recommended approaches presented in this tutorial review an LC-MS validation software ValChrom is currently under development by the UT team. The software development is supported by the EU Regional Development Fund (Development of software for validation of chromatographic methods, Project No. 3.2.1201.13-0020).
Every year Estonian University of Life Sciences organises a conference called “Healthy animal and healthy food” where Dr. Riin Rebane made a presentation “Fight against food fraud” which explained the ever-expanding role of analytical chemists in food science. Reasons for food fraud vary, but are almost always for monetary gain and therefore food fraud is in constant progress. One good example is honey analysis, where for decades there has been a change in methods in order to identify whether honey is real or whether it is identified with correct botanical or geographical origin. As a natural product, no two honeys are identical and this makes identification further more challenging for the chemists. One of the possible methods is amino acid analysis since the amino acid content can be like a fingerprint for honeys and in University of Tartu we have analysed few hundreds of Estonian honeys and have seen that that foreign honeys do differ in most cases and also that there is a correlation between the amino acid content and botanical origin. But nevertheless, even this method might not work every time and chemists are looking towards methods such as nuclear magnetic resonance spectroscopy and even DNA-analysis to get better certainty for determining the origin of honey.
