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The primary focus of my work is the application of informatics methods to the fields of materials science and analytical chemistry. The statistical analysis of data has become increasingly important in understanding the properties of materials and analytes. Statistical methods like principal component analysis (PCA) and multivariate curve resolution (MCR) are widely used for analysis in chemistry and other fields given their ability to categorize spectra in an unsupervised way. PCA is relatively easy to apply and has appealing mathematical properties. However, the results can be challenging to interpret, even for experienced users. In contrast, MCR results can be more interpretable, because the factors resemble real spectra and do not have negative scores or loadings. Nevertheless, the useful orthogonality properties of the scores and loadings in PCA are sacrificed in doing so. Other statistical analysis methods like cluster analysis and partial least squares regression (PLS-R) present their own challenges. Pattern recognition entropy (PRE) is a novel application of Shannon’s information theory for understanding the underlying complexity in spectra. Unlike PCA and MCR, PRE is a summary statistic that adopts the mathematical quantification of information and applies it for chemometric analysis. PRE values reflect the shape and complexity of spectra. Chapter 1 contains a description of the analytical methods/instruments that provided the data I analyzed by PRE and other informatics tools, including (i) X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) and (ii) liquid chromatography-mass spectrometry (LC-MS) and capillary electrophoresis (CE), (iii) a discussion of some of the commonly used statistical analysis tools like PCA, MCR, cluster analysis and PLS-R, and (iv) a description of PRE. Chapter 2 describes in much greater detail the theory associated with the statistical tools I used and PRE. Chapter 3 describes the PRE and informatics analysis of depth profiles through thin films by XPS and ToF-SIMS. Chapter 4 introduces the concept of the ‘reordered spectrum’ as an intuitive, visual representation of spectra to address the abstraction associated with PRE result. Total ion current chromatograms (TICCs) generated using LC-MS are often extremely complex and ‘noisy’. Chapter 5 describes the application of PRE as a variable reduction method for producing higher quality TICCs. Chapter 6 discusses the limitations associated with the application of PRE to TICCs and presents a new method using cross-correlation (CC) in conjunction with a PRE analysis. Chapter 7 discusses a new methodology that uses CE and PRE to detect autologous blood doping (ABD). Chapter 8 presents my conclusions of this present work and discusses the scope of future work on PRE. The thesis also contains several appendices. Appendix 1 introduces polyallylamine (PAAm) as a simple, easy-to-apply adhesion promoter for the widely used photoresist SU-8. Appendices 2, 3 and 4 contain articles I wrote that relate to trends in modern XPS instrumentation and 5-8 contain supplemental information relating to Chapters 3, 4, 5, and 7 respectively.

Background: Pulmonary Embolism (PE) is a potentially life-threatening condition that is characterized by one or several blood clots blocking the arteries in the lungs. The existing diagnostic tools for PE have their shortcomings, highlighting the importance of investigating new diagnostic methods. The development of non-invasive methods to collect microparticles from exhaled breath has opened possibilities to explore new potential biomarkers. SensAbues® is a sampling device that utilizes electrostatic filters to capture microparticles from the exhaled breath. The objective of this project was twofold: firstly, to assess the suitability of SensAbues® sampling device for a future proteomics study where the goal is to identify biomarkers for PE; and secondly, to evaluate the efficacy of various extraction solutions in retrieving proteins from the electrostatic filters. Materials and methods: Samples were collected from three healthy volunteers using the SensAbues® device. The electrostatic filters were then extracted using either PBS or 15% ethanol and the protein content was then estimated using a modified Bradford method. Additionally, two blank SensAbues® filter extracts, from PBS and 15% ethanol were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Results: The attempts to evaluate extraction solutions using the Bradford method were unsuccessful, as all the samples yielded negative values. The filter-blank extracts analyzed with LC-MS/MS contained a significant amount of polyethylene glycols of varying sizes. Conclusion: The polyethylene glycols from the SensAbues® filters may have interfered with the Bradford method. Polyethylene glycols can also interfere with proteins, making the SensAbues® sampling device unsuitable for the prospective proteomics study.

Topical inquiries for the Swedish Defence Research Agency (FOI) include analysis of explosive substances in different sample types. Research into explosives in complex matrixes can provide an analytical support function for forensic investigation i.e. tools for areas such as finding bomb factories, identification and risk analysis of home-made explosives (HME) and improvised explosive devices (IED) as well as preventive measures against maliciously intended use of explosives. Additionally, the research may lay the groundwork for indications of health- and environmental hazards. Utilizing state-of-the-art equipment and years of extensive expertise, FOI is able to carry out these types of research tasks to provide security and sustainability for society. The aim of this thesis project is to establish and validate developed methods for collecting, extracting, separating, and detecting trace amounts of explosives in various bodies of water using a solid-phase extraction (SPE) robot and a high-resolution (HR) mass spectrometer (MS) connected to an ultra-high-performance liquid chromatograph (UHPLC). Particular areas of interest include locations in the Stockholm archipelago where experimental detonations of explosives have taken place. Overall, UHPLC-HRMS analysis provides a powerful tool for analyzing explosives in complex matrixes with unambiguous and reliable measurement data. The compounds of investigation were hexogen (RDX), octogen (HMX), pentyl (PETN), and trotyl (TNT). To summarize, during the course of the thesis, trace amounts of some explosives were detected and quantified in various bodies of water. Furthermore, the applied method for the project was successful in qualitatively and quantitatively analyze the compounds of interest with limit of detection ranging between 0.33–11 μg/L (ppb) in various water sources.

The aim of the present study was the development of analytical methods which can be used for gaining a deeper insight into the mechanisms of hair treatment with cosmetic formulations like shampoos. The efficacy of such a formulation is affected by the amount of different active agents remaining on the hair after treatment. Due to the complex composition of most of the formulations various dependencies and interactions of the ingredients are possible. Beneath that a variety of parameters of the treatment process influence the substantivity. Finally the degree of hair damage present at the treatment process is significant. So the process of hair treatment with cosmetic formulations is very complex. The understanding of this process enables a systematic development of products with better or novel effectivity. The developed analytical methods provide the possibility of a parallel determination of different active agents and their interaction of the adsorption behaviour. Furthermore the determination of influencing variables like treatment conditions or hair damage can be performed. So it is possible to generate the knowledge necessary for excellent scientific product development. The general methodology for the method development consists of an extraction from hair followed by a selective and sensitive quantitation of the active agents located in the extract using LC/MS and LC/MS/MS. Analytical methods for the determination of the complex composed surface active agents Sodium Laureth Sulfate, Cocamidopropyl Betaine and Alkyl Polyglucoside were developed. During the evaluation process it could be figured out that significant swelling of the hair fibre does not occur during a hair wash lasting 2 min or less. Hence the active agents are mainly adsorbed at the hair surface. During method development it was found that the composition of these agents is changing during hair treatment resulting in a difference of the singles substance distribution on hair and in the shampoo. Additionally an analytical method for selective and sensitive quantitation of the cationic polysaccharides Polyquaternium-10 and Guar Hydroxypropyltrimonium Chloride using LC/MS was developed. The parallel quantitation of Polyquaternium-10 and Guar Hydroxypropyltrimonium Chloride enables to study their interaction of the adsorption behaviour. Beneath that the quantitation of substances with low active contentes, like Ubiquinone 50, Piroctone Olamine and Benzophenone?4, was carried out. The extraction behaviour of these substances showed that an extraction time of 7 min assisted by an ultrasonic treatment is optimal. Longer extraction leads to a significant increase of the active hair surface due to swelling. The result is a higher adsorption capacity of the hair fibre and thus a decreased analyte concentration in the extract. The reproducibility of the using treatment protocol was approved by parallel quantitation of several active agents. Due to variation of several treatment parameters their influence on substantivity was studied: the flow rate, temperature and hardness of the water for rinsing and the time for massaging in the formulation. Furthermore, it was shown that the degree of hair damage and further shampoo ingredients influence the substantivity of active agents. Finally it was demonstrated that the adsorption behaviour can be significantly influenced by the application strategy. / Das Ziel der vorliegenden Arbeit war es, mit der Entwicklung von analytischen Methoden eine Möglichkeit zu schaffen, um die Mechanismen bei der Haarbehandlung mit kosmetischen Formulierungen, wie Shampoos besser verstehen zu können. Die Pflegeleistung einer solchen Formulierung wird unter anderem davon bestimmt, wie viel der unterschiedlichen eingesetzten Wirkstoffe nach der Behandlung auf dem Haar verbleiben. Durch die Komplexität der kosmetischen Formulierungen kommt es zu vielfältigen Abhängigkeiten und Beeinflussungen der Substantivität der einzelnen Substanzen voneinander. Darüber hinaus gibt es eine Vielzahl von Parametern bei der Haarbehandlung, die die Substantivität beeinflussen. Schließlich spielt auch der Zustand des Haares eine entscheidende Rolle. Alles in allem handelt es sich bei der Behandlung des Haares mit kosmetischen Formulierungen um sehr komplexe Prozesse. Das Verständnis dieser Prozesse ermöglicht eine gezielte Entwicklung von Produkten mit besserem und zum Teil neuartigem Leistungsspektrum. Die entwickelten Analysenmethoden erlauben die parallele Bestimmung der auf dem Haar adsorbierten Menge verschiedener Wirkstoffe. Dadurch kann die gegenseitige Beeinflussung der Wirkstoffadsorption untersucht werden. Darüber hinaus ermöglicht das Methodenspektrum eine Bestimmung der Einflussgröße äußerer Parameter, wie der Waschbedingungen und innerer Parameter, wie der Haarschädigung. Damit ist es möglich, das notwendige Wissen für eine fortschrittliche, wissenschaftliche Produktentwicklung zu gewinnen. Der allgemeine Ansatz für die Entwicklung der Methoden beinhaltet eine Extraktion der Wirkstoffe vom Haar, gefolgt von einer selektiven und empfindlichen Quantifizierung im Extrakt mittels LC-MS und LC-MS/MS. Es wurden Analysenmethoden für die komplex zusammengesetzten oberflächenaktiven Wirkstoffe Sodium Laureth Sulfate, Cocamidopropyl Betaine und Alkyl Polyglucoside entwickelt. Dabei wurde durch Untersuchungen der Extraktion vom Haar bewiesen, dass die zweiminütige Haarwäsche nicht zu einem signifikanten Aufquellen des Haares führt, so dass die Wirkstoffe hauptsächlich an der Haaroberfläche adsorbiert werden. Außerdem wurde gezeigt, dass sich die Zusammensetzung dieser Wirkstoffe während der Haarwäsche ändert, so dass sich die Einzelsubstanzverteilung auf dem Haar von der im Shampoo unterscheidet. Des Weiteren wurde die selektive und empfindliche Quantifizierung der kationischen Polymere Polyquaternium-10 und Guar Hydroxypropyltrimonium Chloride durchgeführt. Die parallele Quantifizierung beider Konditionierungsstoffe ermöglicht die Untersuchung, in welchem Umfang sich beide Polymere in ihrem Adsorptionsverhalten beeinflussen. Bei der Methodenentwicklung für die Quantifizierung der Wirkstoffe Ubiquinone, Piroctone Olamine und Benzophenone-4 zeigte sich, dass eine Extraktion über 7 min im Ultraschallbad die besten Ergebnisse brachte. Bei längerer Extraktionszeit vergrößert sich die Oberfläche des Haares durch Quellung, so dass sich der Anteil an adsorbierten Analyten wieder erhöht. Die Reproduzierbarkeit der Haarwäsche mit dem verwendeten Waschprotokoll wurde bestätigt, indem verschiedene Wirkstoffe parallel auf dem Haar quantifiziert wurden. Durch Veränderung der Waschparameter Einmassierzeit sowie Durchflussmenge, Temperatur und Härte des Spülwassers wurde der Einfluss dieser Parameter auf die Substantivität der Wirkstoffe untersucht. Darüber wurde gezeigt, dass sowohl der Schädigungsgrad des Haares als auch andere auf dem Haar befindliche Shampoo-Bestandteile einen Einfluss auf die Substantivität von Wirkstoffen haben. Schließlich wurde an einem Beispiel gezeigt, dass man die Substantivität von Wirkstoffen nicht nur durch die Zusammensetzung der kosmetischen Formulierung, sondern auch durch die Art der Anwendung entscheidend beeinflussen kann.

The aim of the present study was the development of analytical methods which can be used for gaining a deeper insight into the mechanisms of hair treatment with cosmetic formulations like shampoos. The efficacy of such a formulation is affected by the amount of different active agents remaining on the hair after treatment. Due to the complex composition of most of the formulations various dependencies and interactions of the ingredients are possible. Beneath that a variety of parameters of the treatment process influence the substantivity. Finally the degree of hair damage present at the treatment process is significant. So the process of hair treatment with cosmetic formulations is very complex. The understanding of this process enables a systematic development of products with better or novel effectivity. The developed analytical methods provide the possibility of a parallel determination of different active agents and their interaction of the adsorption behaviour. Furthermore the determination of influencing variables like treatment conditions or hair damage can be performed. So it is possible to generate the knowledge necessary for excellent scientific product development. The general methodology for the method development consists of an extraction from hair followed by a selective and sensitive quantitation of the active agents located in the extract using LC/MS and LC/MS/MS. Analytical methods for the determination of the complex composed surface active agents Sodium Laureth Sulfate, Cocamidopropyl Betaine and Alkyl Polyglucoside were developed. During the evaluation process it could be figured out that significant swelling of the hair fibre does not occur during a hair wash lasting 2 min or less. Hence the active agents are mainly adsorbed at the hair surface. During method development it was found that the composition of these agents is changing during hair treatment resulting in a difference of the singles substance distribution on hair and in the shampoo. Additionally an analytical method for selective and sensitive quantitation of the cationic polysaccharides Polyquaternium-10 and Guar Hydroxypropyltrimonium Chloride using LC/MS was developed. The parallel quantitation of Polyquaternium-10 and Guar Hydroxypropyltrimonium Chloride enables to study their interaction of the adsorption behaviour. Beneath that the quantitation of substances with low active contentes, like Ubiquinone 50, Piroctone Olamine and Benzophenone?4, was carried out. The extraction behaviour of these substances showed that an extraction time of 7 min assisted by an ultrasonic treatment is optimal. Longer extraction leads to a significant increase of the active hair surface due to swelling. The result is a higher adsorption capacity of the hair fibre and thus a decreased analyte concentration in the extract. The reproducibility of the using treatment protocol was approved by parallel quantitation of several active agents. Due to variation of several treatment parameters their influence on substantivity was studied: the flow rate, temperature and hardness of the water for rinsing and the time for massaging in the formulation. Furthermore, it was shown that the degree of hair damage and further shampoo ingredients influence the substantivity of active agents. Finally it was demonstrated that the adsorption behaviour can be significantly influenced by the application strategy. / Das Ziel der vorliegenden Arbeit war es, mit der Entwicklung von analytischen Methoden eine Möglichkeit zu schaffen, um die Mechanismen bei der Haarbehandlung mit kosmetischen Formulierungen, wie Shampoos besser verstehen zu können. Die Pflegeleistung einer solchen Formulierung wird unter anderem davon bestimmt, wie viel der unterschiedlichen eingesetzten Wirkstoffe nach der Behandlung auf dem Haar verbleiben. Durch die Komplexität der kosmetischen Formulierungen kommt es zu vielfältigen Abhängigkeiten und Beeinflussungen der Substantivität der einzelnen Substanzen voneinander. Darüber hinaus gibt es eine Vielzahl von Parametern bei der Haarbehandlung, die die Substantivität beeinflussen. Schließlich spielt auch der Zustand des Haares eine entscheidende Rolle. Alles in allem handelt es sich bei der Behandlung des Haares mit kosmetischen Formulierungen um sehr komplexe Prozesse. Das Verständnis dieser Prozesse ermöglicht eine gezielte Entwicklung von Produkten mit besserem und zum Teil neuartigem Leistungsspektrum. Die entwickelten Analysenmethoden erlauben die parallele Bestimmung der auf dem Haar adsorbierten Menge verschiedener Wirkstoffe. Dadurch kann die gegenseitige Beeinflussung der Wirkstoffadsorption untersucht werden. Darüber hinaus ermöglicht das Methodenspektrum eine Bestimmung der Einflussgröße äußerer Parameter, wie der Waschbedingungen und innerer Parameter, wie der Haarschädigung. Damit ist es möglich, das notwendige Wissen für eine fortschrittliche, wissenschaftliche Produktentwicklung zu gewinnen. Der allgemeine Ansatz für die Entwicklung der Methoden beinhaltet eine Extraktion der Wirkstoffe vom Haar, gefolgt von einer selektiven und empfindlichen Quantifizierung im Extrakt mittels LC-MS und LC-MS/MS. Es wurden Analysenmethoden für die komplex zusammengesetzten oberflächenaktiven Wirkstoffe Sodium Laureth Sulfate, Cocamidopropyl Betaine und Alkyl Polyglucoside entwickelt. Dabei wurde durch Untersuchungen der Extraktion vom Haar bewiesen, dass die zweiminütige Haarwäsche nicht zu einem signifikanten Aufquellen des Haares führt, so dass die Wirkstoffe hauptsächlich an der Haaroberfläche adsorbiert werden. Außerdem wurde gezeigt, dass sich die Zusammensetzung dieser Wirkstoffe während der Haarwäsche ändert, so dass sich die Einzelsubstanzverteilung auf dem Haar von der im Shampoo unterscheidet. Des Weiteren wurde die selektive und empfindliche Quantifizierung der kationischen Polymere Polyquaternium-10 und Guar Hydroxypropyltrimonium Chloride durchgeführt. Die parallele Quantifizierung beider Konditionierungsstoffe ermöglicht die Untersuchung, in welchem Umfang sich beide Polymere in ihrem Adsorptionsverhalten beeinflussen. Bei der Methodenentwicklung für die Quantifizierung der Wirkstoffe Ubiquinone, Piroctone Olamine und Benzophenone-4 zeigte sich, dass eine Extraktion über 7 min im Ultraschallbad die besten Ergebnisse brachte. Bei längerer Extraktionszeit vergrößert sich die Oberfläche des Haares durch Quellung, so dass sich der Anteil an adsorbierten Analyten wieder erhöht. Die Reproduzierbarkeit der Haarwäsche mit dem verwendeten Waschprotokoll wurde bestätigt, indem verschiedene Wirkstoffe parallel auf dem Haar quantifiziert wurden. Durch Veränderung der Waschparameter Einmassierzeit sowie Durchflussmenge, Temperatur und Härte des Spülwassers wurde der Einfluss dieser Parameter auf die Substantivität der Wirkstoffe untersucht. Darüber wurde gezeigt, dass sowohl der Schädigungsgrad des Haares als auch andere auf dem Haar befindliche Shampoo-Bestandteile einen Einfluss auf die Substantivität von Wirkstoffen haben. Schließlich wurde an einem Beispiel gezeigt, dass man die Substantivität von Wirkstoffen nicht nur durch die Zusammensetzung der kosmetischen Formulierung, sondern auch durch die Art der Anwendung entscheidend beeinflussen kann.

Abstract : The major objective of our study is to investigate DNA damage induced by soft X-rays (1.5 keV) and low-energy electrons (˂ 30 eV) using a novel irradiation system created by Prof. Sanche’s group. Thin films of double-stranded DNA are deposited on either glass and tantalum substrates and irradiated under standard temperature and pressure surrounded by a N[subscript 2] environment. Base release (cytosine, thymine, adenine and guanine) and base modifications (8-oxo-7,8-dihydro -2’-deoxyguanosine, 5-hydroxymethyl-2’-deoxyuridine, 5-formyl-2’-deoxyuridine, 5,6-dihydrothymidine and 5,6-dihydro-2’-deoxy uridine) are analyzed and quantified by LC-MS/MS. Our results reveal larger damage yields in the sample deposited on tantalum than those on glass. This can be explained by an enhancement of damage due to low-energy electrons, which are emitted from the metal substrate. From a comparison of the yield of products, base release is the major type of damage especially for purine bases, which are 3-fold greater than base modifications. A proposed pathway leading to base release involves the formation of a transient negative ion (TNI) followed by dissociative electron attachment (DEA) at the N-g lycosidic bond. On the other hand, base modification products consist of two major types of chemical modifications, which include thymine methyl oxidation products that likely arises from DEA from the methyl group of thymine, and 5,6-dihydropyrimidine that can involve the initial addition of electrons, H atoms, or hydride ions to the 5,6-pyrimidine double bond. / Résumé: L'objectif majeur de ce projet étude est d'étudier les lésions d'ADN induites par les rayons X mous (1,5 keV) et des électrons de faible énergie (˂ 30 eV) à partir d'un nouveau système d'irradiation créé par le groupe du Pr. Sanche. De minces couches d'ADN double brin sont déposées soit sur du verre ou sur les substrats de tantale. Celles-ci sont irradiées sous une température et pression environnante, mais dans une atmosphère de N[indice inférieur 2]. Les bases relâchées (cytosine, la thymine, l'adénine et la guanine) et les produits de modification de base (8-oxo-7,8-dihydro-2'-désoxyguanosine, 5-hydroxyméthyl-2'-désoxyuridine, 5-formyl-2'-désoxyuridine, 5,6-dihydrothymine et 5,6-dihydrouridine) sont analysés et quantifiés par LC-MS/MS. Nos résultats révèlent un plus grand rendement de dommages dans les échantillons déposés sur le tantale que celles sur le verre. Cette différence peut être expliquée par l’interaction des électrons de faible énergie qui sont photo émis des substrats métalliques. D'après les résultats obtenus, la libération de bases est un produit majeur en comparaison avec la modification de bases. Ceci provient, en particulier, surtout des purines qui libèrent la base a un niveau trois fois plus grand que la modification de la base. Une voie proposée, conduisant à la libération de base, implique la formation d'ions négatifs transitoires (TNI), suivie par l'attachement d'électrons dissociatifs (DEA) à la liaison N-glycosidique. En outre, les produits de modification de base sont composés en deux grands types de modifications chimiques. L’un des produits est l’oxydation du groupe méthyle de la thymine, qui probablement consiste de en d'hydrure (-H[indice supérieur -]) par l'intermédiaire de DEA. Alors que l’autre modification chimique est la formation de 5,6-dihydropyrimidine qui implique l'addition d'hydrure à la double liaison du 5,6-pyrimidine.

<p>Disease-specific compounds (biomarkers) are analyzed in clinical laboratories to assist with diagnosing diseases. This thesis describes development and validation of liquid chromatography tandem mass spectrometry (LC-MS/MS) based tests for diagnosing a diverse group of endocrine and metabolic diseases. The analytical methods used on-line and off-line sample extraction and analytical derivatization as means of enhancing the analytical sensitivity, specificity and clinical utility. All developed methods were extensively validated and reference intervals for the biomarker concentrations were established in blood samples of healthy adults and children. Advantages of the LC-MS/MS as an analytical technique include possibility of simultaneous measurement of multiple analytes and ability of confirming their identity. In this thesis we proposed and evaluated approaches for the assessment of the specificity of analysis in the methods that use tandem mass spectrometry detection. To enhance throughput of the LC-MS/MS tests for the biomarkers that have endogenous or exogenous isomers an approach was developed for quantitation of isomers from unresolved chromatographic peaks. Using methods developed in this thesis we performed a study of the steroidogenesis in ovarian follicles of healthy women and women with polycystic ovary syndrome (PCOS). Obtained data on the steroid concentrations and associations between the steroid metabolites in the pathway would be helpful for better understanding of the ovarian pathophysiology. Potential biomarkers of PCOS were identified in the thesis; further studies will be necessary to confirm their clinical utility.</p>

Until now, most metabolomics protocols have been optimized towards high sample throughput and high metabolite coverage, parameters considered to be highly important for identifying influenced biological pathways and to generate as many potential biomarkers as possible. From an analytical point of view this can be troubling, as neither sample throughput nor the number of signals relates to actual quality of the detected signals/metabolites. However, a method’s selectivity for a specific signal/metabolite is often closely associated to the quality of that signal, yet this is a parameter often neglected in metabolomics. This thesis demonstrates the importance of considering selectivity when developing NMR and LC-MS metabolomics methods, and introduces a novel approach for measuring chromatographic and signal selectivity in LC-MS metabolomics. Selectivity for various sample preparations and HILIC stationary phases was compared. The choice of sample preparation affected the selectivity in both NMR and LC-MS. For the stationary phases, selectivity differences related primarily to retention differences of unwanted matrix components, e.g. inorganic salts or glycerophospholipids. Metabolites co-eluting with these matrix components often showed an incorrect quantitative signal, due to an influenced ionization efficiency and/or adduct formation. A novel approach for measuring selectivity in LC-MS metabolomics has been introduced. By dividing the intensity of each feature (a unique mass at a specific retention time) with the total intensity of the co-eluting features, a ratio representing the combined chromatographic (amount of co-elution) and signal (e.g. in-source fragmentation) selectivity is acquired. The calculated co-feature ratios have successfully been used to compare the selectivity of sample preparations and HILIC stationary phases. In conclusion, standard approaches in metabolomics research might be unwise, as each metabolomics investigation is often unique.  The methods used should be adapted for the research question at hand, primarily based on any key metabolites, as well as the type of sample to be analyzed. Increased selectivity, through proper choice of analytical methods, may reduce the risks of matrix-associated effects and thereby reduce the false positive and false negative discovery rate of any metabolomics investigation.