All presented studies aimed on the improvement of the quality analysis of already monographed drugs. Thereby different LC methods were applied and coupled to i.e., the UV/VIS detector, the CAD or a hyphenation of these detectors, respectively. The choice of the chromatographic system including the detector was largely dependent on the physicochemical properties of the respective analytes. With the risk-assessment report on the API cetirizine we presented an exemplary tool, that can help to minimize the risk of the occurrence of unexpected impurities. An in- deep analysis of each step within synthesis pathway by means of reaction matrices of all compounds was performed. It is essential to understand the complete impurity profile of all reactants, solvents, and catalysts and to include them in the matrix. Finally, the API of this synthesis was checked if all impurities are identified by this tool. Of note, a shortcoming of such a targeted approach is that impurities can still occur, but they are not captured. This disadvantage can be partially compensated by non-targeted approaches if they are performed in parallel with the other studies that represent most of the impurities. However, this work also shows that even in a supposedly simple synthesis, potentially hundreds of by-products can be formed. For each of them, it must be decided individually whether their formation is probable or how their quantity can be minimized in order to obtain APIs, that are as pure as possible. In the dapsone project it was aimed to replace the existing old Ph. Eur. TLC method with a modern RP-HPLC method. This was successful and since Ph. Eur. 10.6, the method developed in this work, became a valid monograph. Within the revision process of the monograph, the individual limits for impurities were tightened. However, this new method needs HPLC instrumentation, suitable to perform gradients. As this is not always available in all control laboratories, we also developed an alternative, more simple method using two different isocratic runs for the impurity analysis. The obtained batch results of both, the new pharmacopoeial method and the more simple one, were in a comparable order of magnitude. Furthermore, within the method development stage of the Ph. Eur. method, we could identify one unknown impurity of the impurity reference by high-resolution MS/MS analysis. Also, in the baclofen project it was aimed to replace the existing Ph. Eur. method with the introduction of an additional impurity to be quantified. A corresponding method was developed and validated. However, due to the harmonization process of the pharmacopoeias, it is currently not used. In addition, we tried to find further, non- 116 SUMMARY chromophoric impurities by means of the CAD. However, except for one counterion of an impurity, no further impurities were found. Also, the aforementioned new impurity could not be detected above the reporting threshold in the batches analyzed. As the only individually specified impurity A is also present at a low level, it can be concluded that the examined batches of baclofen are very pure. The use of universal detectors, such as the CAD can be particularly interesting for compounds with no chromophore or those with only a weak chromophore. Therefore, we decided to take a closer look at the impurity profile of acarbose. Currently, acarbose and its impurities are being studied by low wavelength UV detection at 210 nm. Therefore, the question arose whether there are no other impurities in the API that do not show absorption at this wavelength. CAD, which offers consistent detection properties for all non-volatile compounds, is ideally suited for this purpose. However, it was not so easy to use the CAD together with the UV detector, for example, as a hyphenated detection technique, because the Ph. Eur. method uses phosphate buffers. However, this is non-volatile and therefore inappropriate for the CAD. Therefore, an attempt was made to replace the buffer with a volatile one. However, since this did not lead to satisfactory results and rather the self-degradation process of the stationary phase used could be observed by means of the CAD, it was decided to switch to alternative stationary phases. A column screening also revealed further difficulties with acarbose and its impurities: they show an epimerization reaction at the end of the sugar chain. However, since one wanted to have uniform peaks in the corresponding chromatograms, one had to accelerate this reaction significantly to obtain only one peak for each component. This was best achieved by using two stationary phases: PGC and Amide-HILIC. Impurity-profiling methods could be developed on each of the two phases. In addition, as expected, new impurities could be detected, albeit at a low level. Two of them could even be identified by spiking experiments as the sugar fragments maltose and maltotriose. Taken together, it can be concluded, that this work has contributed significantly to the improvement of the quality analysis of monographed drugs. In addition to the presented general tool for the identification of potential impurities, one of the methods developed, had already been implemented to the Ph. Eur. In an effort to improve the CAD's universal detection capabilities, additional methods have also been developed. Further, new improved methods for the impurity profiling are ready to use.

The charged aerosol detector (CAD) is an aerosol-based detector employed in liquid chromatography which has become established in the field of pharmaceutical analysis due to its outstanding performance characteristics, e.g. the almost uniform response for nonvolatile analytes. Owing to its principle of detection, the response of the CAD depends on the volatility of a compound and is inherently nonlinear. However, the newly implemented instrumental settings evaporation temperature and power function value (PFV) are valuable tools to overcome some of these drawbacks and can even enhance the detector’s capabilities when adjusted properly. This thesis aimed to evaluate the impact of the new instrumental settings on the CAD performance. Additionally, the influence of modern separation techniques for small polar compounds on the CAD was assessed and the applicability of hyphenated UV-CAD techniques explored. The optimization strategies derived from the evaluation procedures and the conjunction of the instrumental and chromatographic techniques investigated were utilized for the challenging impurity profiling of amino acids and amino acid-like drugs. The results of the method validation procedures confirmed the broad applicability of the CAD in the pharmaceutical analysis of nonvolatile compounds, supported by satisfactory sensitivity and reproducibility for meeting the regulatory requirements with respect to the ICH guidelines Q2(R1) and Q3A(R2). The limits of applicability include the analysis of semivolatile compounds, and the method transfer between current and legacy CAD models. Further advances in the definition and standardization of allowed ranges for the instrumental settings and the establishment of general optimization procedures in the method development could lead to a more widespread use of the detection technique in compendial methods.

Liquid chromatography has become the gold standard for modern quality control and purity analytics since its establishment in the 1930s. However, some analytical questions remain very challenging even today. Several molecules and impurities do not possess a suitable chromophore for the application of UV detection or cannot be retained well on regular RP columns. Possible solutions are found in derivatization procedures, but they are time consuming and can be prone to errors. In order to detect non chromophore molecules underivatized, the concept of aerosol based universal detection was established with the introduction of the evaporative light scattering detector (ELSD) in the 1970s and the charged aerosol detector (CAD) followed in 2002. These two challenging fields – polar and non chromophore molecules – are tackled in this thesis. An overview of applications of the CAD in the literature and a comparison to its aerosol based competitors and MS is presented, emphasizing on its high sensitivity and robustness. Parameters and techniques to overcome the drawbacks of CAD, such as the use of gradient compensation or adjusted evaporation temperatures are discussed. A consideration of aspects and drawbacks of data transformation such as the integrated power function value (PFV) in the GMP environment is performed. A method for the fatty acid analysis in polysorbate 80 that was developed on HPLC CAD was transferred to UHPLC CAD. Time and eluent savings of over 75% and 40%, respectively, as well as ways to determine the optimal CAD parameters resulted from this investigation. The evaporation temperature was determined as the most crucial setting, which has to be adjusted with care. Optimal signal to noise ratios are found at a compromise between maintaining analyte signal and reducing background noise. The incorporation of semi volatile short chain fatty acids enabled the observation of differences based on volatility of the analyte. E.g. for semi volatiles, an improved linearity by means of adjusting the PFV is achieved at values below 1.0 instead of at elevated PFVs. Using sugars and sugar related antibiotics, a proof-of-concept was given that artificial neural networks can describe correlations between the structure and physicochemical properties of molecules and their response in CAD. Quantitative structure property relationships obtained by design of experiment approaches were able to predict the response of unseen substances and yielded insights on the response generation of the detector, which heavily relies on the formed surface area of the dried particle. Further work can substantiate upon these findings, eventually building a library of diverse eluent compositions, analytes and settings. In order to cope with a chromatographically challenging substances, the application of ion pairing reversed phase chromatography coupled to low wavelength UV detection has been shown as a possible approach for the amino acid L asparagine. A method capable of compendial purity analysis in one single HPLC approach, thus making the utilization of the semi quantitative TLC-ninhydrin analysis obsolete, resulted from this. One cyclic dipeptide impurity (diketoasparagine) that was formerly not assessed, could be identified in several batches and added to the monograph of the Ph.Eur. Studying ibandronate sodium with CAD and ELSD, it was found that randomly occurring spike peaks represent a major flaw of the ELSD when high sample load is present. The research with this non chromophore bisphosphonate drug furthermore shed light on possible drawbacks of mixed mode chromatography methods and ways to overcome these issues. Due to strong adsorption of the analyte onto the column, over ten injections of the highly concentrated test solution were found to be necessary to ensure reproducible peak areas. Preconditioning steps should thus be evaluated for mixed mode approaches during method development and validation. Last, using a ternary mixed mode stationary phase coupled to CAD, a method for the impurity profiling of pamidronate disodium, also applicable to the assessment of phosphate and phosphite in four other bisphosphonate drugs, has been developed. This represents a major advantage over the Ph.Eur. impurity profiling of pamidronate, which requires two different methods, one of which is only a semi quantitative TLC approach.

Der Gruppe der Macrogole sowie den darauf basierenden Abkömmlingen, den Macrogolfettalkoholethern, Macrogolfettsäureestern und Polysorbaten, kommt in der modernen Galenik eine wichtige Rolle zu. Dienten sie vormals nur als gewöhnliche Emulgatoren, so finden sie heutzutage vor allem im Bereich der gezielten Wirkstofffreisetzung, der Erhöhung der Bioverfügbarkeit sowie als Löslichkeitsvermittler komplexer Systeme Anwendung. Diese vielschichtigen Anwendungsgebiete erfordern, auch aufgrund der polydispersen Strukturen der Macrogole, eine reproduzierbare und aussagekräftige Analytik. Das Europäische Arzneibuch (Ph. Eur.) bietet zur Charakterisierung der Hilfsstoffe eine Handvoll Messgrößen, die sog. Fettkennzahlen, die eine Größenordnung vorhandener funktioneller Gruppen liefern. Zu diesen gehören Werte wie Hydroxylzahl, Iodzahl, Peroxidzahl oder Säurezahl. Diese bieten zwar einen Überblick über den Größenbereich der mittleren Kettenlängen oder einen möglichen Abbau der Strukturen, beispielsweise durch Autoxidation, jedoch geben sie keine Auskunft über die Polymerverteilung. Insbesondere diese kann jedoch, je nach Herstellungsweise, stark variieren. Außerdem ist die Methodik der Fettkennzahlenbestimmungen aufgrund der strikten Reaktionsabläufe und zahlreicher Reaktionsschritte einerseits sehr zeitaufwändig und andererseits anfällig für Fehler. Die HPLC hat, insbesondere aufgrund der Automation, bereits seit Jahren den Status des Goldstandards in der pharmazeutischen Analytik inne. Gekoppelt mit der UV-Detektion bietet sie für zahlreiche Wirkstoffe die Möglichkeit zur schnellen, einfachen und robusten Analyse. Im Bereich der Hilfsstoffe verbreitet sich die HPLC-Analytik langsamer, da viele Hilfsstoffe keinen Chromophor aufweisen. Eine Anwendung der hochsensitiven Massenspektrometrie wäre zwar zur Detektion geeignet, würde sich für die Routineanwendung jedoch als zu komplex und kostenintensiv gestalten. Doch mit der Entwicklung der Aerosol-basierten Detektoren wie dem ELSD (evaporative light scattering detector), dem CAD (charged aerosol detector) und dem NQADTM (nano quantity aerosol detector) wurde auch für nicht-chromophore Substanzen ein Einsatz der HPLC möglich. Die vorliegende Arbeit befasste sich mit der Entwicklung einer HPLC-CAD-Methode, die eine möglichst große Bandbreite der Macrogole und der darauf basierenden Hilfsstoffe erfassen kann. Die Trennung erfolgte an einer C18-Trennsäule. Es wurde eine Gradienten-Methode entwickelt, die aus mehreren linearen Gradientenstufen zusammengesetzt wurde, um verschiedene Kettenlängen der Polymere besser voneinander zu trennen. Als mobile Phasen dienten Wasser und Acetonitril, denen jeweils 0.1 % Ameisensäure zugesetzt wurden. Es konnten Macrogole im Bereich PEG 300 bis PEG 3000 mit akzeptabler Auflösung aufgetrennt werden. Diese Ergebnisse wurden für PEG 300 – 1500 mittels Massenspektrometrie verifiziert. Es konnten fünf gesättigte und zwei ungesättigte Fettsäuren, sowie zwei Fettalkohole verschiedener Kettenlängen voneinander getrennt werden. Es wurden 13 Macrogol-basierte Hilfsstoffe mit der entwickelten Methode untersucht und erfolgreich getrennt. Die Macrogolfettalkoholether, -stearate und Polysorbate wurden insoweit aufgetrennt, dass die Polymerverteilung beobachtet werden konnte. Freie PEGs in den Hilfsstoffen wurden getrennt und identifiziert. Anhand dieser konnten unterschiedliche Herstellungsweisen zugeordnet werden. Abhängig von der mittleren Kettenlänge der verarbeiteten PEGs konnten teilweise die freien Fettsäuren bzw. -alkohole von den Estern bzw. Ethern getrennt und identifiziert werden. Im Bereich der kürzeren mittleren Kettenlängen wurden die freien Fettsäuren und -alkohole von den Estern und Ethern überlagert. Macrogolglycerolhydroxystearat (Cremophor® RH40) wurde in seine Komponenten aufgetrennt, mit Ausnahme der linearen Monoester, die mit den freien PEGs partiell koeluierten und die Glyceroltriester, die Größenausschlusseffekte zeigten. Die Methode wurde für Stabilitätsuntersuchungen der ungesättigten Fettsäuren, Öl- und Linolsäure, eingesetzt. Hierzu wurden diese Säuren in Lösung chemisch (Wasserstoffperoxid) und thermisch (60 °C) gestresst und in bestimmten Zeitabständen analysiert. Es zeigte sich ein zeit- und temperaturabhängiger Abbau. Die teilweise Zuordnung der Abbauprodukte erfolgte durch Bestimmung des m/z mittels Massenspektrometrie. Die Methode war geeignet, um das Ausmaß eines oxidativen Abbaus von der Hauptsubstanz zu trennen und strukturell einzuordnen. Generell bietet die Methode eine gute Basis, die eine Vielzahl an Substanzgruppen erfassen und charakterisieren kann. Sie bietet eine Ergänzung der Fettkennzahlen, die einen verringerten Arbeitsaufwand mit sich bringt. Für spezifischere Betrachtungen (Langzeitstabilität, verwandte Substanzgruppen) stellt sie einen guten Ausgangspunkt dar.

In the first part of his work, the causes for the sudden degradation of useable capacity of lithium-ion cells have been studied by means of complementary methods such as computed tomography, Post-Mortem studies and electrochemical analyses. The results obtained point unanimously to heterogeneous aging as a key-factor for the sudden degradation of cell capacity, which in turn is triggered by differences in local compression. At high states of health, the capacity fade rate is moderate but some areas of the graphite electrode degrade faster than others. Still, the localized changes are hardly noticeable on cell level due to averaging effects. Lithium plating occurs first in unevenly compressed areas, creating patterns visible to the human eye. As lithium plating leads to rapid consumption of active lithium, a sudden drop in capacity is observed on cell level. Lithium plating appears to spread out from the initial areas over the whole graphite electrode, quickly consuming the remaining useful lithium and active graphite. It can be hypothesized that a self-amplifying circle of reciprocal acceleration of local lithium loss and material loss causes rapid local degradation. Battery cell designers can improve cycle life by homogeneous pressure distribution in the cell and using negative active materials that are resilient to elevated discharge potentials such as improved carbons or lithium titanate. Also, a sufficiently oversized negative electrode and suitable electrolyte additives can help to avoid lithium plating. When packs are designed, care must be taken not to exert local pressure on parts of cells and to avoid both very high and low states of charge. In the second part of this dissertation the resilience of cylindrical and pouchbag cells to shocks and different vibrations was investigated. Stresses inflicted by vibration and shock tests according to the widely recognized UN38.3 transport test were compared to a long-time test that exposed cells to a 186 days long ordeal of sine sweep vibrations with a profile based on real-world applications. All cells passed visual and electric inspection performed by TU München after the vibration tests. Only cylindrical cells subjected to long-term vibrations in axial direction showed an increase in impedance and a loss of capacity that could be recuperated in part. The detailed analyses presented in this thesis gave more details on the damages inflicted by vibrations and shocks and revealed drastic damages in some cases. In cylindrical cells, only movement in axial direction caused damage. Long term vibrations were found to be especially detrimental. No damage whatsoever could be detected for pouch cells, regardless of the test protocol and the direction of movement. The extreme resilience of pouchbag cells shows that the electrode stack of lithium-ion cells is resistant to vibrations, and that damages are caused by design imperfections that can be improved at low cost. The findings of this work, and the general state of research show that it is most crucial to control the lithiation and thus potential of the graphite electrode. In the last part of this work, a new, direct method for charge estimation based on changing transmission is presented. A correlation between transmission of short ultrasonic pulses and state of charge is found. This new technology allows direct measurement of the state of charge. The method is demonstrated for batteries with different positive active materials, showing its versatility. As the observed changes can be traced to the lithiation of graphite, it can be determined without a reference electrode. Already at this early stage of development, the found correlations allow estimation of state of charge. The present hysteresis in the signal height of the slow wave, which is unneglectable especially during discharging at higher currents, will be subject to further investigation. The observed effects can be explained by effects on different length scales. Biot’s theory explains the second wave’s slowness based on the active material particles size in the range of 0.01 mm and electrolyte-filled pores. Lithiation of graphite changes the porosity of the electrode and thereby the velocity and wavelength of the impulse. When the wavelength approaches the length scale of the layers, 0.1 mm, scattering effects dampen the transmitted signal. Finally, the wavelength of the pulse should be shorter than the transducers diameter to obtain a homogeneous wave front. To conclude, the new method allows the control of each individual cell in a pack independent from the electrical connections of the cells. As the method shows great promise, further studies regarding factors such as long-term behavior, temperature and current rates should be conducted. In this thesis hysteresis was observed and a deeper understanding of the reasons behind it may allow further improvements of measurement precision.