@phdthesis{Pawellek2021,
  author    = {Pawellek, Ruben},
  title     = {Charged Aerosol Detector Performance Evaluation and Development of Optimization Strategies for the Analysis of Amino Acids},
  doi       = {10.25972/OPUS-24319},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-243197},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {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.},
  subject      = {Instrumentelle Analytik},
  language  = {en}
}
@phdthesis{Becht2022,
  author    = {Becht, Alexander Ulrich},
  title     = {New applications for spectroscopic and chemometric studies of drugs},
  doi       = {10.25972/OPUS-27534},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-275342},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Spectroscopic methods were established decades ago in a wide variety of fields. This also applies to the pharmaceutical field, although they initially were mostly used for identity testing or structure elucidation only. Technical developments, such as miniaturization (NMR benchtop devices), Fourier transformations (for NMR, MIR spectroscopy) or the combination with chemometric evaluation (e.g., in Process Analytical Technology, PAT), have further increased their importance and opened up new applications. The aim of this work was to investigate further new approaches and to find new applications for already established methods and to show their benefits. By means of MIR, NIR and NMR data and their chemometric evaluation (principal component analysis, PCA; hierarchical cluster analysis, HCA; linear discriminant analysis, LDA), possibilities were presented to successfully determine the manufacturer or the pharmaceutical company of various paracetamol preparations. In the course of this, various similarities and correlations between the preparations of individual companies could also be identified. For this purpose, a suitable sample preparation was developed for each spectroscopic method, and suitable measurement parameters in order to obtain reproducible spectra for the chemometric evaluation were determined. Furthermore, the results of the two unsupervised methods (HCA, PCA) were compared with each other. The HCA was able to confirm those of the PCA for the very most part. Additionally, through these methods it was possible to characterize many of the preparations based on clusters formed by comparable tablet compositions. In order to be able to measure unmortared, whole tablets using the NIR spectrometer, an attachment was developed and manufactured using 3D printing. Its functionality was demonstrated by measuring and analyzing the tablets of two different batches of nine paracetamol preparations. The batches were clearly distinguished on the basis of a PCA and a significant difference was also demonstrated by means of statistical tests. For NMR spectroscopy, a method was developed to obtain optimized "fingerprint" spectra of drug formulations. For this purpose, a 1D DOSY measurement was elaborated, in which the signals of the active ingredient could be filtered out by the appropriate choice of measurement parameters. The chemometric evaluation can thus focus on the remaining signals of the excipients, on the basis of which the preparations of the same API can be distinguished. Especially in the case of formulations that consist largely of active ingredient, data pre processing of the spectra can thus be simplified and greater importance can be assigned to the originally very small excipient signals. A quantitative 1H NMR method was developed for the comparison of a high field spectrometer (400 MHz) with a benchtop spectrometer (80 MHz) for two finished drugs. It was shown that it is possible to obtain comparable results with both instruments, but that the influence of the excipients on the signals and the lower resolution of the benchtop instrument must be taken into account. Therefore, it was not possible to obtain comparable results without further optimization of the method for one of the active ingredients. In the investigation of various reactions between APIs and excipients using DOSY, its usefulness as a screening method in stability testing was demonstrated. For this purpose, three different APIs and excipients were stressed together and the reaction mixtures were subsequently measured using DOSY. Based on the translational diffusion coefficient, the reaction products could be identified and distinguished from the active ingredients and the excipients used. The importance of thoughtful processing could also be demonstrated. If all peak heights are selected when evaluating signals split by direct spin spin coupling, this allows the detection of hidden signals as long as not all signals have the same diffusion coefficient. The selective selection of individual peak heights in the case of split signals also enables the evaluation of signals that overlap slightly. However, the limitations of this method were also shown when two signals overlap too much and differ too little in their diffusion coefficients. Hence, it has been successfully demonstrated in the various projects that the new chemometric approaches, as well as the new applications of already established methods, enable in depth findings and thus have a clear added value.},
  subject      = {Instrumentelle Analytik},
  language  = {en}
}
@phdthesis{Leistner2023,
  author    = {Leistner, Adrian Dieter},
  title     = {Improving the quality analysis of monographed drugs - dapsone, baclofen, acarbose and other selected APIs},
  doi       = {10.25972/OPUS-30331},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-303318},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {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.},
  subject      = {Instrumentelle Analytik},
  language  = {en}
}