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A comparison of analytical techniques for the determination and monitoring of charge variants in therapeutic proteins : master's thesis
Eva Kropušek, 2023, master's thesis

Abstract: Charge variants of therapeutic proteins are considered to be drug product variants and process-related impurities. To monitor charge heterogeneity, the development of a new analytical method is needed. Imaged capillary isoelectric focusing, capillary zone electrophoresis, and cation exchange chromatography assays were evaluated as candidate assays to support the early development of two new biological drug candidates. These are the analytical techniques most frequently used in the pharmaceutical industry for monitoring charge heterogeneity. We compared the advantages and disadvantages of these analytical techniques for monitoring charge variants in two innovative monoclonal antibodies. The results obtained revealed similarities and differences in the various analytical techniques. However, there is only a short time-frame dedicated to analytical method development when developing new biological drugs. With this in mind, imaged capillary isoelectric focusing showed a perfect balance between the quality and speed of analysis.
Keywords: Imaged capillary isoelectric focusing, capillary zone electrophoresis, cation exchange chromatography, charge variants, biological drug
Published in DKUM: 03.10.2023; Views: 376; Downloads: 27
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Simultaneous GC-MS determination of free and bound phenolic acids in Slovenian red wines and chemometric characterization
Milena Ivanović, Maša Islamčević Razboršek, Mitja Kolar, 2016, original scientific article

Abstract: Several phenolic acids (PAs), caffeic, vanillic, syringic, p-coumaric and ferulic acid, found in Slovenian red wines were studied using gas chromatography and mass spectrometry (GC-MS). For isolation of the PAs from wine samples, solid phase extraction (SPE) using hydrophilic modified styrene - HLB cartridges was used. The bound PAs were extracted after basic hydrolysis and o-coumaric acid was used as the internal standard (ISTD). The method developed was validated and the linear concentration range for all analytes was from 1 to 100 mg L$^{-1}$ with correlation coefficients above 0.999. We show that the method is repeatable (RSD<2%), recoveries were above 96%, and LOD and LOQ values were acceptable. In all of the wine samples tested, caffeic and p-coumaric acid were determined to be the predominant PAs (17-72 mg L$^{-1}$), while other compounds were found in lower concentrations. Principal Component Analysis (PCA) and Cluster Analysis (CLU) were used to study differences between wines related towards varieties and Slovenian wine regions. The results demonstrate that variety has more influence on PAs content than wine regions in Slovenian red wines.
Keywords: phenolic acids, Slovenian red wines, gas chromatography, mass spectrometry, PCA, CLU
Published in DKUM: 25.08.2017; Views: 1979; Downloads: 372
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Determination of topiramate in human plasma using liquid chromatography tandem mass spectrometry
Tanja Vnučec, Lea Cvitkovič-Maričič, Helena Prosen, Darinka Brodnjak-Vončina, 2013, original scientific article

Abstract: The LC-MS/MS method for determination of the anti-epileptic drug topiramate (TPM) in human plasma was developed and validated for pharmacokinetic and bioequivalence study purposes. For quantitative determination of TPM values the method with deuterated internal standard (topiramate-d12) and liquid chromatography with tandem mass spectrometry was used. TPM was extracted from the human plasma using the solid-phase extraction procedure on a Strata X extraction column. Negative ions were monitored in the selected reaction monitoring mode (SRM) and transitions m/z 338.2 > 78.2 and m/z 350.3 > 78.2 were used for the quantitative evaluation of TPM and the internal standard, respectively. The results obtained from validation were statistically evaluated according to the requirements of European Medicines Agency (EMA) and Food and Drug Administration (FDA) regulatory guidelines. The linearity of the method was checked within a concentration range from 10 to 2000 ng/mL. Successful validation confirmed that this method is precise, accurate, sensitive and therefore suitable for determination of topiramate plasma levels in pharmacokinetic and bioequivalence studies.
Keywords: topiramate, liquid chromatography tandem mass spectroscopy, human plasma, bioequivalence study
Published in DKUM: 18.08.2017; Views: 1428; Downloads: 96
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Determination of candesartan in human plasma with liquid chromatography - tandem mass spectrometry
Vanja Forjan, Lea Cvitkovič-Maričič, Helena Prosen, Darinka Brodnjak-Vončina, 2016, original scientific article

Abstract: A sensitive, specific and rapid liquid chromatography - tandem mass spectrometry method was developed and validated for the determination of candesartan in human plasma. Analyte was separated from endogenous components present in plasma by solid phase extraction. Chromatographic separation was performed on Gemini C18 analytical column using mobile phase acetonitrile – 5 mM ammonium formate pH 2 (90:10, v/v) at flow rate of 0.3 mL/min. For detection, tandem mass spectrometry in SRM mode with positive electrospray ionization was used. The mass transitions m/z 441.1 > 263.1 and 445.1 > 267.1 were used to determine candesartan by using candesartan-d4 as an internal standard. After development, the method was validated according to the requirements of EMA regulatory guidelines in the concentration range 1 - 400 ng/ml in human plasma. Limit of quantification (LLOQ) was 1 ng/ml. The developed and validated method proved to be very fast and reproducible and was therefore successfully implemented in pharmacokinetic and bioequivalence studies with large number of study samples.
Keywords: candesartan, liquid chromatography, tandem mass spectrometry, human plasma
Published in DKUM: 17.08.2017; Views: 1395; Downloads: 376
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Comparison of methods for determination of polyphenols in wine by HPLC-UV/VIS, LC/MS/MS and spectrophotometry
Vesna Mila Meden, Matija Strlič, Drago Kočar, 2009, original scientific article

Abstract: Phenolic antioxidants are usually grouped into flavonoids and non-flavonoids, according to their structure. With regard to the tannic character, phenolic antioxidants are further subdivided to tannic phenols and non-tannic phenols. Collectively, these compounds contribute to the high antioxidant capacity of wine. In this work, we compare determination of gallic acid, catechin, epicatechin, resveratrol, quercetin, dihydrobenzoic acid, sinapic acid, vanillic acid, caffeic acid, chlorogenic acid, ferullic acid, ellagic acid, p-coumaric acid and caftaric acid in 141 wine samples using two liquid chromatographic methods and detection systems, i.e. with UV detection and mass-spectrometric detection. In addition, we applied the conventional Folin-Ciocalteu spectrophotometric method for determination of the total phenolic content in wine samples and compared the results with those obtained using the chromatographic methods. Despite satisfactory correlations statistically significant differences between HPLC-UV/VIS and LC/MS/MS were established, which could be related to coelution not detectable with UV/VIS detectors. The correlations between results of the spectrophotometric method and sum of LC/MS/MS determinations are not satisfactory and are different for white, red, and rosé wines.
Keywords: food analysis, wine, antioxidants, chromatography
Published in DKUM: 17.08.2017; Views: 2031; Downloads: 153
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Extraction and separation of active compounds by supercritical fluids extraction and preparative supercritical chromatography
Alejandro Bartolome Ortega, 2017, doctoral dissertation

Abstract: This doctoral dissertation is focused on the benefits of supercritical fluids technology in several industry processes. Although, supercritical CO2 is currently the most employed supercritical fluid at laboratory scale, its presence in the industry field is still limited, due to the necessity of high investment costs. Despite that fact, operations with supercritical CO2 are cheap, environmentally friendly and simple, which make it an excellent alternative to organic compounds. Extraction and separation of highly pure active compounds, such as xanthohumol or beta-sitosterol, are demanded for pharmaceutical or food industries, which create an excellent opportunity for supercritical CO2 operations, since they are solvent free. This manuscript is divided into three different parts. In the first part, conventional extraction processes and supercritical fluid process are theoretically compared and supercritical fluid extraction from saw palmetto berries is presented. In the second part, conventional chromatographic techniques and supercritical fluid chromatography are theoretically compared and separation of xanthohumol from hop extracts by supercritical fluid chromatography is presented. In the last part, different encapsulation and emulsification processes are listed and defined. These processes are very important for food and pharmaceutical companies, since several active compounds are not water soluble which create the necessity of different formulations in order to be solved in an appropriate media. Regarding the experimental part, extractions from saw palmetto berries were performed at various pressures and temperatures, which were higher than the ones that were applied in previous studies, in order to estimate and calculate different parameters (solubility, extraction kinetic curves, composition,…), and to compare different studies. Separation of xanthohumol was carried out in a homemade supercritical chromatography, which manageable variables were temperature, pressure, mass flow-rate, modifier, and stationary phase. The results were compared with those ones which were obtained using conventional techniques, in order to prove the suitability and the improvement of this technique against others tecniques.
Keywords: supercritical CO2, supercritical fluid extraction, supercritical fluid chromatography, xanthohumol, saw palmetto berries, Beta-Sitosterol, encapsulation
Published in DKUM: 13.07.2017; Views: 2015; Downloads: 243
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Gut microbiota patterns associated with colonization of different clostridium difficile ribotypes
Jure Škraban, Sašo Džeroski, Bernard Ženko, Domen Mongus, Simon Gangl, Maja Rupnik, 2013, original scientific article

Abstract: Abstract Introduction Materials and Methods Results Discussion Supporting Information Acknowledgments Author Contributions References Reader Comments (0) Figures Abstract C. difficile infection is associated with disturbed gut microbiota and changes in relative frequencies and abundance of individual bacterial taxons have been described. In this study we have analysed bacterial, fungal and archaeal microbiota by denaturing high pressure liquid chromatography (DHPLC) and with machine learning methods in 208 faecal samplesfrom healthy volunteers and in routine samples with requested C. difficile testing. The latter were further divided according to stool consistency, C. difficile presence or absence and C. difficile ribotype (027 or non-027). Lower microbiota diversity was a common trait of all routine samples and not necessarily connected only to C. difficile colonisation. Differences between the healthy donors and C. difficile positive routine samples were detected in bacterial, fungal and archaeal components. Bifidobacterium longum was the single most important species associated with C. difficile negative samples. However, by machine learning approaches we haveidentified patterns of microbiota composition predictive for C. difficile colonization. Those patterns also differed between samples with C. difficile ribotype 027 and other C. difficile ribotypes. The results indicate that not only the presence of a single species/group is important but that certain combinations of gut microbes are associated with C. difficile carriage and that some ribotypes (027) might be associated with more disturbed microbiota than the others.
Keywords: microbiota, clostridium difficile, chromatography
Published in DKUM: 19.06.2017; Views: 1327; Downloads: 372
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Supercritical fluid chromatography and scale up study
Miha Oman, Petra Kotnik, Mojca Škerget, Željko Knez, 2014, original scientific article

Abstract: The influence of process parameters on supercritical fluid chromatography (SFC) and scale-up on to the preparative scale was investigated. In this scope, dependency of pressure, temperature, type and concentration of modifier, and type of stationary phase on the separation were examined separately. Experiments were performed on silica stationary phases in the range of pressures from 100 bar to 250 bar and temperatures from 30°C to 65°C, with use of ethanol and methanol as modifier. Results obtained on analytical scale were used for scale up on preparative (to production) scale. The aim of this study is presentation of the state-of-the-art of SFC through separate effects of process parameters on the separation and investigation of development, benefits and drawbacks of scaling-up process of the SFC.
Keywords: supercritical fluids, supercritical fluid chromatograpy, chromatography, scale up study, SFC
Published in DKUM: 21.12.2015; Views: 1521; Downloads: 153
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Determination of major phenolic acids, phenolic diterpenes and triterpenes in Rosemary (Rosmarinus Officinalis L.) by gas chromatography and mass spectrometry
Maša Islamčević Razboršek, Darinka Brodnjak-Vončina, Valter Doleček, Ernest Vončina, 2007, original scientific article

Abstract: A gas chromatographic-mass spectrometric (GC-MS) method for the simultaneous identification and quantification of seven major phenolic and terpenic compounds in Rosmarinus officinalis L. was developed. The compounds were identified as trimethylsilyl (TMS) derivatives of phenolic acids (caffeic and rosmarinic acid), phenolic diterpene (carnosic acid), and pentacyclic triterpenes (ursolic, oleanolic, betulinic acid and betulin). These compounds have been identified by retention time and comparison of mass spectra. The procedure involves ultrasonic extraction using solvent mixture of tetrahydrofuran and ethanol. Extracts were fractionated by size exclusion chromatography (SEC) after purifying on graphitised carbon. The fraction with phenolic and terpenic compounds was derivatised prior to GC-MS analysis using N-methyl-N-trimethylsilyl trifluoroacetamide (MSTFA) as a derivatisation reagent. The derivatisation process was optimized regarding temperature and reaction time. The linearity of the method was tested in concentration range 4-25 mg L$^{–1}$. The correlation coefficients ($r^2$) were in the range of 0.997 to 0.999. The average recoveries for all compounds ranged from 80 to 82%. The GC-MS technique is specific and sensitive, and can be used for simultaneous identification and determination of a wide range of phenolic and terpenic compounds in different plants even at trace levels.
Keywords: Rosmarinus officinalis, diterpenes, triterpenes, size exclusion chromatography, gas chromatography, mass spectrometry
Published in DKUM: 21.12.2015; Views: 1730; Downloads: 197
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