Application of chemometry for optimization of liquid chromatographic parameters

Liquid chromatography is one of the most common separation techniques. Optimization of the experimental conditions is a complicated process due to the large number of the variables, which must be simultaneously treated. This mini review summarizes some of the chemometric approaches used in the literature to separate mixtures

Applied mathematical modelling with new parameters and applications to some real life problems

Some Epidemic models with fractional derivatives were proved to be well-defined, well-posed and more accurate [34, 51, 116], compared to models with the conventional derivative. An Ebola epidemic model with non-linear transmission is fully analyzed. The model is expressed with the conventional time derivative with a new parameter included, which happens to be fractional (that derivative is called the derivative). We proved that the model is well-de ned and well-posed. Moreover, conditions for boundedness and dissipativity of the trajectories are established. Exploiting the generalized Routh-Hurwitz Criteria, existence and stability analysis of equilibrium points for the Ebola model are performed to show that they are strongly dependent on the non-linear transmission. In particular, conditions for existence and stability of a unique endemic equilibrium to the Ebola system are given. Numerical simulations are provided for particular expressions of the non-linear transmission, with model's parameters taking di erent values. The resulting simulations are in concordance with the usual threshold behavior. The results obtained here may be signi cant for the ght and prevention against Ebola haemorrhagic fever that has so far exterminated hundreds of families and is still a ecting many people in West-Africa and other parts of the world. The full comprehension and handling of the phenomenon of shattering, sometime happening during the process of polymer chain degradation [129, 142], remains unsolved when using the traditional evolution equations describing the degradation. This traditional model has been proved to be very hard to handle as it involves evolution of two intertwined quantities. Moreover, the explicit form of its solution is, in general, impossible to obtain. We explore the possibility of generalizing evolution equation modeling the polymer chain degradation and analyze the model with the conventional time derivative with a new parameter. We consider the general case where the breakup rate depends on the size of the chain breaking up. In the process, the alternative version of Sumudu integral transform is used to provide an explicit form of the general solution representing the evolution of polymer sizes distribution. In particular, we show that this evolution exhibits existence of complex periodic properties due to the presence of cosine and sine functions governing the solutions. Numerical simulations are performed for some particular cases and prove that the system describing the polymer chain degradation contains complex and simple harmonic poles whose e ects are given by these functions or a combination of them. This result may be crucial in the ongoing research to better handle and explain the phenomenon of shattering. Lastly, it has become a conjecture that power series like Mittag-Le er functions and their variants naturally govern solutions to most of generalized fractional evolution models such as kinetic, di usion or relaxation equations. The question is to say whether or not this is always true! Whence, three generalized evolution equations with an additional fractional parameter are solved analytically with conventional techniques. These are processes related to stationary state system, relaxation and di usion. In the analysis, we exploit the Sumudu transform to show that investigation on the stationary state system leads to results of invariability. However, unlike other models, the generalized di usion and relaxation models are proven not to be governed by Mittag-Le er functions or any of their variants, but rather by a parameterized exponential function, new in the literature, more accurate and easier to handle. Graphical representations are performed and also show how that parameter, called ; can be used to control the stationarity of such generalized models.Mathematical SciencesPh. D. (Applied Mathematics

Application of Aboodh Transform Iterative Method for Solving Time – Fractional Partial Differential Equations

In this paper, the Aboodh transform iterative method is used to obtain approximate analytical solution of time-fractional partial differential equations. The fractional derivative are considered in Caputo sense, this method is a combination of the Aboodh transform and the new iterative method. Illustrative examples are considered and the comparison between the exact and approximate solutions are presented for different values of alphas. Also, the surface plots are provided in order to comprehend the effect of the fractional order. The major advantage of this method is the reduced computational effort and complexity without involving the tedious calculations of Adomian polynomials. In general, the method is efficient, precise, easy to implement and yield good results

Validation of an Innovative Groundwater Contaminant Flux Measurement Method

The ability to measure groundwater contaminant flux is increasingly being recognized as crucial in order to prioritize contaminated site cleanups, estimate the efficiency of remediation technologies, measure rates of natural attenuation, and apply proper source terms to model groundwater contaminant transport. An innovative mass flux measurement method using horizontal flow treatment wells (HFTWs) was developed recently to compensate for the disadvantages of other flux measurement methods that are being used. Flux measurement methods can be categorized as either point methods or integral methods. As the name suggests, point methods measure flux at a specific point or points in the subsurface. To increase confidence in the accuracy of the measurement, it is necessary to increase the number of points (and therefore, the cost) of the sampling network. Integral methods avoid this disadvantage by using pumping wells to interrogate large volumes of the subsurface. Unfortunately, integral methods are expensive because they require that large volumes of contaminated water be extracted and managed. HFTWs combine the advantages of each of the two approaches described above; that is, it is an integral technique that samples a large volume of the subsurface while not requiring extraction of contaminated water from the subsurface. In this study, the accuracy of the HFTW flux measurement method was quantified by applying the method in an artificial aquifer, where the flux being measured was known. Two HFTW approaches, the multi-dipole approach and the tracer test approach, were compared to each other, as well as being compared to the transect method of measuring flux, which is the conventionally used point method. Results found that the transect and HFTW tracer test approaches provided reasonably accurate measures of flux (within 50% and 44% respectively) in the artificial aquifer, while the multi-dipole approach was too sensitive to small hydraulic head measurement errors to be useful. A comparison of the costs of applying the different methods at a generic site showed that the HFTW method had significant cost advantages. This study also compared other advantages and disadvantages of the various flux measurement methods, concluding that depending on conditions at a site, one or the other method may be most advantageous for application

Liquid phase microextraction of hallucinogenic compounds from human urine samples based on single hollow fibre followed by chromatographic determination

A dissertation submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Master of Science. University of the Witwatersrand, Johannesburg, March 2016A liquid phase microextraction based on single hollow fibre followed by liquid chromatographic determination was developed for the extraction and quantification of the hallucinogenic muscimol and its two precursors, tryptophan and tryptamine from urine samples. A multivariate design of experiment was used in which a half fractional factorial approach was applied to screen six potential factors (donor phase pH, acceptor phase concentration, supported liquid membrane composition, stirring rate, extraction time and salt content) for their extent of vitality on the extraction of muscimol, tryptophan and tryptamine using the developed method. Four factors were identified as essential for an enhanced enrichment of each of the three research analytes from diluted urine samples. The paired vital factors were then optimized using central composite designs where empirical quadratic response models were used to visualize the response surface through contour plots, surface plots and optimization plots of response output. When the muscimol-based optimum factor levels were applied for the simultaneous extraction of the three research analytes, a composite desirability of 0.687 was obtained implying that the set conditions were ideal for a combined extraction of the analytes from the donor phase into the acceptor phase across a supported liquid membrane impregnated with a carrier molecule. This was an acceptable result considering that only the optimized muscimol factor levels were set as universal factor values. Muscimol was the analyte of interest in this research. The composite desirability value was predicted by setting the extraction conditions to 20% (w/w) di-(2-ethylhexyl) phosphoric acid (DEHPA) in dihexyl ether (DHE) supported on the walls of a hollow fibre into a 200 mM HCl acceptor phase inside the hollow fibre from a 20% (v/v) diluted urine donor phase spiked in the 0.1 – 10 μg mL-1 analyte concentration range maintained at pH 4 and stirred at 800 rpm for 60 mins. Experimentally, average enrichments of 4.1, 19.7 and 24.1 were obtained for muscimol, tryptophan and tryptamine, respectively. iv The complexity of urine and the anionic nature of the carrier molecule embedded on the supported liquid membrane resulted in interfering peaks that could not be completely resolved from the analyte peaks. Thus matrix-based calibration curves were used to address matrix effects. Various statistical approaches were used to validate suitability of the developed method for its potential use in quantifying muscimol and its precursors from urine samples. These validation measures were used as a way of determining the method’s ability to maintain the extraction process at equilibrium over a specific range of analyte concentrations over a period of analyte existence in a urine sample. The r² values of the matrix-based linear regression prediction models ranged from 0.9933 to 0.9986. The linearity of the regression line of the matrixbased calibration for each analyte was directly linked to the analyte enrichment repeatability. Simultaneous analyte enrichment repeatability over a 0.1 – 10 μg mL-1 analyte spiking concentration ranged from an RSD value of 8.3% to 13.1%. Limits of detection were 0.021 μg mLˉ¹, 0.061 μg mL-1 and 0.005 μg mL-1 for muscimol, tryptophan and tryptamine, respectively. Other validation parameters that were considered included specificity (and selectivity), accuracy, robustness, extraction range and system suitability. The accuracy of the developed method was reported as the reproducibility of enrichment factor values over six spiking concentrations used in constructing matrix-based calibration curves. System suitability was limited to an HPLC-UV approach. Method suitability was addressed through a comparative summary in which the LOD, LOQ and r² values for the developed method were compared to other methods that have been used to extract muscimol from urine samples. The relevance or acceptability of the enrichment factor values obtained for the extraction of the three analytes was achieved by comparison with enrichment factor values of several compounds with similar polarity that have been extracted from urine samples using carrier-mediated hollow fibre liquid phase microextraction.GR201

Stability analysis of a second-order difference scheme for the time-fractional mixed sub-diffusion and diffusion-wave equation

This study investigates a class of initial-boundary value problems pertaining to the time-fractional mixed sub-diffusion and diffusion-wave equation (SDDWE). To facilitate the development of a numerical method and analysis, the original problem is transformed into a new integro-differential model which includes the Caputo derivatives and the Riemann-Liouville fractional integrals with orders belonging to (0,1). By providing an a priori estimate of the solution, we have established the existence and uniqueness of a numerical solution for the problem. We propose a second-order method to approximate the fractional Riemann-Liouville integral and employ an L2 type formula to approximate the Caputo derivative. This results in a method with a temporal accuracy of second-order for approximating the considered model. The proof of the unconditional stability of the proposed difference scheme is established. Moreover, we demonstrate the proposed method's potential to construct and analyze a second-order L2-type numerical scheme for a broader class of the time-fractional mixed SDDWEs with multi-term time-fractional derivatives. Numerical results are presented to assess the accuracy of the method and validate the theoretical findings

3d food printing: study and applications to produce innovative food products.

La stampa 3D degli alimenti rappresenta una tecnologia innovativa ed emergente capace di costruire un oggetto tridimensionale partendo da un modello CAD creato su software di disegno grafico. Durante gli ultimi anni molti studi hanno dimostrato come questa tecnologia sia stata applicata per la produzione di alimenti nuovi. L’obiettivo principale di questa tesi è stato l’approfondimento e il miglioramento della tecnologia di stampa 3D nel settore alimentare contribuendo alla creazione di alimenti dalle proprietà mai esplorate prima. Dopo un’analisi dell’evoluzione temporale della tecnologia di stampa 3D nel settore alimentare, una varietà di altri aspetti sono stati studiati, tra cui la capacità di creare e modificare alimenti dalle nuove texture attraverso la progettazione di nuovi design, inoltre è stata oggetto di studio la stampa 3D ad alta velocità, tema interessante dal punto di vista dell’applicazione in campo industriale. Gli studi si sono focalizzati sull’utilizzo di due diverse matrici di stampa: impasto a base di cereali e gel a base d’amido, stampando strutture geometriche (cubi, parallelepipedi) e design ispirati alla natura (tessuti interni delle mele). La tesi è strutturata in 8 capitoli: una breve introduzione (capitolo 1), obiettivi e linee di ricerca (capitolo 2) e altri cinque capitoli corrispondenti alle 5 pubblicazioni su riviste internazionali; Drawing the scientific landscape of 3D Food Printing. Maps and interpretation of the global information in the first 13 years of detailed experiments, from 2007 to 2020’(capitolo 3) and ‘Rheological properties, dispensing force and printing fidelity of starchy-gels modulated by concentration, temperature and resting time’ (capitolo 4). I capitoli 5 e 6 sono dedicati alla creazione di alimenti stampati in 3D con proprietà meccaniche desiderate e personalizzabili: Programmable texture properties of cereal-based snack mediated by 3D printing technology’ (capitolo 5), ‘Extending 3D food printing application. Apple tissues microstructure as CAD model to create innovative cereal-based snacks’ (capitolo 6). Il capitolo 7 si è focalizzato sulla stampa 3D ad alta velocità: ‘Extending the 3D food printing tests at high speed. Material deposition and effect of non-printing movements on the final quality of printed structures’. E infine il capitolo 8 racchiude le conclusioni e alter discussioni generali riguardanti la tesi.3D printing (3DP) represents an innovative and emerging technology aiming to build three-dimensional objects starting from the computer-aided model. During last years main studies showed the application of this technology to produce innovative foods. The main aim of this research was the better understanding and the implementation of 3D Printing in the food sector aiming to contribute to the creation of food with unprecedented properties. After an analysis on the temporal evolution of 3D Food Printing (3DFP) in scientific field, a variety of relevant aspects have been studied: the capability of modifying the texture properties of the end products by means of accurate design of the digital models and the printing at high speed that could open for a more practical application at industrial level. Moreover, the studies have focused on two different matrix: cereals based and starchy gels, printing geometric structures (cube, parallelepiped) and design inspired by nature (apple tissue). The thesis is structured in 8 chapters: a brief introduction (chapter 1), objects and outlines of research (chapter 2) and the other sections consists of five published papers in international peer reviewed journals ‘Drawing the scientific landscape of 3D Food Printing. Maps and interpretation of the global information in the first 13 years of detailed experiments, from 2007 to 2020’(chapter 3); ‘Rheological properties, dispensing force and printing fidelity of starchy-gels modulated by concentration, temperature and resting time’ (chapter 4). The chapters 5 and 6 has been dedicated to the creation of 3D-printed food with desired and programmable mechanical properties: ‘Programmable texture properties of cereal-based snack mediated by 3D printing technology’ (chapter 5), ‘Extending 3D food printing application. Apple tissues microstructure as CAD model to create innovative cereal-based snacks’ (chapter 6). Chapter 7 focused on speed up of 3DFP: ‘Extending the 3D food printing tests at high speed. Material deposition and effect of non-printing movements on the final quality of printed structures’. Finally chapter 8 contains the conclusions and some general discussion of the thesis

Quality-by-design in pharmaceutical development: From current perspectives to practical applications

Current pharmaceutical research directions tend to follow a systematic approach in the field of applied research and development. The concept of quality-by-design (QbD) has been the focus of the current progress of pharmaceutical sciences. It is based on, but not limited, to risk assessment, design of experiments and other computational methods and process analytical technology. These tools offer a well-organized methodology, both to identify and analyse the hazards that should be handled as critical, and are therefore applicable in the control strategy. Once implemented, the QbD approach will augment the comprehension of experts concerning the developed analytical technique or manufacturing process. The main activities are oriented towards the identification of the quality target product profiles, along with the critical quality attributes, the risk management of these and their analysis through in silico aided methods. This review aims to offer an overview of the current standpoints and general applications of QbD methods in pharmaceutical development