Countercurrent chromatography in analytical chemistry (IUPAC technical report)

© 2009 IUPACCountercurrent chromatography (CCC) is a generic term covering all forms of liquid-liquid chromatography that use a support-free liquid stationary phase held in place by a simple centrifugal or complex centrifugal force field. Biphasic liquid systems are used with one liquid phase being the stationary phase and the other being the mobile phase. Although initiated almost 30 years ago, CCC lacked reliable columns. This is changing now, and the newly designed centrifuges appearing on the market make excellent CCC columns. This review focuses on the advantages of a liquid stationary phase and addresses the chromatographic theory of CCC. The main difference with classical liquid chromatography (LC) is the variable volume of the stationary phase. There are mainly two different ways to obtain a liquid stationary phase using centrifugal forces, the hydrostatic way and the hydrodynamic way. These two kinds of CCC columns are described and compared. The reported applications of CCC in analytical chemistry and comparison with other separation and enrichment methods show that the technique can be successfully used in the analysis of plants and other natural products, for the separation of biochemicals and pharmaceuticals, for the separation of alkaloids from medical herbs, in food analysis, etc. On the basis of the studies of the last two decades, recommendations are also given for the application of CCC in trace inorganic analysis and in radioanalytical chemistry

Novel User-Friendly Application for MRI Segmentation of Brain Resection following Epilepsy Surgery

Delineation of resected brain cavities on magnetic resonance images (MRIs) of epilepsy surgery patients is essential for neuroimaging/neurophysiology studies investigating biomarkers of the epileptogenic zone. The gold standard to delineate the resection on MRI remains manual slice-by-slice tracing by experts. Here, we proposed and validated a semiautomated MRI segmentation pipeline, generating an accurate model of the resection and its anatomical labeling, and developed a graphical user interface (GUI) for user-friendly usage. We retrieved pre- and postoperative MRIs from 35 patients who had focal epilepsy surgery, implemented a region-growing algorithm to delineate the resection on postoperative MRIs and tested its performance while varying different tuning parameters. Similarity between our output and hand-drawn gold standards was evaluated via dice similarity coefficient (DSC; range: 0–1). Additionally, the best segmentation pipeline was trained to provide an automated anatomical report of the resection (based on presurgical brain atlas). We found that the best-performing set of parameters presented DSC of 0.83 (0.72–0.85), high robustness to seed-selection variability and anatomical accuracy of 90% to the clinical postoperative MRI report. We presented a novel user-friendly open-source GUI that implements a semiautomated segmentation pipeline specifically optimized to generate resection models and their anatomical reports from epilepsy surgery patients, while minimizing user interaction

Equity valuation Coca-Cola company

This dissertation aims to determine the fair value per share of Coca-Cola Company (KO), one of the leaders in the Soft Drink industry. The main purpose of this dissertation is to provide to potential investors an overview of KO and an investment recommendation. The thesis begin with a theoretical overview of the economic doctrine, to examine the various valuation tools and then decided to use two valuation approaches: discounted cash flows and valuation through multiples that helped to smooth the price, enriching the valuation with considerations derived from the Peer choices, operating in related markets. The sensitivity analysis was then carried out to understand how the variation of two critical variables, WACC and Growth Rate, within the DCF, can affect the stock price. The final recommendation is BUY, coherent with an expected increase in the share price by approximately 16%; a recommendation that has been shown to be consistent with the results of the Coca-Cola Equity report published by Trefis.Esta dissertação visa determinar o valor justo por acção da Coca-Cola Company (KO), um dos líderes na indústria dos refrigerantes. O principal objectivo desta dissertação é fornecer aos potenciais investidores uma visão geral da KO e uma recomendação de investimento. A tese começa com uma visão teórica da doutrina económica, para examinar as várias ferramentas de avaliação e depois decide utilizar duas abordagens de avaliação: fluxos de caixa descontados e avaliação através de múltiplos que ajudaram a suavizar o preço, enriquecendo a avaliação com considerações derivadas das escolhas dos pares, operando em mercados relacionados. A análise de sensibilidade foi então realizada para compreender como a variação de duas variáveis críticas, WACC e Taxa de Crescimento, dentro do DCF, pode afectar o preço das acções. A recomendação final é BUY, coerente com um aumento esperado do preço das acções em cerca de 16%; uma recomendação que se tem mostrado consistente com os resultados do relatório da Coca-Cola Equity publicado pela Trefi

Polyphenols in countercurrent chromatography. An example of large scale separation

Polyphenols are sometimes difficult to separate in classical liquid chromatography. Countercurrent chromatography uses a biphasic liquid system to separate the components of a mixture. A centrifugal field allows to use a liquid stationary phase in an open tube. The phase density difference and the centrifugal field are the only parameters allowing the equilibrium between the two liquid phases. The big advantage of the technique in preparative separation is the dual- mode capability of CCC. The role of the phases can be switched during a run. The mobile phase becomes stationary and vice versa. Then no injected material can be left in the machine. The large scale separations of a flavonoid mixture and two tannin samples are described: choice of the biphasic liquid system, analytical study, scaling-up, injection protocol, two step separation in case of dual-mode use. It was possible to inject 26 g of a tannin sample in one run