Search results for "Spectroscopy"
showing 10 items of 10293 documents
Recent trends in liquid chromatography-tandem mass spectrometry to determine pesticides and their metabolites in food
2007
Abstract The applications of liquid chromatography-mass spectrometry (LC-MS) have exploded in innumerable analytical fields, including pesticide-residue determination. There is no doubt that LC-MS is currently competing with gas chromatography (GC)-MS for the status of ‘reference’ analytical technique to determine pesticide residues and that its ever-increasing application is bound to the evolution of modern instruments and their growing performance qualities. We highlight the large number and variety of pesticides that can be readily determined using such instruments, the respective merits of the different mass analyzers, and the improvements brought about by tandem MS (MS 2 ). We also dis…
Infrared biospectroscopy for a fast qualitative evaluation of sample preparation in metabolomics.
2014
Liquid chromatography-mass spectrometry (LC-MS) has been increasingly used in biomedicine to study the dynamic metabolomic responses of biological systems under different physiological or pathological conditions. To obtain an integrated snapshot of the system, metabolomic methods in biomedicine typically analyze biofluids (e.g. plasma) that require clean-up before being injected into LC-MS systems. However, high resolution LC-MS is costly in terms of resources required for sample and data analysis and care must be taken to prevent chemical (e.g. ion suppression) or statistical artifacts. Because of that, the effect of sample preparation on the metabolomic profile during metabolomic method d…
MALDI-TOF characterization of macromonomers
1996
Methacryloyl endfunctionalized oligostyrene macromonomers were characterized by matrix assisted laser desorption ionization/time of flight (MALDI-TOF) spectroscopy and by isocratic and gradient high performance liquid chromatography (HPLC). The molar mass distribution derived by the different techniques coincide for the investigated oligomers. Mixing experiments revealed that the MALDI-TOF peak areas do not necessarily represent the mixing ratio of the components. Combination of gradient HPLC and MALDI-TOF has resolved the chemical composition of the coupling products formed by reaction of the living anion with oxygen.
Pressurized liquid extraction of organic contaminants in environmental and food samples
2015
Pressurized liquid extraction (PLE) is an automated technique that uses elevated temperature and pressure to achieve exhaustive extraction from solid matrices, so reducing solvent consumption and enhancing sample throughput when compared with traditional procedures. Hence, it can be considered an environment-friendly technique, generating small volumes of waste and reducing costs and time. This review focuses on application of this green technique to the analysis of organic contaminants in food and environmental matrices for monitoring purposes. We examine fundamentals and key aspects of the development of a PLE method, including pressurized hot-water extraction, together with some relevant…
Resolution assessment and performance of several organic modifiers in hybrid micellar liquid chromatography
2001
The performance of four criteria that measure the elementary resolution (modified selectivity, modified RS, peak purity, and orthogonal valley-to-peak ratio) was critically assessed using as global resolution function, the product of elementary measurements. The peak purities and valley-to-peak criteria yielded the best description of the overall separation according to the shape of the resolution surfaces compared to the peak arrangements in the chromatograms, the capability of defining unambiguously the composition regions of complete resolution, and the resolution achieved in the predicted optimums. Peak purities were used to compare the effect of five organic modifiers (1-propanol, 1-bu…
Protocol to compare column performance applied to hydrophilic interaction liquid chromatography
2019
Abstract The lack of retention of highly polar solutes in liquid chromatography with reversed phase columns (RPLC) can be solved through the use of the hydrophilic interaction liquid chromatographic (HILIC) mode. Due to the complexity of the separation mechanisms in HILIC and the different factors that may have significant influence, the selection of the appropriate stationary phase plays a fundamental role in the development of analytical procedures to obtain good performance. In this work, the chromatographic performance of bare silica and six polar stationary phases with different functionalized groups (with neutral, cationic, anionic and zwitterionic character) are investigated. The beh…
H-point standard additions method for resolution of overlapped chromatographic peaks with a conventional fluorescence detector. Determination of phen…
1996
The H-Point Standard Additions Method (HPSAM) is proposed in order to resolve overlapping peaks in liquid chromatography by using a conventional fluorescence detector. The method uses as analytical signals the heights or the areas obtained at two previously selected emission wavelengths, and good results are obtained for highly overlapping peaks with highly overlapping fluorescence spectra. The principal benefits of the method are the ease of finding the required wavelengths, its insensitivity to changes in the retention time of the peak from one injection to another, and the possibility of using it in highly or only partially overlapping peaks. We have applied the method to the determinati…
Global treatment of chromatographic data with MICHROM
1997
Abstract The program MICHROM for the general treatment of chromatographic data is presented. MICHROM takes part in all the stages of the analytical process. It allows determination of dead time, smoothing of chromatograms, measurement of peak parameters, fitting of skewed peaks, and deconvolution of overlapped peaks. Tools for the experimental design, optimization of the mobile phase composition to resolve a mixture of analytes, and simulation of chromatograms in several experimental conditions, are implemented. Routines for the graphical representation of chromatograms, resolution surfaces, contour maps, management of data series, optimization and regression analysis, are also included. Th…
Models and objective functions for the optimisation of selectivity in reversed-phase liquid chromatography.
2006
Interpretive methodologies are the most efficient tools for finding the optimal conditions in chromatography. These methodologies are supported by models or algorithms able to infer the system behaviour upon changes in the experimental factors. Once the models are built with data obtained from sets of carefully designed experiments, molecular modelling or other approaches, they can be applied to predict the performance of new conditions. The different elements involved in these methodologies, for both isocratic and gradient elution, are given. Special attention is devoted to the description of retention, owing to its major impact on the prediction of chromatographic resolution. Several mode…
Evaluation of several global resolution functions for liquid chromatography
1999
Abstract An interpretative approach, that makes use of the overlapped fraction of each chromatographic peak as elementary resolution criterion, was applied to the separation of mixtures of compounds. The elementary resolution measurements for all peaks in the chromatogram were reduced to a single numerical value using several functions: normalised by the mean resolution product, unnormalised product, geometrical mean of the unnormalised product, and worst elementary resolution value. The descriptive capability of these reduction functions was evaluated through the observation of global resolution diagrams and the change in the shape of the chromatograms in the selected factor space. michrom…