Search results for "Resolution"
showing 10 items of 1928 documents
A rapid and sensitive method for the control of selected regulated and emerging mycotoxins in beer
2018
A fast method using automated online solid-phase extraction (SPE) coupled to liquid-chromatography/high resolution mass spectrometric (LC-HRMS) detection for the determination of 12 mycotoxins in beer was developed and fully validated according to the performance criteria set in the European Union (EU) guidelines. Mycotoxin detection was achieved by full-scan HRMS with electrospray ionisation in positive ion mode within 13 min. No significant matrix interferences were observed. The lowest limits of detection (LODs) were achieved for emerging mycotoxins (beauvericin and enniatins) and ochratoxin A at levels between 0.01 and 0.02 μg/l, while the overall LODs were in the range of 0.01-0.30 μg…
Peak deconvolution in one-dimensional chromatography using a two-way data approach.
2002
A deconvolution methodology for overlapped chromatographic signals is proposed. Several single-wavelength chromatograms of binary mixtures, obtained in different runs at diverse concentration ratios of the individual components, were simultaneously processed (multi-batch approach), after being arranged as two-way data. The chromatograms were modelled as linear combinations of forced peak profiles according to a polynomially modified Gaussian equation. The fitting was performed with a previously reported hybrid genetic algorithm with local search, leaving all model parameters free. The approach yielded more accurate solutions than those found when each experimental chromatogram was fitted in…
Prediction of peak shape as a function of retention in reversed-phase liquid chromatography
2004
Optimisation of the resolution of multicomponent samples in HPLC is usually carried out by changing the elution conditions and considering the variation in retention of the analytes, to which a standard peak shape is assigned. However, the change in peak shape with the composition of the mobile phase can ruin the optimisation process, yielding unexpected overlaps in the experimental chromatograms for the predicted optimum, especially for complex mixtures. The possibility of modelling peak shape, in addition to peak position, is therefore attractive. A simple modified-Gaussian model with a parabolic variance, which is a function of conventional experimental parameters: retention time (tR), p…
Levels in the interpretive optimisation of selectivity in high-performance liquid chromatography: a magical mystery tour.
2006
Interpretive approaches for selectivity optimisation, which are those supported by retention models, are able to exploit efficiently the capabilities of the chromatographic system. The resolution of a mixture is usually faced in a first trial by looking for a unique experimental condition, able to resolve all compounds in the sample. If this is not possible, the problem can be outlined with less ambitious aims, focusing on only some compounds. In an extreme case, a single analyte can be individually optimised. Current strategies that give answer to the different goals pursued in the analysis, which are classified as total, partial and specific, are reviewed. Optimisation oriented to deconvo…
Filter-based infrared detectors for high temperature size exclusion chromatography analysis of polyolefins: calibration with a small number of standa…
2012
Infrared detection has been shown to be very appropriate for high temperature analysis of polyolefins. After some early reports in which dispersive or single-band filter-based detectors were applied, Fourier transform detectors have been described for this application, in order to improve the method sensitivity. Modern simple filter-based detectors prove, however, comparable sensitivity while providing a number of practical advantages when coupled to chromatographic systems: reduced cell volume, simplified hardware, continuous generation of absorbance chromatograms, as well as simpler data collection and processing. A practical method for calibration, using multiple-band signals obtained wi…
Column technology in liquid chromatography
2017
This chapter deals with the most important part of the liquid chromatography (LC) system: the column enabling the efficient and fast resolution of complex mixtures. It is divided into seven sections under the overall aspects of manufacture, operation, and evaluation of analytical columns for the user. The first three sections highlight the column design and hardware, followed by a thorough treatment of the properties of microparticulate silica adsorbents as packing material, stationary phases performed by surface functionalization, and the column filling process. Then, the implementation of the column into the LC system is discussed, leading into chromatographic column testing as a C18-bond…
Modelling of retention behaviour of solutes in micellar liquid chromatography
1997
In micellar liquid chromatography (MLC), the resolution for a given multi-component mixture can be optimized by changing several variables, such as the concentrations of surfactant and organic modifier, the pH and temperature. However, this advantage can only be fully exploited with the development of mathematical models that describe the retention and the separation mechanisms. Several reports have appeared recently on the possibilities of accurately predicting the solute retention in MLC. Although the retention and selectivity may strongly change with varying concentrations of surfactant, organic modifier and/or pH, the observed changes are very regular, and are well described by simple m…
Interpretive optimisation of organic solvent content and flow-rate in the separation of β-blockers with a Chromolith RP-18e column
2009
The chromatographic performance of a Chromolith RP-18e column was comprehensively examined for a group of basic drugs (beta-blockers), eluted with isocratic ACN-water mixtures at increasing flow-rate up to 6 mL/min. As the flow-rate increases at fixed mobile phase composition, peak distribution (selectivity) is maintained, but the relative peak widths increase. This reduces the resolution below satisfactory values for closely eluting compounds. With the monolithic column, flow-rate becomes thus an important factor to be optimised, in addition to the mobile phase composition. Since, theoretically, retention factors (k) are independent of the flow-rate, the classical quadratic model relating …
Net analyte signal as a deconvolution-oriented resolution criterion in the optimisation of chromatographic techniques
2003
The performance of two multivariate calibration measurements, multivariate selectivity (SEL(s)) and scalar net analyte signal (scalar NAS), as chromatographic objective functions (COFs), was investigated. Since both assessments are straightforwardly related to the quantification of analytes in the presence of interferents, they were expected to confer new features in the optimisation of compound resolution, not present in conventional assessments. These capabilities are especially interesting in situations of low resolution, where peak deconvolution becomes an attractive alternative. For comparison purposes, chromatographic resolution (R(s)) and peak purity (p(s)) were used as reference COF…
Sample preparation methods for the determination of pesticides in foods using CE-UV/MS.
2010
Much progress has been made in pesticide analysis over the past decade, during this time hyphenated techniques involving highly efficient separation with sensitive detection have become the techniques of choice. Among these, methods based on separation with mass spectrometric detection have resulted in greater likelihood of identification and are acknowledged to be extremely useful and authoritative methods for the determination of pesticide residues but the inherent advantages of the use of CE as a separation technique are well-known and can be summarized as high separation efficiency, low analysis time, high resolution power, and low consumption of samples and reagents. Although UV is the…