Search results for "Derivative"
showing 10 items of 1074 documents
Approaches to characterise chromatographic column performance based on global parameters accounting for peak broadening and skewness.
2009
Peak broadening and skewness are fundamental parameters in chromatography, since they affect the resolution capability of a chromatographic column. A common practice to characterise chromatographic columns is to estimate the efficiency and asymmetry factor for the peaks of one or more solutes eluted at selected experimental conditions. This has the drawback that the extra-column contributions to the peak variance and skewness make the peak shape parameters depend on the retention time. We propose and discuss here the use of several approaches that allow the estimation of global parameters (non-dependent on the retention time) to describe the column performance. The global parameters arise f…
Development of the H-point standard additions method for coupled liquid chromatography and UV-visible spectrophotometry
1992
Abstract This work establishes the fundamentals of the H-point standard additions method for liquid chromatography for the simultaneous analysis of binary mixtures with overlapped chromatographic peaks. The method was compared with the deconvolution method of peak suppression and the second derivative of elution profiles. Different mixtures of diuretics were satisfactorily resolved.
Fast enantiomeric separation of uniconazole and diniconazole by electrokinetic chromatography using an anionic cyclodextrin: application to the deter…
2000
The enantiomeric resolution of the fungicides uniconazole and diniconazole was performed using electrokinetic chromatography with cyclodextrins as pseudostationary phase (CD-EKC). A systematic evaluation of several chiral selectors was made. The anionic derivative carboxymethylated-gamma-cyclodextrin (CM-gamma-CD) was found to be the most appropriate for the enantioseparation of fungicides among all cyclodextrins tested. The influence of some experimental conditions such as nature and buffer pH, chiral selector concentration, and temperature on the enantiomeric separation of the compounds studied was also investigated. The use of a 50 mM phosphate buffer (pH 6.5) containing 5 mM CM-gamma-CD…
Solving Rate of Change Tasks with a Graphing Calculator: a Case Study on Instrumental Genesis
2016
In an increasing number of mathematics classes throughout the world, technology is being used for the teaching and learning of mathematics. But knowledge is limited about the long-term development of students’ mathematical thinking when learning mathematics with the use of technology. This article reports on the development of a student and the role of the graphing calculator (GC) in his learning about derivatives and instantaneous rate of change. This case is compelling, because the student is an intensive user of the GC and develops flexible problem-solving techniques – techniques which differ from those of his peers and from what he was taught in mathematics class. We used the framework …
Multi-technique approach for qualitative and quantitative characterization of furazidin degradation kinetics under alkaline conditions
2016
Degradation of drug furazidin was studied under different conditions of environmental pH (11-13) and temperature (30-60°C). The novel approach of hybrid hard- and soft-multivariate curve resolution-alternating least squares (HS-MCR-ALS) method was applied to UV-vis spectral data to determine a valid kinetic model and kinetic parameters of the degradation process. The system was found to be comprised of three main species and best characterized by two consecutive first-order reactions. Furazidin degradation rate was found to be highly dependent on the applied environmental conditions, showing more prominent differences between both degradation steps towards higher pH and temperature. Complim…
Comparison of several methods used for the determination of cephalosporins. Analysis of cephalexin in pharmaceutical samples
2002
The precision of UV absorbance of intact and acid degraded cephalosporins, ninhydrin, high performance liquid chromatography and iodometric methods used for analysis of cefoxitin, cefotaxime, cephazolin and cephalexin were compared. To obtain the calibration graphs the analytical signal used were: absorbance, first derivative absorbance, second derivative absorbance and H-point Standard Additions Method by using absorbance values at two selected wavelengths as analytical signal. These methods and calibration graphs were also used for the determination of cephalexin in pharmaceutical samples.
SAR-studies of γ-secretase modulators with PPARγ-agonistic and 5-lipoxygenase-inhibitory activity for Alzheimer’s disease
2014
Abstract We present the design, synthesis and biological evaluation of compounds containing a 2-(benzylidene)hexanoic acid scaffold as multi-target directed γ-secretase-modulators. Broad structural variations were undertaken to elucidate the structure–activity-relationships at the 5-position of the aromatic core. Compound 13 showed the most potent activity profile with IC50 values of 0.79 μM (Aβ42), 0.3 μM (5-lipoxygenase) and an EC50 value of 4.64 μM for PPARγ-activation. This derivative is the first compound exhibiting low micromolar to nanomolar activities for these three targets. Combining γ-secretase-modulation, PPARγ-agonism and inhibition of 5-lipoxygenase in one compound could be a …
Differential properties of the Moreau envelope
2014
International audience; In a vector space endowed with a uniformly Gâteaux differentiable norm, it is proved that the Moreau envelope enjoys many remarkable differential properties and that its subdifferential can be completely described through a certain approximate proximal mapping. This description shows in particular that the Moreau envelope is essentially directionally smooth. New differential properties are derived for the distance function associated with a closed set. Moreover, the analysis, when applied to the investigation of the convexity of Tchebyshev sets, allows us to recover several known results in the literature and to provide some new ones.
Metabolism of polychlorinated norbornenes by Clostridium butyricum.
1972
STUDIES of the metabolism of cyclodien-insecticides, such as dieldrin, endrin, endosulphan, have revealed valuable information about their fate in the ecosystem1. With all metabolites identified so far, however, the hexachlorinated norbornene moiety remains unchanged2,3. Only from photodieldrin, a cage-like derivative of dieldrin, have dechlorinated metabolites been reported4,5.