Search results for "Deriva"
showing 10 items of 1423 documents
Limits of multi-linear gradient optimisation in reversed-phase liquid chromatography
2005
Abstract The concept of limiting peak purity was applied to quantify the degree of completion of the separation capability of a chromatographic system using multi-linear gradients. The objective was to check whether the complexity of a gradient program deserves be increased to enhance resolution by inserting more linear segments, or on the contrary, no significant improvements can be expected under more complex gradients. A set of 19 isoindole derivatives of primary amino acids was selected to test the performance of isocratic, single linear and multi-linear gradients. Accurate simulated chromatograms were obtained via numerical integration of the general equation of gradient elution, using…
Study of Burseraceae resins used in binding media and varnishes from artworks by gas chromatography–mass spectrometry and pyrolysis-gas chromatograph…
2005
In the present work, a study attempting to characterize the Manila elemi and Mexican copal resins from the Burseraceae family, which are used as components of varnishes and binding media of artworks, has been carried out. A new GC-MS method involving the use of methyl chloroformate as derivatisation reagent has been proposed. A second method which uses pyrolysis-GC-MS and hexamethyldisilazane as derivatization reagent has also been applied. Characterization of the main components of the mono-, sesqui- and triterpenoid fractions occurring in the raw materials has been achieved. Both alpha- and beta-amyrin have been established as the major triterpenoid compounds occurring in these resins tog…
Kinetic-Spectrophotometric Determination of Primary and Secondary Amines by Reaction with 1-2 Naphthoquinone-4-Sulphonate.
1994
Abstract A kinetic-spectrophotometric method for the determination of primary and secondary amines is described. It is based on the coloured reaction of these amines with sodium 1,2 Naphthoquinone 4-sulphonate (NQS) in the presence of a non-ionic surfactant. For each determination the optimum conditions were studied and found to be as follows: pH 10.5. Carbonate-bicarbonate buffer 0.1M, Triton X-100 0.1%, Temperature 45°C, and NQS 6.4 × 10−3 M and interval of time 45–180s at wavelength 490 nm. The parameters used for the quantitative determinations are the reaction rate and the increase in the absorbance of the kinetic curves. This procedure has been applied to the determination of ephedrin…
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.
Simultaneous Kinetic Determination of Carbamate Pesticides after Derivatization withp-Aminophenol by Using Partial Least Squares
1996
Abstract A method has been developed for the fast spectrophotometric determination of propoxur, carbaryl, and ethiofencarb in water samples using injection analysis in the stopped-flow mode. The method is based on the reaction between p -aminophenol and the phenolic compounds obtained from the pesticides, after a previous hydrolysis with 0.05 M NaOH at room temperature for 15 min. The partial least-squares treatment of the spectrophotometry kinetic data provides a simultaneous determination of the three carbamate pesticides assayed with a relative accuracy error lower than 5% in complex mixtures also containing formetanate, which is only partially hydrolyzed under the experimental condition…
Rapid and simultaneous high-performance liquid chromatography assay of polyamines and monoacetylpolyamines in biological specimens
2000
A rapid, resolutive and reproducible reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed for polyamines and acetylpolyamines by adopting pre-column derivatization with benzoyl chloride. In a single run lasting less than 15 min ten polyamines were separated as well as traces of benzoic acid, methylbenzoate and benzoic anhydride. These contaminants, produced during the derivatization reaction, were almost all eliminated by washing steps envisaged in the same procedure. This simple and sensitive method can be applied to routine determination of polyamines in biological samples. A fine application of this procedure to the determination of endogenous content of p…
Separation of the enantiomers of primary and secondary amphetamines by liquid chromatography after derivatization with (−)-1-(9-fluorenyl)ethyl chlor…
2003
The chiral reagent (−)-1-(9-fluorenyl)ethyl chloroformate (FLEC) has been evaluated for the enantioselective analysis of amphetamines by liquid chromatography. For separation of the FLEC diastereomers conventional reversed-phase conditions were used. The conditions affording the best enantiomeric resolution and sensitivity were determined for amphetamine, methamphetamine, ephedrine, pseudoephedrine, 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA), and 3,4-methylenedioxyethylamphetamine (MDE). All the amphetamines assayed could be separated with resolution factors ranging from 0.91 to 1.92. Although FLEC is typically used as a fluorogenic reagent, it was shown t…
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…
Cisplatin derivative loaded in mesoporous MCM-41: preparation and characterization
2014
The aim of this study is to design and investigate a new material constituted by mesoporous silica MCM-41 and a new cisplatin derivative, cis-PtCl2(DMSO)HL]•2DMSO, where HL = 7-amino-2-(methylthio)[1,2,4]triazolo[1,5-a]pyrimidine-6-carboxylic acid, having biological activity.[1] The high surface area and the tunable pore size of MCM-41 allow it for loading vast amounts of bioactive molecules, including biocides and drugs. Mesoporous silica MCM-41 was prepared in alkaline environment from tetraethoxysilane as Si source and cetyltrimethylammonium bromide (CTAB) as template. [2] Amino groups have been successfully grafted onto the pore surface with 3-aminopropyl triethoxysilane (APTES) in orde…
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 …