Search results for "Absorbance"
showing 10 items of 192 documents
Isocratic and gradient elution in micellar liquid chromatography with Brij-35
2015
Polyoxyethylene(23)lauryl ether (known as Brij-35) is a nonionic surfactant, which has been considered as an alternative to the extensively used in micellar liquid chromatography anionic surfactant sodium lauryl (dodecyl) sulfate, for the analysis of drugs and other types of compounds. Brij-35 is the most suitable nonionic surfactant for micellar liquid chromatography, owing to its commercial availability, low cost, low toxicity, high cloud temperature, and low background absorbance. However, it has had minor use. In this work, we gather and discuss some results obtained in our laboratory with several β-blockers, sulfonamides, and flavonoids, concerning the use of Brij-35 as mobile phase mo…
PLS-UV spectrophotometric method for the simultaneous determination of paracetamol, acetylsalicylic acid and caffeine in pharmaceutical formulations
1997
A simple and fast analytical procedure is proposed for the simultaneous determination of paracetamol, acetylsalicylic acid and caffeine in pharmaceuticals by means the partial least square treatment of the spectrophotometric absorbance data between 216 and 300 nm, taken at 5 nm intervals. The method involves the use of 8 standard mixtures of the three compounds assayed, considered at two concentration levels, and the measurement of the absorbance of samples in a 20% (v/v) ethanol in water solution previously filtered. In the analysis of real and synthetic samples precise and accurate values were obtained by the aforementioned procedure, providing in all cases variation coefficients and accu…
Impact of hydroxy and octyloxy substituents of phenothiazine based dyes on the photovoltaic performance
2013
Two novel organic dyes containing hydroxy and octyloxy substituents onto a phenothiazine skeleton were synthesized and their effects on the photovoltaic performance were studied. Hydroxy acts as an ancillary anchoring unit along with the carboxylic group, while the phenothiazine modified moiety acts as an electron donor. The photophysical and electrochemical studies revealed that maximum absorbance of the dye with the hydroxy group in the solution was blue shifted and its band gap increased, indicating that donor acceptor strength was reduced as compared to the octyloxy substituted dye. Furthermore, electron lifetime of the organic dye with the hydroxy moiety was shorter due to smaller resi…
Polypyrrole films functionalized with pendant titanocene dichloride complexes: Ellipsometric study of the electropolymerization process
2007
Electrochemical and ellipsometric methods have been used to study the electropolymerization process of a functionalized monomer, Tc3Py (in which pyrrole is covalently bonded with titanocene dichloride complex) on platinum electrode from a dilute monomer solution in acetonitrile. The deposition has been performed in the potentiodynamic regime. A new method for the acquisition and treatment of ellipsometric data has been proposed which allowed us to analyze the evolution of the film properties at each potential. The model of a single uniform layer was unable to describe the ellipsometric experimental observations with the necessary precision. A proper fitting of the data has been achieved con…
Altered oxidative stress in overtrained athletes
2010
The purpose of the present study was to examine the relationship between oxidative stress and overtraining syndrome. Indicators of oxidative stress (plasma protein carbonyls, nitrotyrosine, and malondialdehyde) and antioxidant status (oxygen radical absorbance capacity) were measured in severely overtrained (two women, five men) and control athletes (five women, five men). Samples were collected from both groups at baseline (i.e. in the overtraining state of overtrained athletes) and after 6 months of recovery, both at rest and immediately after an exercise test to volitional exhaustion. At baseline, overtrained athletes had higher plasma protein carbonyls at rest than controls (mean differ…
Development of Methods for the Evaluation of Olive Oil Oxidation
2012
In this work, the chemical changes produced in an EVOO sample, both in the presence and absence of its phenolic fraction during an accelerated ageing treatment have been studied. The changes produced in phenolic compound concentrations, jointly with the changes observed in free acidity, peroxide value, UV absorbance, fatty acid composition, OSI and T content, were monitored. In addition, transformation of phenolic compounds during the accelerated ageing treatment in EVOO samples with phenolic fraction was also studied.
Secondary brown carbon formation via the dicarbonyl imine pathway: nitrogen heterocycle formation and synergistic effects.
2016
Dicarbonyls are known to be important precursors of so-called atmospheric brown carbon, significantly affecting aerosol optical properties and radiative forcing. In this systematic study we report the formation of light-absorbing nitrogen containing compounds from simple 1,2-, 1,3-, 1,4-, and 1,5-dicarbonyl + amine reactions. A combination of spectrophotometric and mass spectrometric techniques was used to characterize reaction products in solutions mimicking atmospheric particulates. Experiments with individual dicarbonyls and dicarbonyl mixtures in ammonium sulfate and glycine solutions demonstrate that nitrogen heterocycles are common structural motifs of brown carbon chromophores formed…
The generalized H-point standard-additions method to determine analytes present in two different chemical forms in unknown matrix samples. Part II. C…
2000
The generalized H-point standard-additions method (GHPSAM) is used in order to obtain the total Cr(VI) and chromate concentration in water samples whose matrices are completely unknown. Moreover, a new methodology, which is a modification of the GHPSAM, is proposed for the simultaneous determination of the two major chemical forms of Cr(VI) present in the sample. The method is based on the location of spectral intervals where the behaviour of the interferent absorbance can be considered as linear. From these intervals, the analyte concentration free from bias error can be estimated. Spiked samples of dig and harbour water measured in the UV–visible spectral region have been tested to check …
Quantification of minerals from ATR-FTIR spectra with spectral interferences using the MRC method.
2017
A method for quantifying the individual components of mineral samples based on attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) is described, extending the constant ratio (CR) method to analytes absorbing in a common range of wavenumbers. Absorbance values in the spectral region where the analytes absorb relative to the absorbance of an internal standard absorbing at a wavenumber where the analytes do not absorb, permits the quantification of N analytes using measurements at N fixed wavenumbers. The method was tested for mixtures of albite, orthoclase, kaolin and quartz.
Evaluation and elimination of the “blank bias error” using the H-point standard addition method
1992
Abstract The basis of the H-point standard addition method in the cases where the analyte determination requires the use of an absorbent reagent is considered. The method evaluates and eliminates the blank bias error present in such procedures by using the absorbance increment at two selected wavelengths as the analytical signal of the calibration graphs. Three different determinations were tested: the determination of proteins with the biuret method, thorium with thoron and of magnesium with Titan Yellow. These procedures are better described by the proposed method than by the traditional approach using absorbance values against reagent blank.