Search results for "Absorbance"
showing 10 items of 192 documents
Quality control of pharmaceuticals containing clenbuterol by thermal lens spectrometry.
1996
An ultrasensitive absorptiometric procedure for the determination of clenbuterol in pharmaceutical preparations was developed. Clenbuterol was diazotized with nitrite and coupled with 1-(naphthyl)ethylenediamine, and the absorbance of the azo dye formed was measured by both spectrophotometry and ultrasensitive thermal lens spectrometry (TLS). The TLS limit of detection was 1.5 ppb, 14-fold lower than with a Hewlett-Packard diode array spectrophotometer. Thus, the TLS procedure can be advantageously applied to quality control of clenbuterol at the individual dose level and in small samples. Repeatability as relative standard deviation was 1.5% (50 ppb, n = 6).
Spectrophotometric determination of mercury(II) and silver(I) with copper(II) and diethyldithiocarbamate in the presence of triton X-100
1986
Abstract Procedures for the determination of mercury and silver by displacement of diethyldithiocarbamate (DDTC) from its copper complex in the presence of 1% Triton X-100, and measurement of the decrease in the Cu(DDTC) 2 absorbance, are described. The use of the surfactant avoids the need for an extraction step. Reproducibility within 1% and detection limits of 0.25 ppm Hg(II) and 0.45 ppm Ag(I) have been obtained, and linear calibration ranges up to 13 ppm Hg(II) and 15 ppm Ag(I). In the presence of 0.1 M EDTA very good selectivity is achieved.
Micropumping multicommutation turbidimetric analysis of waters
2007
Abstract A micropumping multicommutation manifold to perform turbidity determinations in waters is described. The procedure is based on the use of a combination of hydrazine sulfate and hexamethylenetetramine, to obtain an external standard of nephelometric turbidity units (NTU), which could compare the absorbance measurements at high wavelengths for samples with a calibration line obtained from a concentrated formazine standard diluted on-line. To minimize sample and reagent consumption and waste generation, the flow system was designed with two solenoid micro-pumps, one of them for the alternative introduction of the formazine standard and samples and the other one for the water carrier. …
Direct ATR-FTIR determination of sucrose in beet root.
2000
A simple and fast procedure has been developed for the direct determination of sucrose in beet root samples through attenuated total reflectance Fourier transform infrared absorbance measurements (ATR-FTIR) at 1056 cm(-1) with a baseline established between 1187 and 887 cm(-1). The method only requires a previous crushing or liquefaction of samples and it is free from matrix effects and from the interference of minoritary sugars and fermentation molecules. Aqueous solutions of sucrose can be used as standards and recovery values from 101 to 103% were found for spiked concentration levels from 3.5 to 10.5% (w/w). The limit of detection provided by this method corresponds to 0.15% (w/w) of su…
Fourier transform infrared spectrometric determination of Ziram.
2001
A procedure has been developed for vapour-phase Fourier transform infrared determination of Ziram, a dithiocarbamate pesticide. The method is based on the evolution of CS(2), after decomposition of the dithiocarbamate with diluted H(2)SO(4) at 50 degrees C. The CS(2) evolved was swept by a carrier flow of nitrogen to a laboratory-made infrared gas cell of 39 mm pathlength and 490 mul volume. The signals were registered as a function of time. The area of peaks obtained from absorbance measurement in the wavenumber range between 1600 and 1450 cm(-1) were interpolated in a calibration line established from Ziram standards treated in the same way as samples. The method provided an absolute limi…
Resolution of overlapped non-absorbing and absorbing solutes using either an absorption null-balance detection window or multivariate deconvolution a…
2004
Abstract Non-absorbing alkyl ether sulfates (AES) can be separated using anthraquinone-2-carboxylic acid (AQCA) as a probe; however, absorbing alkyl benzene sulfonates (ABS), if present, interfere indirect detection of most AES oligomers. Overcoming of this interference, as well as the simultaneous characterisation and evaluation of AES, fatty acids and ABS, was accomplished by using a diode-array detector and the procedures here discussed. First, it was shown that ABS can be made undetectable by using a 9 nm wide and 227 nm centred charge-absorptivity null-balance detection window (NBDW), where its contribution to the absorbance cancels the dilution effects that its presence induces on the…
A Colorimetric Membrane-Based Sensor with Improved Selectivity towards Amphetamine
2021
Due to their simplicity, speed and low cost, chemical spot tests are increasingly demanded for the presumptive identification of illicit drugs in a variety of contexts such as point-of-care assistance or prosecution of drug trafficking. However, most of the colorimetric reactions used in these tests are, at best, drug class selective. Therefore, the development of tests based on chemical reactions with improved discrimination power is of great interest. In this work, we propose a new colorimetric assay for amphetamine (AMP) based on its reaction with solutions of alkaline gold bromide to form an insoluble yellow–orange derivative. The resulting suspensions are then filtered onto nylon membr…
Metal oxide semiconductor sensors for monitoring of oxidative status evolution and sensory analysis of virgin olive oils with different phenolic cont…
2009
An electronic nose based on an array of six metal oxide semiconductor sensors was used to monitor the oxidative status of virgin olive oils (VOO) during storage. VOO samples, with and without phenolic compounds, were stored at 60 °C for 7 weeks. Once a week, absorbance at 232 and 270 nm, oxidized stability index, electronic nose, and sensory analysis were evaluated. Linear discriminant analysis models were constructed in order to classify samples according to oxidative levels. Based on these models, VOO samples with and without phenolic compounds at different storage times, divided in eight categories, were correctly classified also achieving a good correlation for sensory analysis. The met…
The impact of soil erosion on soil fertility and vine vigor. A multidisciplinary approach based on field, laboratory and remote sensing approaches
2018
Soil erosion processes in vineyards, beyond surface runoff and sediment transport, have a strong effect on soil organic carbon (SOC) loss and redistribution along the slope. Variation in SOC across the landscape can determine differences in soil fertility and vine vigor. The goal of this research was to analyze the interactions among vines vigor, sediment delivery and SOC in a sloping vineyard located in Sicily. Six pedons were studied along the slope by digging 6 pits up to 60 cm depth. Soil was sampled every 10 cm and SOC, water extractable organic carbon (WEOC) and specific ultraviolet absorbance (SUVA) were analyzed. Erosion rates, detachment and deposition areas were measured by the po…
EXTREMELY LOW FREQUENCY (50Hz) MAGNETIC FIELD INFLUENCES PHYSICO-CHEMICAL PROPERTIES OF WATER
2019
The influence of 50 Hz sinusoidal magnetic field on physico-chemical properties of water was studied. Tanks with distilled water (120 mL) were individually exposed to action of homogenous 50 Hz magnetic fields, using a Helmholtz coils system. For magnetically exposure have been used different values of magnetic flux density (between 1 and 5 mT) and different durations of exposure (between 5 and 240 minutes). By means of this experimental study the physico-chemical properties of exposed water samples compared with the control ones have explored. Density, viscosity, surface tension, pH, oxygen concentration and electrical conductivity were recorded. Some physico-chemical parameters analyzed i…