Search results for "Absorbance"
showing 10 items of 192 documents
Application of the H-point standard additions method by using absorbance increment values as analytical signals
1991
Abstract This paper demonstrates how the absorbance increment (ΔA) between two wavelengths selected according to the fundamental criteria for application of the H-Point standard additions method (HPSAM) are only related to the analyte concentration. A procedure for calculation of the unknown analyte concentration with no bias error by applying HPSAM to ΔA values in much the same way as the method of standard additions (MOSA), is reported. The method was also applied to a calibration with a single standard. The results obtained on 6 samples with maximal separations between 65 and 0 nm are reported. Finally, the proposed method was applied to the resolution of different phenol-o-cresol mixtur…
Analyte estimation using the generalized H-point standard additions method and a new methodology for locating linear spectral intervals for unknown i…
1998
An improvement in the way to locate linear spectral intervals for unknown interferents which overlap the analyte signal in UV–visible spectrophotometry is offered as an alternative to the method previously described by Campins-Falco et al. (Anal. Chim. Acta, 302, 323 (1995)). In that report, quotients of the second-derivative spectra of the sample and analyte were used. The new method improves on the old one by using first- instead of second-derivative data, thus eliminating the possible divisions by zero (inflection points for the analyte) obtained in the previous procedure. The linear intervals are now obtained by plotting for each wavelength the differences in first-derivative data betwe…
Comparative study of different approaches for the flow injection-fourier transform infrared determination of toluene in gasolines.
1994
Abstract A single channel flow injection manifold has been employed to carry out the direct determination of toluene in gasolines by FT—IR without any sample pretreatment and by using different strategies. Toluene can be directly determined by measuring the absorbance at 728 cm −1 , using a base line established between 835 and 575 cm −1 ; and in this case a limit of detection of 0.01% (v/v) can be obtained with a dynamic range up to 2% (v/v). In some cases it could be convenient to determine toluene by derivative flow-injection FT—IR in order to avoid matrix interferences in the analysis of some types of gasolines. Carrying out the first order derivative FI—FT—IR measurements on the 728 cm…
FIA—FT—IR determination of ibuprofen in pharmaceuticals
1992
A method has been developed for the determination of Ibuprofen (2-[4-isobutylphenyl]-propionic acid) in pharmaceuticals by FT-IR, using the carbonyl band which this compound presents at 1710 cm(-1) in carbon tetrachloride solutions. Samples are dissolved in carbon tetrachloride. In this solvent the excipients are not soluble and so the drug can be directly determined without any additional treatment. The use of a simple FIA manifold permits one to carry out this analysis with a low consumption of reagent and the FT-IR provides a continuous monitoring of the spectral base-line which permits an accurate determination of the maximum in the absorbance band. Also, the FIA system permits easy and…
FT-IR spectroscopy reveals that ash water repellency is highly dependent on ash chemical composition
2013
Abstract After a fire, an ash layer is commonly present, which influences soil properties and hillslope hydrology. The wettability of ash, which can vary from highly absorbent to water repellent, is an important characteristic in this context. Recent work has suggested that ash wettability is related to its degree of combustion, which in turn, can be expected to determine ash chemical composition. In this paper we therefore examine the relationship between ash water repellency and ash chemical composition. Ten ash samples with different wettability were each taken from four burned Mediterranean forest sites located at Albaida (A), Lliber (L), Navalon (N), and Pinoso (P), in the east of Spai…
On the absorbance changes in the photocycle of the photoactive yellow protein: A quantum-chemical analysis
2001
Spectral changes in the photocycle of the photoactive yellow protein (PYP) are investigated by using ab initio multiconfigurational second-order perturbation theory at the available structures experimentally determined. Using the dark ground-state crystal structure [Genick, U. K., Soltis, S. M., Kuhn, P., Canestrelli, I. L. & Getzoff, E. D. (1998) Nature (London) 392, 206–209], the ππ* transition to the lowest excited state is related to the typical blue-light absorption observed at 446 nm. The different nature of the second excited state ( n π*) is consistent with the alternative route detected at 395-nm excitation. The results suggest the low-temperature photoproduct PYP HL as the mo…
Determination of vinegar acidity by attenuated total reflectance infrared measurements through the use of second-order absorbance-pH matrices and par…
2007
Univariate (zero-order), multivariate (first-order) and multiway (second-order) calibrations were assayed for the determination of vinegar acidity using a mechanized procedure based upon vibrational spectroscopy and the emerging multicommutation methodology. The second-order methodology relies on the use of a flow system based on multicommutation and binary sampling. The flow network comprises a set of three-way solenoid valves, computer-controlled to provide facilities to handle the sample and to generate a time-dependent pH gradient using two carrier solutions. The procedure is based on the volumetric fraction variation approach that maintains the same volume of sample solution and dynami…
Flow injection Fourier transform infrared determination of nicotine in tobacco
2000
A fully automated procedure is proposed for the Fourier transform infrared (FTIR) determination of nicotine in tobacco. The method is based on the on-line extraction of nicotine with CHCl3. Samples, weighed inside empty extraction cartridges, were humidified with NH3 and the cartridges were installed in a flow manifold in which they were extracted with 2 ml CHCl3 for 2 min, then 400 microliters of the extract were introduced into a micro-flow cell using a carrier of CHCl3 and the IR spectrum was registered continuously. The absorbance, in the wavenumber range 1334-1300 cm-1, was measured, obtaining a peak as a function of time. The area of this peak was interpolated on a calibration line es…
Development of a polydimethylsiloxane–thymol/nitroprusside composite based sensor involving thymol derivatization for ammonium monitoring in water sa…
2014
This report describes a polydimethylsiloxane (PDMS)-thymol/nitroprusside delivery composite sensor for direct monitoring of ammonium in environmental water samples. The sensor is based on a PDMS support that contains the Berthelot's reaction reagents. To prepare the PDMS-thymol/nitroprusside composite discs, thymol and nitroprusside have been encapsulated in the PDMS matrix, forming a reagent release support which significantly simplifies the analytical measurements, since it avoids the need to prepare derivatizing reagents and sample handling is reduced to the sampling step. When, the PDMS-thymol/nitroprusside composite was introduced in water samples spontaneous release of the chromophore…
Quantification of melanin and hemoglobin in humain skin from multispectral image acquisition: use of a neuronal network combined to a non-negative ma…
2012
International audience; This article presents a multispectral imaging system which, coupled with a neural network-based algorithm, reconstructs reflectance cubes. The reflectance spectra are obtained using artificial neural-netwok reconstruction which generates reflectance cubes from acquired multispectral images. Then, a blind source separation algorithm based on Non-negative Matrix Factorization is used for the decomposition of human skin absorption spectra in its main pigments: melanin and hemoglobin. The analysis is performed on reflectance spectra. The implemented source separation algorithm is based on a multiplicative coefficient upload. The goal is to represent a given spectrum as t…