Search results for "Absorbance"
showing 10 items of 192 documents
Colorimetric determination of alcohols in spirit drinks using a reversible solid sensor
2018
Abstract A sensor for the colorimetric estimation of the alcoholic content has been developed based on the entrapment of the reagent (4-N,N-dioctylamino)-4‘-trifluoroacetylazobenzene (ETHT 4001) into polydimethylsiloxane (PDMS) modified with tretraethylorthosilicate (TEOS). When exposed to an alcoholic media, the sensor delivers ETHT 4001 so that it reacts with alcohols, resulting in a change in the solution color. The diffusion of the entrapped ETHT 4001 from the polymeric sensor to the working solution depends on the hydrophobicity of both the sensor matrix and the media, while the time of exposure determines whether the reagent reacts with methanol, or with methanol and ethanol. Thus, th…
Spectroscopic study of the aluminium/lumogallion system in the presence of non-ionic surfactants
1987
Abstract The effects of different non-ionic ethylene oxide condensate surfactants on the fluorescence and the molecular absorption of the aluminium/lumogallion system are reported. Ethylene oxide condensates with fatty alcohols give higher micellar enhancement factors than tert-octylphenols or nonylphenols; ethylene oxide/propylene oxide copolymers provide only a 50% increase in the fluorescence of the complex. The aluminium/lumogallion seems to form mixed micelles with the fatty alcohol condensates; the strong complex/micelle interaction provides increased absorbance of the complex at 500 nm and higher fluorescence enhancement, allowing the detection of 0.11 μg l −1 aluminium.
Development of Antioxidant Protein Extracts from Gilthead Sea Bream (Sparus aurata) Side Streams Assisted by Pressurized Liquid Extraction (PLE)
2021
The pressurized liquid extraction (PLE) technique was used, for the first time, to obtain protein extracts with antioxidant activity from side streams (muscle, heads, viscera, skin, and tailfins) of gilthead sea bream (Sparus aurata) in order to give added value to these underutilized matrices. Extraction conditions previously optimized for sea bass (Dicentrarchus labrax) side streams were applied. Protein recovery percentages were 22% (muscle), 33% (heads), 78% (viscera), 24% (skin), and 26% (tailfins), which represented an increase of 1.2–4.5-fold compared to control samples (extraction by stirring). The SDS-PAGE profiles revealed that PLE-assisted extraction influenced protein molecular …
Flow-Injection Solid Phase Partial Least-Squares Spectrophotometric Simultaneous Determination of Iron, Nickel and Zinc
2002
A PLS-2 multivariate calibration method has been developed for the simultaneous determination of iron, nickel and zinc in ternary mixtures by solid phase spectrophotometry associated with flow injection analysis. Fe(II), Ni(II) and Zn(II) form color complexes with 1-(2-thiazolylazo)-2-naphthol (TAN), immobilized on a C18 bonded silica support, at pH 6.4. The proposed procedure is based on the different reaction/retention ratios of the studied ions on the solid support. Bilinear spectrophotometric data of the analytes, fixed in the solid support, were recorded in the 400-800 nm wavelength range as a function of time and a partial least squares (PLS-2) algorithm was used to predict results of…
Spectrophotometric determination of promethazine by flow injection analysis and oxidation by CeIV
1992
A flow injection analysis (FIA) procedure is proposed for the determination of promethazine. The sample solution is directly injected into the carrier-reagent stream which comprises a solution of ceric ions in a sulphuric acid medium. The absorbance at 514 nm from the red colour developed by the oxidation of promethazine is measured. Effects of foreign substances have been investigated and the procedure has been applied to the determination of promethazine in a pharmaceutical formulation (tablets).
Fourier transform infrared spectrometric determination of Malathion in pesticide formulations
2004
Abstract An environmentally friendly methodology has been developed for quality control analysis of emulsifiable concentrate pesticide formulations containing Malathion as active ingredient, using flow injection analysis (FIA)–Fourier transform infrared (FTIR) spectrometry. Five microlitres samples were directly injected into a 3 ml closed FIA manifold, in which 2 ml of CHCl 3 was re-circulated at 1.96 ml min −1 . After homogenisation and sample measurement, 2 μl volumes of a Malathion standard were injected, taking absorbance measurements after each injection. Peak height of the chemigrams, established from peak area values between 1027 and 1017 cm −1 , corrected with a baseline fixed from…
Flow injection-FTIR determination of dithiocarbamate pesticides
2000
A flow injection Fourier transform infrared spectrometric procedure has been developed for the determination the dithiocarbamate pesticides Ziram and Thiram in solid samples. All the operations involved, such as extraction, filtration and measurement, were integrated in the experimental set-up in order to avoid excessive manipulation of samples and standards. Ultrasonic assisted and mechanical extraction were evaluated for the solubilization of the analytes and, additionally, the effect of carrier flow rate, sample loop volume and the ratio between sample mass and volume of solvent employed were studied. Quantitative extractions with chloroform were obtained for both Ziram and Thiram, after…
Microorganism adhesion experimental study using silicon dioxide
2018
AbstractIn this study, yeast, Gram positive and Gram negative bacteria were attached to silicon dioxide microparticles or silica in order to measure their absorbance, also known as physical absorption of light, changes using spectrophotometry. The goal of the study was to determine if spectrophotometry is an effective way to distinguish microorganisms and if microorganisms have an affinity for silicon dioxide since it is a suitable material for the production of prostheses. The experiment was done by examining the light absorption properties of yeast, Gram positive and Gram negative bacteria in a spectrophotometer with and without silicon dioxide microparticles. During the experiment there …
Evaluation of the Bioaccessibility of Antioxidant Bioactive Compounds and Minerals of Four Genotypes of Brassicaceae Microgreens
2019
Microgreens constitute an emerging class of fresh, healthy foods due to their nutritional composition. In this study the content of minerals and antioxidant bioactive compounds, and for the first time bioaccessibility, were evaluated in broccoli (Brassica oleracea L. var. italica Plenck), green curly kale (Brassica oleracea var. sabellica L.), red mustard (Brassica juncea (L.) Czern.) and radish (Raphanus sativus L.) hydroponic microgreens. Macro- (K, Ca, Mg) and oligo-elements (Fe, Zn), ascorbic acid, total soluble polyphenols, total carotenoids, total anthocyanins, total isothiocyanates and total antioxidant capacity (Trolox Equivalent Antioxidant Capacity and Oxygen Radical Absorbance Ca…
HPLC-SEC: a new approach to characterise complex wastewater effluents
2016
ABSTRACTThis work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produc…