Search results for "absorption spectroscopy"
showing 10 items of 828 documents
Determination of chromium in foods by flame atomic absorption and inductively coupled plasma spectrometry
1989
The use of direct determination of chromium in human urine by electrothermal atomic absorption spectrometry in diabetic patients.
1991
EDTA excess Zn(II) back-titration in the presence of 4-(2-pyridylazo)-resorcinol indicator and naphthol green beta as inert dye for determining Cr(II…
2006
The colour changes of 4-(2-pyridylazo)-resorcinol and naphthol green beta as new screening metallochromic indicator in back-titration of EDTA excess with Zn(II) to determine Cr(III)/EDTA complex was investigated with the help of tristimulus colorimetry. Specific colour discrimination (SCD) and L*, a*, b* 1976 parameters were successfully applied to evaluate the quality of colour transition at the end-point in non-alkaline media and in the presence of Zn(II) and Ca(II) which resulted in non-interfering species at 1x10(-3) M and 2x10(-3) M, respectively. The above concentrations are comparable with those used for Cr(III). Validation of the fast and accurate reported method was performed by at…
Distribution of Cr and Pb in artificial sea water and their sorption in marine sediments: an example from experimental mesocosms
2016
The uptake of two heavy metals (chromium and lead) in sediments in experimental mesocosms under exposure to different metal concentrations was evaluated by monitoring their concentrations over time both in seawater and in sediment. Two separate experiments under laboratory-controlled conditions were carried out for the two metals. Sediments were collected from a protected natural area characterized by low anthropic influence and were placed in mesocosms that were housed in aquaria each with seawater at a different metal concentration. At pre-established time intervals, seawater and sediment samples were collected from each mesocosm for chemical analyses. Quantification of chromium and lead …
Atomic Absorption Spectrophotometnc Determination of Chromium in Foods
1986
Abstract A method is reported for determination of chromium in foodstuffs. Organic matter is digested with nitric acid, followed by oxidation to Cr(VI) and extraction with methyl isobutyl ketone (MIBK) after HC1 addition. Chromium determinations are performed by flame absorption spectroscopy. Absence of interferences is verified and recovery tests are performed on food samples. Quantitation limit (3.8 ng/mL), accuracy (NBS Standard Reference Material 1573 Tomato Leaves, 4500 ± 500 ng/g, found 3860 ± 409 ng/g), and precision (CV for vegetable matrix = 9.05%, CV for animal matrix = 14.95%) of the procedure are evaluated.
Reduction of ferricytochrome c catalyzed by optically active chromium(III) complexes
2009
The reduction rates of horse heart ferricytochrome c by amalgamated zinc or by electrolysis at fixed potential on a mercury pool as the cathode have been measured in a buffered solution at pH 7.5 by absorption spectrophotometry. In both cases, the reaction was strongly accelerated by the presence of the optically active complexes Lambda-[Cr(III)((S,S)-promp)H(2)O](+) (H(2)promp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(S)-proline]), Delta-[Cr(III)((R,R)-alamp)H(2)O](+) (H(2)alamp = N,N'-[(pyridine-2,6-diyl)bis(methylene)]-bis[(R)-alanine]) and Lambda-[Cr(III)((S,S)-alamp)(H(2)O)(2)](+). These were shown to undergo reversible one-electron reduction to the corresponding labile chromium(…
Determination of chromium in treated crayfish,Procambarus clarkii, by Electrothermal AAS: Study of chromium accumulation in different tissues
1986
In the present study, the authors investigated the accumulation of chromium in muscle, hepatopancreas, antennal glands, and gills of Procambarus clarkii (Girard) from Lake Albufera following Cr(VI)-exposure. Determinations of chromium were made by using Electrothermal Atomic Absorption Spectroscopy and the standard additions method.
Cadmium and lead in infant cereals — electrothermal-atomic absorption spectroscopic determination
1999
Because infant cereals are an important component of the infant diet from the fourth month of life onwards and therefore contribute to the dietetic intake of metals by infants, cadmium and lead were measured in samples of cereals commercially available in Spain. For this purpose an electrothermal atomic absorption (ET-AAS) method for determining cadmium and lead in these products was studied. The ET-AAS instrumental conditions and temperature/time furnace program were selected. The analytical parameters of the method (linearity, detection and quantification limits and precision) show its usefulness in measuring cadmium and lead in infant cereal products. The method was applied to eight diff…
Unveiling Electronic Transitions in Three Novel Chiral Azo-Compounds Using Linear and Nonlinear Circular Dichroism: A Theoretical−Experimental Study
2011
Herein, we report on the experimental and theoretically study of the linear absorption, electronic circular dichroism (ECD) spectra, as well as the two-photon absorption circular-linear dichroism measurements of three different chiral azo derivatives in dimethylsulfoxide solution. Using potential energy surfaces and frontier orbital analysis, we established the most stable conformation for each molecule and elucidated their different electronic transitions. Our theoretical calculations allowed us to unambiguously identify the spectral position of such transitions and correlate them with the spectral profiles observed in the two-photon absorption spectra. To further elucidate the characteris…
Conformational substates of ferricytochrome c revealed by combined optical absorption and electronic circular dichroism spectroscopy at cryogenic tem…
2010
We have investigated the heterogeneity of the Fe(III)–Met80 linkage of horse heart ferricytochrome c by probing the 695 nm charge transfer band with absorption and electronic circular dichroism (ECD) spectroscopy. In order to verify the connection between conformational substates of the Fe(III)–Met80 linkage and the 695 nm band spectral heterogeneity, we have performed experiments as a function of pH (neutral and acidic) and temperature (room and 20 K). At room temperature, the ECD spectrum is blue shifted with respect to the absorption one; the shift is more pronounced at acidic pH and is compatible with the presence of sub-bands. ECD measurements at 20 K highlighted the heterogeneous natu…