Search results for "Spectroscopy"
showing 10 items of 10293 documents
Flow injection determination of free and total cholesterol in animal greases using enzymes in non-aqueous media
1998
A non-covalently coimmobilized bienzymic reactor of horseradish peroxidase (HRP) and cholesterol oxidase (COD), operating in a continuous organic flowing stream of 1 × 10–3 M p-anisidine in buffer-saturated (pH 7.0) toluene, has been employed for cholesterol determination in animal greases, such as pig, beef, and chicken fat, and codfish liver oil. The method provides a good linear relationship up to 1.8 × 10–3 M cholesterol and average recoveries of 99.5%, a high sensitivity, with a detection limit of 1 × 10–6 M of cholesterol and a good precision (an interday RSD of 1.8% for the determination of total cholesterol in a codfish oil sample). The method permits the direct spectrophotometric d…
o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine
2002
A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent…
Zwitterionic Sulfonates as m/z Shift Reagents for 5-Methylcytosine Detection in Deoxyribonucleic Acids (DNA) Using Flow Injection Analysis and Electr…
2015
5-Methylcytosine (5-MC) is an important epigenetic modification of DNA. Abnormally high concentrations of this substance appear because of the hypermethylation of cytosine. Therefore, the measurement of the quantity of this compound in mammals is of great importance. Recently, we reported that several imidazolium-based zwitterionic sulfonates form complexes with 5-MC in solution, which can be studied by electrospray ionisation mass spectrometry (ESI-MS). It is shown in this paper that such an association can be utilised for the detection of 5-MC in a DNA sample using high-throughput a flow injection analysis ESI-MS method. A variety of the sulfonate zwitterions have been tested as m/ z shi…
Flow injection biamperometric determination of chloramphenicol and related nitro compounds by on-line chemical photodegradation
2000
Abstract An unsegmented continuous-flow assembly for the determination of chloramphenicol is proposed. The determination is based on the on-line photodegradation of the drug in an NH4+/NH3 buffer at pH 10.4 by using a photoreactor consisting of a 697 cm long × 0.8 mm ID piece of PTFE tubing coiled around an 8 W low-pressure mercury lamp. Photodegraded chloramphenicol is detected by photolytic cleavage of nitrite from the parent compound as well as by organic oxidizing photofragments, and their subsequent reaction with iodide ion, which is monitored biamperometrically. Triiodide thus formed is detected in excess iodide solution by polarizing two platinum electrodes at 100 mV. The calibration…
Improvement of the electrophoretic protein profiles of Leguminosae gums extracts using gamanase and application to the evaluation of carob–guar mixtu…
2004
Abstract A quantitative assay for guar gum in carob gum, based on the extraction of proteins in acetonitrile–water (7:3), separation by capillary electrophoresis and multiple linear regression (MLR) using the areas of nine selected peaks as predictors, was improved by performing the extraction in the presence of gamanase. In the absence of the enzyme, peak migration times and areas depended on the guar content, which complicated peak identification and evaluation. Manual correction of the migration times by comparison with standard electropherograms obtained with pure carob and carob–guar mixtures was required; however, when the proteins were extracted under sonication at 60 °C for 30 min i…
High-frequency electrodeless discharge lamps for atomic absorption analysis
2003
Abstract In this paper we present the results of an investigation of high-frequency electrodeless discharge lamps (HFEDLs), containing Cd, Zn, Hg, As, Te, Se, Pb, Sn, Tl and Bi, developed in our laboratories as light sources for atomic absorption spectrometry (AAS). Important physical processes in the lamps are discussed. Essential characteristics of HFEDLs for AAS, such as intensity, stability and operating life are considered. The intensities and detection limits are compared with the corresponding characteristics of hollow cathode lamps. The temporal behavior of an As HFEDL is compared with that of a commercially available electrodeless discharge lamp. Detection limits in graphite furnac…
Simultaneous determination of hydride and non-hydride forming elements by inductively coupled plasma optical emission spectrometry
2011
e percentagens de recuperacao entre 97 e 103%. A aplicabilidade do sistema foi demonstrada na determinacao simultânea de Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Zn, As, Bi, Sb, Se e Te em amostras certificadas para elementos tracos, NIST 1549 (leite em po desnatado), NIST 1570a (folhas de espinafre), DORM-2 (musculo de cacao) e TORT-2 (hepatopâncreas de lagosta). Os resultados obtidos foram concordantes com os teores certificados. The operating characteristics of a dual nebulization system were studied including instrumental and chemical conditions for the hydride generation and analytical figures of merit for both, hydride and non hydride forming elements. Analytical performance of the neb…
Development of a non-chromatographic method for the speciation analysis of inorganic antimony in mushroom samples by hydride generation atomic fluore…
2009
Abstract A simple and sensitive method has been developed for the direct determination of toxic species of antimony in mushroom samples by hydride generation atomic fluorescence spectrometry (HG AFS). The determination of Sb(III) and Sb(V) was based on the efficiency of hydride generation employing NaBH 4 , with and without a previous KI reduction, using proportional equations corresponding to the two different measurement conditions. The extraction efficiency of total antimony and the stability of Sb(III) and Sb(V) in different extraction media (nitric, sulfuric, hydrochloric, acetic acid, methanol and ethanol) were evaluated. Results demonstrated that, based on the extraction yield and th…
Speciation of selenium and tellurium in milk by hydride generation atomic fluorescence spectrometry
2004
A simple, fast and highly sensitive method has been developed for the differentiation of Se and Te into their (IV) and (VI) oxidation states in milk samples by HG-AFS. This procedure involves a previous leaching of milk slurries by sonication with aqua regia for 10 min. Se(IV) and Te(IV) were determined by analysis of the samples without a pre-reduction step; being total Se and Te determined after reduction with KBr. The method provides limit of detection values (LOD) of 0.012 and 0.023 ng ml−1 for Se(IV) and Te(IV) respectively. Average relative standard deviation values of 10.5%, 3.9%, 12% and 12.5% were found for the determination of Se(IV), Se(VI), Te(IV) and Te(VI) in milk samples cont…
Non-chromatographic speciation analysis of arsenic and antimony in milk hydride generation atomic fluorescence spectrometry
2003
Abstract A rapid, high sensitivity method has been developed for the determination of As(III), As(V), Sb(III) and Sb(V) in milk samples by using hydride generation atomic fluorescence spectrometry. The method is based on the leaching of As and Sb from milk through the sonication of samples with aqua regia followed by direct determination of the corresponding hydrides both before and after reduction with KI. It was confirmed by recovery experiments on spiked commercially available samples that neither the reduced nor the oxidized forms of the elements under study or mixtures of the two oxidation states were modified by the room temperature sample treatment with aqua regia. The methodologies …