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A flow injection catalytic spectrophotometric method is proposed for the determination of nitrite based on its catalytic effect on the redox reaction between naphthol green B and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of naphthol green B at the maximum absorption wavelength of 722 nm. The detection limit...
A chemiluminescence method for the determination of citric acid was developed. The method is based on the enhancement of citric acid on the chemiluminescence light emission of tris-(2,2'-bipyridine)ruthenium(II). In the presence of tris-(2,2'-bipyridine)ruthenium(II), upon the addition of Ce(IV), resulted in intense light emission. The emission intensity is greatly enhanced by the presence of citric...
UV-vis spectrophotometric method for the analysis of cyclohexylamine (CHA) in aqueous medium in the range of 0.3-20 ppm was developed by coupling CHA with sodium 1,2-naphthaquinone-4-sulphonate (NQS). At 470 nm a calibration slope of 0.028 OD ppm -1 was observed. Minimum detection limit was 0.3 ppm with standard deviation of 0.1 ppm. Reagent concentration and solution pH for the analysis...
A synthesized 24-mer single-stranded deoxyribonucleic acid (ssDNA) was covalently immobilized onto a self-assembled aminoethanethiol monolayer modified gold electrode, using water-soluble 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide (EDC). The covalently immobilized ssDNAs were hybridized with complementary ssDNA (cDNA) or yAL 3 gene in solution, forming double-stranded DNAs (dsDNA). Meanwhile,...
An optical sensor for Hg(II) monitoring using a complex of zinc dithizonate immobilised on XAD 7 which is based on reflectance spectrophotometry has been developed in this study. Measurements were made using a kinetic approach whereby the reflectance signal is measured at a fixed time of 5 min. The sensor could be regenerated using a saturated solution of KCl in 1 M sulphuric acid. The sensor was...
A new sensing method (BAW-TAL technique), which combined the bulk acoustic wave (BAW) technique with the gelation reaction of Tachypleus amebocyte lysate (TAL), was used for viscosity and density measurement and applied to the detection of Escherichia coliform (E. coli). This method depended on the fact that the viscosity and density of the mixture increased, and as a result, the resonance frequency...
During the frying process the fat undergoes several chemical and physical changes caused by heat, water and atmospheric oxygen. With prolonged heating time the accumulation of deterioration products leads to organoleptic failures and a decrease of the nutritive value. For the quality control of frying fats or oils the determination of total polar parts by preparative column chromatography is an approved...
A chemiluminescent method using flow injection is described for the determination of cefadroxil monohydrate. The method is based on the chemiluminescence reaction of cefadroxil with potassium permanganate in sulphuric acid, sensitized by quinine. The proposed procedure allows the determination of cefadroxil over the concentration range 0.1-30 μg ml -1 with a detection limit of 0.05 μg...
The effect of several surfactants on the formation of the fluorescent ternary complex oxalate-Alizarin Red S-zirconium(IV) has been studied. In weakly acidic medium and in the presence of cationic surfactants, such as cetylpyridinium chloride, total complex formation is achieved, whereas in aqueous medium or in the presence of non-cationic micelles no significant changes are obtained in comparison...
A rapid and simple on-line method is described for the preconcentration of Mn, Co, Ni, Cu, Zn, Cd and Pb from sea water using 8-hydroxyquinoline immobilized onto silicone tubing (Sil-8-HQ) via the Mannich reaction. Recoveries between 35 and 95% and limits of detection in the ppt range were obtained using a 2 m long Sil-8-HQ tube with a sample flow rate of 1.0 ml min -1 . A tube could...
Diffusion reflectance fourier transform infrared spectroscopy in the mid-IR region was used to assess the authenticity of tea varieties. The differences between the spectra of 12 different tea varieties (seven black, two green, three semifermented grades) were sufficient to allow their discrimination by the soft independent modelling of class analogy classification method or linear discriminant analysis,...
A highly sensitive and simple visual autocatalytic method has been developed for the determination of trace cobalt. The cobalt ion released by the oxidative decomposition of inert bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino-phenolato] cobaltate (Co(III)-5-Br-PAPS) with peroxomonosulfate acts as a catalyst for the oxidative degradation of the complex. Thus a definite time lapse of...
Separation and determination of thorium, uranium and mixed rare-earth elements (RE) as their 2-(2-arsenophenylazo)-1,8-dihydroxyl-7-(4-chloro-2,6-dibromophenylazo)-napht halene-3,6-disulfonic acid (DBC-As) complexes by capillary electrophoresis is presented in this paper. The pre-column derivitization conditions are discussed. Some separation parameters such as pH value, type of carrier electrolyte,...
A method for the simultaneous spectrophotometric determination of the divalent ions of iron, cobalt, nickel and copper based on the formation of their complexes with 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide (DPTH) is proposed. The resolution of quaternary mixtures of these metallic ions was accomplished by several chemometric approaches. A comparative study of the results obtained for simultaneous...
The acid-base and complexation properties of humic acids (HAs) extracted from bohemian brown coals were studied. The acid-base behavior corresponds with the model of HA as a mixture of mono- and diprotic acids. This model was also verified on commercial HA substances (Aldrich and Fluka). HA binds strongly with heavy metal ions and the highest stability constant of HA-metal ion complexes was observed...
Aqueous solutions and blood plasma spiked with selenite (Se(IV)), selenate (Se(VI)), selenomethionine (SeMet) or trimethylselenonium (TMSe) iodide were analyzed by Zeeman-corrected electrothermal atomic absorption spectrometry (ETAAS) using palladium as a chemical modifier, and by inductively coupled plasma mass spectrometry (ICP-MS). Using ETAAS, the sensitivities for Se(IV), SeMet and TMSe in aqueous...
This work describes the use of simultaneous multielement flame atomic absorption spectrometry for the determination of cadmium, lead, and nickel in burned and unburned Venezuelan crude oil (5 ml volumes) in controlled laboratory experiments. The simultaneous detection limits were 0.010 μg ml -1 (Cd), 0.04 μg ml -1 (Pb), and 0.40 μg ml -1 (Ni) with precision's...
Ferric 2-hydroxy-1-naphthaldehyde thiosemicarbazone (Fe III -HNT) has been synthesized and used to mimic the active group of horseradish peroxidase (HRP). The catalytic characteristics of this mimic-enzyme catalyst in the oxidation reaction of ascorbic acid with hydrogen peroxide has been studied. The experimental results showed that this peroxidase model compound has similar catalytic...
Ribonucleic acid (RNA) is used as a novel ionophore in plasticized poly(vinyl chloride) matrix membrane sensors for some transition metal ions. Membranes incorporating RNA and doped in Cu 2+ , Cd 2+ and Fe 2+ display fast near-Nernstian and stable responses for these ions with cationic slopes of 31.1, 31.3 and 35.5 mV per decade, respectively, over the concentration...
A microfabricated, flat form, amperometric microcell (microchip) is used in a simple, two-electrode arrangement for putrescine oxidase enzyme activity determinations. The cell contains a platinum microdisk working electrode and an Ag/AgCl reference electrode covered by a porous, hydrophilic membrane. An electrochemically-prepared size-exclusion layer is applied on the working electrode surface, to...
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