Search results for "Spectroscopy"
showing 10 items of 10293 documents
Automated trace enrichment for screening and/or determination of primary, secondary and tertiary amphetamines in biological samples by liquid chromat…
1999
A rapid and simple liquid chromatographic method for the automated determination of amphetamines in biological fluids was developed. The proposed procedure is based on the injection of 250 microL of sample into a 20 x 2.1 mm id precolumn (packed with a 30 microns Hypersil C18 stationary phase) for enrichment and purification of the analytes. Next, the analytes are transferred to a 5 microns LiChrospher 100 RP18, 125 x 4 mm id analytical column for their separation under reversed-phase conditions. Water was used to eliminate the matrix components from the precolumn and a 0.2 M phosphate buffer (pH 3) containing 2% triethylamine was the mobile phase for the resolution of the amphetamines. The…
Simultaneous homogeneous immunoassay of phenytoin and phenobarbital using a Nafion-loaded carbon paste electrode and two redox cationic labels
1997
Abstract The dual-analyte homogeneous immunoassay of two antiepileptic drugs was carried out simultaneously at physiological pH by square-wave voltammetry at a Nafion-loaded carbon paste electrode. Phenobarbital (PB) and phenytoin (DPH) were labeled by a cobaltocenium salt (Cc+) and a ferroceneammonium salt (N+Fc), respectively, and the corresponding standard redox potentials were −1.05 V and 0.26 V. Detection limits of 0.25 and 0.2 μM were achieved for PB-Cc+ and DPH-N+Fc (S/N = 3) after a 5-minute accumulation step, with linear responses over the 0.25–5 and 0.2–5 μM ranges, respectively. The relative standard deviation was evaluated to be ≥ 11% for 1 μM of each labeled drug. The separate,…
Thermal Lens Spectrometric Detection of Catecholamines after Oxidation to Aminochromes
1992
Abstract Experimental conditions for the spectrophotometric and thermal lens spectrometry (TLS) detection of catecholamines after oxidation to aminochromes with hexacyanoferrate (III) are optimized. At the low concentrations used in TLS, and in a 0.07 M citrate buffer, catecholamine oxidation can be performed at pH 7 and is immediate, whereas a lower pH value is required in spectrophotometry to avoid aminochrome polymerisation, the oxidation reactions being much slower. Similar TLS sensitivities are obtained for all catecholamines which facilitates HPLC evaluation. Sensitivity can be enhanced using a 50% ethanol-water medium. The linear dynamic range extends over two orders of magnitude, th…
Electrochemical detection of chloride ions using Ag-based electrodes obtained from compact disc
2022
Abstract In this work electrochemical sensors fabricated from compact disc material (waste or new) are used to quantify chloride ions in different types of samples. All three electrodes, working, counter, and pseudo-reference electrodes, were fabricated from the compact disc and directly used. Different parameters were studied in order to demonstrate the possibility of using this waste material for efficient and low-cost electrochemical sensors. Chloride sensing performance was evaluated using linear scan voltammetry as the detection technique. A sensitivity of 0.174 mA mM−1 cm−2 with a limit of detection of 20 μM and excellent selectivity against many interferents was observed. Selectivity…
Selective chlorine determination by gas diffusion in a tandem flow assembly and spectrophotometric detection with o-dianisidine
2001
Abstract A fast, selective, sensitive and automated method for determination of free chlorine in industrial formulations and water samples is proposed. The automation of the flow assembly is based on the “tandem flow” approach, which uses a set of solenoid valves acting as independent switches. The operating cycle for obtaining a typical analytical transient signal can easily be programmed by means of friendly software running in the Windows environment. The manifold is provided with a gas diffusion unit which permits the removal of interfering species as well as concentrating the chlorine. The determination of chlorine is performed on the basis of the oxidation of o-dianisidine as the colo…
Capillary zone electrophoresis for the determination of thiabendazole, prochloraz and procymidone in grapes
2001
Capillary zone electrophoresis with UV detection was applied to the simultaneous determination of thiabendazole, prochloraz and procymidone in grapes. Electrolyte conditions such as pH, composition and concentration of the buffer, addition of organic solvent and working voltage were checked to obtain a high-performance separation of the three fungicides (by measurement of separation efficiency and resolution). The most critical parameter was the pH of the running buffer. The best separation was achieved in 4 mM phosphate solution at pH 3.5. The repeatability of the migration times, expressed as RSD, was <0.44%. The three peaks were completely resolved with a separation efficiency up to 100 …
Optimization of transmission near infrared spectrometry procedures for quality control of pesticide formulations
2006
The use of different response functions to be optimized in the frame of the use of near infrared spectrometry for quality control of active principles in agrochemical formulations has been evaluated. Both, simple functions, based on parameters like sensitivity, repeatability, accuracy, signal to noise ratio, limit of detection or sample throughput, and a complex function, considering all the aforementioned aspects, were employed in the development of a new method for Iprodione determination in agrochemicals. Optimization strategies were based on the previous screening of the most important instrumental factors like number of cumulated scans, nominal resolution, mirror velocity and zero fill…
Environmentally friendly analytical chemistry through automation: comparative study of strategies for carbaryl determination with p-aminophenol
1999
Abstract A flow system, based on multicommutation and binary sampling, has been developed for improving the automated spectrophotometric determination of carbaryl with p -aminophenol (PAP) in order to reduce the waste volume and to preserve the maximum analytical performance. The procedure, which was implemented employing a flow network obtained by nesting five, three-way solenoid valves controlled by means of a 386 microcomputer equipped with an electronic interface running software written in quick basic 4.5, provides a limit of detection of 26 μg l −1 , comparable to that obtained using a conventional flow injection (FIA) manifold and lower than that found by sequential injection analysi…
Indirect spectrophotometric determination of p-aminobenzoic acid in sunscreen formulations by sequential injection analysis
2003
Abstract A simple indirect sequential injection spectrophotometric method for the determination of the UV-filter p -aminobenzoic acid (PABA) in sunscreen formulations is proposed. The determination is based on the reaction of PABA with hypochlorite in acidic medium and the subsequent measurement of the residual chlorine by using the well-known reaction with o -tolidine. The experimental variables involved in the sequential injection analysis (SIA) system (sandwich arrangement, volumes of sample and reagents, propulsion flow rate, reaction coil length) and adequate concentrations of reagents were studied. The SIA method has a linear range up to 20 μg ml −1 (3 s y / x / b detection limit) of …
Indirect Determination of Cyanide by Atomic Absorption Spectrometry
1995
Abstract Two methods for determination of cyanide by atomic absorption spectrometry (AAS) are developed. Both methods are based on the formation of an ion association compound between a metal complex, (Ag(CN)2 − or Cu(CN)3 2-), and a quaternary ammonium ion (benzyldimethylhexadecylammonium ion). The ion association compound is extracted into isomethylbutylketone (IBMK) and the metal is determined by AAS directly in extract. The method based on the formation of silver cyanide complex provides a reproducibility of 2.5%, a recovery of 99% and a detection limit of 1.7 μg/L while the method based on the formation of copper complex gives a reproducibility of 6%, a recovery of 93% and a detection …