Search results for "Spectrophotometry"
showing 10 items of 644 documents
Non-chromatographic speciation of toxic arsenic in vegetables by hydride generation-atomic fluorescence spectrometry after ultrasound-assisted extrac…
2007
A non-chromatographic, sensitive and simple analytical method has been developed for the determination of toxic arsenic species in vegetable samples by hydride generation-atomic fluorescence spectrometry (HG-AFS). As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were determined by hydride generation-atomic fluorescence spectrometry using a series of proportional equations. The method is based on a single extraction of the arsenic species considered from vegetables through sonication at room temperature with H(3)PO(4) 1 mol L(-1) in the presence of 0.1% (w/v) Triton XT-114 and washing of the solid phase with 0.1% (w/v) EDTA, followed by direct measurement of the co…
Use of micellar mobile phases for the chromatographic determination of clorazepate, diazepam, and diltiazem in pharmaceuticals
2001
An ODS-2 column, a micellar mobile phase of high elution strength containing 0.1M sodium dodecyl sulfate and 3% (v/v) butanol, and ultraviolet detection at 230 nm are used for the determination of either of two benzodiazepines (clorazepate and diazepam) and a benzothiazepine (diltiazem) in pharmaceuticals. The procedure is shown to be competitive against conventional chromatography with methanol-water mobile phases, especially for diltiazem. The composition of the micellar mobile phase is selected using a predictive strategy based on an accurate retention model and assisted by computer simulation. Calibration graphs are linear at least in the 2.5 to 20 microg/mL, 4 to 20 microg/mL, and 5 to…
Implementing the contamination prevention programs in the pesticide industry by infrared spectroscopy.
2014
Abstract An infrared spectroscopy based methodology has been successfully developed to implement contamination prevention programs in the pesticide industry. Sensitivity of the IR procedure, traditionally considered the Achilles Hell of the technique, has been improved by using a transmission cell with an open upper side, an internal volume of 35 µL and an optical pathlength of 0.5 mm, providing detection limits of 32 mg L−1 for folpet and 48 mg L−1 for cymoxanil. The manufacturing of folpet and cymoxanil was employed as an example and the IR methodology was validated for the implementation of contamination prevention programs in the pesticide industry. The swab test and rinsate method were…
Amphetamine and methamphetamine determination in urine by reversed-phase high-performance liquid chromatography with sodium 1,2-napthoquinone 4-sulfo…
1995
A rapid method is described for the identification and determination of amphetamine and methamphetamine in human urine samples by liquid chromatography with UV-Vis detection. The samples were transferred onto a C18 solid-phase extraction column and chromatographed on a Hypersil ODS RP C18, 5 microns (250 x 4 mm I.D.) with an acetonitrile-water elution gradient containing propylamine. Under these conditions, the amines are eluted with a short retention time. The procedure has been applied to the determination of amphetamine and methamphetamine in the range 0.3-4.0 micrograms/ml in spiked urine samples. The detection limits at 280 nm were 4 and 2 ng/ml for amphetamine and methamphetamine, res…
A clean method for flow injection spectrophotometric determination of cyclamate in table sweeteners
2005
Abstract A flow system based on the multicommutation is proposed for fast and clean determination of cyclamate. The procedure exploits the reaction of cyclamate with nitrite in acidic medium and the spectrophotometric determination of the excess of nitrite by iodometry. The flow system was designed with a set of solenoid micro-pumps to minimize reagent consumption and waste generation. The detection limit was estimated as 30 μmol L −1 (99.7% confidence level) with linear response ranging up to 3.0 mmol L −1 . The coefficient of variation was estimated as 1.7% for a solution containing 2.0 mmol L −1 cyclamate ( n = 20). About 60 samples can be analyzed per hour, consuming only 3 mg KI and 1…
An environmentally friendly multicommutated alternative to the reference method for anionic surfactant determination in water
2004
Abstract It has been developed a fully mechanized procedure for the spectrophotometric determination of anionic surfactants in water expressed in terms of SDS concentration. The reference method, based on the reaction of SDS with methylene blue (MB) followed by extraction in chloroform, was mechanized in order to reduce the consumption of organic solvents. The system was based on the multicommutation approach and provided a 35 times reduction of the waste production without sacrificing the figures of merit of the method in terms of sensitivity and repeatability, for a dynamic linear range from 0.2 to 1.7 mg l−1. Results obtained for washing water samples were comparable with those obtained …
Flow analysis-spectrophotometric determination of ?-dopa in pharmaceutical formulations by reaction with p-Aminophenol
1994
Abstract A new method has been developed for the spectrophotometric determination of l -dopa in pharmaceutical formulations. The method is based on the reaction between the open-chain quinone of l -dopa, obtained in NaOH, and the benzoqinoneimine form of p-aminophenol, in the presence of KIO4. The reaction product is determined at 574 nm by using both alternately procedures, one based on the stopped-flow and another on a flow injection approach. Under the best experimental conditions L-dopa can be determined with a limit of detection of 52 ng/ml and a relative standard deviation of 0.2% for three replicate measurements of a solution containing 4 μg/ml.
Direct derivative spectrophotometric determination of carbaryl and carbofuran in water samples
1990
Abstract Derivative absorption spectrophotometry has been applied to the direct determination of carbaryl and carbofuran in water samples. The use of the third derivative for carbaryl and the fourth derivative for carbofuran reduces the matrix effect and the seventh derivative provides, in both cases, accurate results for the determination of these pesticides, even working at low dilution levels of the samples. A limit of detection of 4 ppb and a variation coefficient of 0.1% have been obtained for the determination of carbaryl. Carbofuran can be determined with a limit of detection of 5 ppb and a variation coefficient of 0.02%.
Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol
1992
Abstract An automated procedure has been developed for the determination of formetanate and its metabolite m -aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p -aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO 4 , as oxidizing agent. The method has a limit of detection of 5 × 10 −7 M , it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessa…
Spectrophotometric determination of phenol and resorcinol by reaction with p-aminophenol
1993
Abstract Based on the reaction with p-aminophenol, a series of procedures have been developed for the spectrophotometric determination of phenol and resorcinol. Three basic approaches have been studied: (i) a batch procedure, using the dissolved oxygen as oxidant, (ii) a stopped-flow procedure by use of KIO4 as oxidant and (iii) a flow injection (FI) procedure developed in the presence of KIO4. Phenol can be accurately determined at 626 nm, in the stopped-flow mode, after a reaction time of 45 min in 0.005M NaOH, 0.004M KIO4 and 500 μg/ml of PAP. The development of a manifold, which incorporates a sample parking, is a convenient approach which makes it possible to measure, in the stopped-fl…