Search results for "Photometry"
showing 10 items of 797 documents
Determination of aniline in vegetable oils by diazotization and coupling in a microemulsion medium
1990
Abstract A microemulsion containing sodium dodecyl sulphate and n -pentanol in a mass ratio of 1 : 4, water and a vegetable oil was investigated using pseudo-tenary phase diagrams. The medium can co-solve important amounts of vegetable oils and aqueous solutions over a wide range of ionic strengths. A procedure for the determination of 1.4–140 μg ml −1 of aniline in vegetable oils using ionic diazotization and coupling reactions was developed. The absorbance was measured in an optically clear microemulsion containing 4% or 20% of oil. The procedure is much simpler and rapid than the official chromatographic methods and gives almost the same limits of detection (ca. 05 μg ml −1 ) using no mo…
Sequential injection spectrophotometric determination of oxybenzone in lipsticks
2001
A sequential injection (SI) procedure for the spectrophotometric determination of oxybenzone in lipsticks is reported. The colorimetric reaction between nickel and oxybenzone was used. SI parameters such as sample solution volume, reagent solution volume, propulsion flow rate and reaction coil length were studied. The limit of detection was 3 microg ml(-1). The sensitivity was 0.0108+/-0.0002 ml microg(-1). The relative standard deviations of the results were between 6 and 12%. The real concentrations of samples and the values obtained by HPLC were comparable. Microwave sample pre-treatment allowed the extraction of oxybenzone with ethanol, thus avoiding the use of toxic organic solvents. E…
Simultaneous determination of olanzapine, clozapine and demethylated metabolites in serum by on-line column-switching high-performance liquid chromat…
2001
An automated method for simultaneous routine quantification of the antipsychotic drugs clozapine, olanzapine and their demethylated metabolites is described. The method included adsorption on a cyanopropyl (CPS) coated clean-up column (10 microm; 10 x 2.0 mm I.D.), washing off interfering serum constituents to waste, and separation on C18 ODS Hypersil reversed phase material (5 microm; 250 x 4.6 mm I.D.) using acetonitrile-water-tetramethylethylenediamine (37:62.6:0.4, v/v/v) adjusted to pH 6.5 with concentrated acetic acid. UV-detection was performed at 254 nm. The limit of quantification was 10-20 ng/ml. Relative day to day standard variations ranged between 4.5 and 13.5%. The method is s…
Solid-Phase Microextraction Liquid Chromatography/Tandem Mass Spectrometry To Determine Postharvest Fungicides in Fruits
2003
A method to determine five postharvest fungicides (dichloran, flutriafol, o-phenylphenol, prochloraz, tolclofos methyl) in fruits (cherries, lemons, oranges, peaches) has been developed using solid-phase microextraction (SPME) coupled to liquid chromatography (LC) with photodiode array (DAD), mass spectrometry (MS), or tandem mass spectrometry (MS/MS) with ion trap detection. Extraction involved sample homogenization with an acetone/water solution (5:1), filtration, and acetone evaporation prior to fiber extraction. The pesticides were isolated with a fused-silica fiber coated with 50-microm Carbowax/template resin. The effects of pH, ion strength, sample volume, and extraction time were in…
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 …