Search results for "LIMIT"
showing 10 items of 2826 documents
Chromium speciation using activated alumina microcolumns and sequential injection analysis-flame atomic absorption spectrometry
2001
Abstract A new procedure has been developed for chromium speciation in water by sequential injection analysis and flame atomic absorption spectrometry. The method involves the online retention of Cr(VI) anionic species and Cr(III) cationic species on alumina microcolumns, prepared by packing activated alumina in polytetrafluoroethylene tubes, followed by selective elution of Cr(VI) with 2 mol l −1 NH 4 OH and of Cr(III) with 0.2 mol l −1 HNO 3 . Studies were carried out on the effect of retention and elution conditions for both Cr species. The limit of detection values, established as the concentration corresponding to three times the standard deviation of blank measurements divided by the …
Determination of N-nitrosodiethanolamine in cosmetic products by reversed-phase dispersive liquid-liquid microextraction followed by liquid chromatog…
2016
A new analytical method for the determination of N-nitrosodiethanolamine (NDELA), a very harmful compound not allowed in cosmetic products, is presented. The method is based on a new approach of dispersive liquid-liquid microextraction (DLLME) useful for extraction of highly polar compounds, called reversed-phase DLLME (RP-DLLME), followed by liquid chromatography-ultraviolet/visible (LC-UV/Vis) determination. The variables involved in the RP-DLLME process were studied to provide the best enrichment factors. Under the optimized conditions, a mixture of 750µL of acetone (disperser solvent) and 125µL of water (extraction solvent) was rapidly injected into 5mL of toluene sample solution. The e…
Preconcentration and dansylation of aliphatic amines using C18 solid-phase packings
2002
Abstract Precolumn preconcentration and derivatization on solid sorbents (Bond Elut C18 solid-phase extraction cartridges) of low-molecular-mass aliphatic amines in water samples have been performed using dansyl chloride (Dns-Cl) as derivatization reagent. Conditions for analyte preconcentration and derivatization such as volume sample, reagent concentration, time, pH and temperature reaction were optimised. On the basis of these studies a rapid and sensitive method for screening of aliphatic amines in waters is presented. Up to volumes of 5 ml, samples are drawn through the sorbent, the analytes retained are dansylated at basic pH, at 100 °C for 10 min or 85 °C for 15 min. The derivatized …
Die direkte quantitative auswertung von dünnschichtchromatogrammen durch remissions- und fluoreszenzmessungen
1971
Abstract Direct quantitative evaluation of thin-layer chromatograms by remission- and fluorescence measurements. Part 6. Determination of adrenaline, noradrenaline and dopamine from urine Adrenaline, noradrenalineand dopamine were separated from urine on aluminium oxide columns; after elution they were converted into ther O 3 ,O 4 ,N-triacetyl derivatives and separated using thin-layer chromatography. The triacetyl derivatives were in situ converted to fluorescing compounds using ethylene diamine and quantitatively estimated using the Chromatogram-Spectrophotometer (Carl Zeiss, Oberkochen). The advantage of this method over the conventional fluorometric determination of catecholamines in so…
Univariate near infrared methods for determination of pesticides in agrochemicals
2006
Abstract It has been developed a general strategy for the determination of pesticides in agrochemicals by Fourier transform near infrared (FT-NIR) spectroscopy. The methodology is based on previous extraction of the active principles through sonication with acetonitrile and direct determination by transmission measurements, using glass vials as measurement cells and univariate calibration at selected wavenumbers as a function of the pesticide to be analyzed. Chlorsulfuron, metamitron, iprodione, pirimicarb, procymidone and tricyclazole were used as test molecules and data obtained by FT-NIR for 20 samples containing one of these active principles compare well with those found by reference l…
Determination of cyromazine in pesticide commercial formulations by vibrational spectrometric procedures
2004
Two vibrational spectrometry-based methodologies were developed for Cyromazine determination in solid pesticide formulations: a Fourier transform infrared (FTIR) procedure, based on the extraction of Cyromazine by CH3OH and direct determination in the extracts by peak height measurement at 1622 cm−1 corrected using a baseline defined at 1900 cm−1, and a FT-Raman determination, made directly on the powdered solid products using standard chromatographic glass vials as sample cells and measuring the Raman intensity between 633 and 623 cm−1 for a baseline established between 663 and 601 cm−1. The sensitivity obtained was 0.01631 absorbance g−1 mg for FTIR determination and 2.23 area values g−1 …
Direct injection of edible oils as microemulsions in a micellar mobile phase applied to the liquid chromatographic determination of synthetic antioxi…
1999
Abstract A simple and quick procedure for analysis of hydrophobic samples by direct injection in a liquid chromatograph, without previous extraction, has been developed. The sample is solved in a water/sodium dodecyl sulphate/n-pentanol microemulsion without destroying the microemulsion structure, and injected. A micellar mobile phase containing 0.1 M SDS, 2.5% n-propanol and 10 mM phosphate of pH 3 is used. The procedure is applied to the determination of synthetic antioxidants (propyl gallate, tert-butylhydroquinone, 2,4,5-trihydroxybutyrophenone, nordihydroguaiaretic acid, octyl gallate, 3-tert-butyl-4-hydroxyanisole and dodecyl gallate) in sunflower, corn and olive oils. Linear calibrat…
Application of ACC method to synchronous luminiscence: determination of alpha-tocopherol and alpha-tocopheryl acetate in beverages.
2001
A new method based on the Q parameter, that permits the determination of the C(compound A)/C(compound B) ratio without preparing calibration graphs of the two compounds, is proposed. This method has been applied to signals obtained by synchronous luminiscence. Simultaneous determination of alpha-tocopherol and alpha-tocopheryl acetate in beverages using synchronous fluorescence has been carried out. To isolate the compounds from samples, liquid extraction with n-hexane as the organic phase was employed. The presence of interferences was tested using the apparent content curves (ACC) method and the C(alpha-tocopherol)/C(alpha-tocopheryl acetate) ratio was calculated using the Q parameter. Th…
Changes in yield ofin-vivo fluorescence of chlorophyll a as a tool for selective herbicide monitoring
1993
Triazines and derivatives of phenylurea, which are often found in outdoor water samples, induce specific changes in the yield of thein-vivo chlorophyll α-fluorescence of PSII. These changes are correlated quantitatively with the concentration of the herbicides and can therefore be used to set-up a low-price monitor system. In order to detect selectively the herbicide-sensitive part of the fluorescence emission a pulse amplitude modulated fluorimeter was used. The bioassay system was optimised with respect to test organism, growing and measuring conditions. The relationship between fluorescence yield and herbicide concentrations were experimentally determined for the triazines atrazine and s…
Enhanced flow-injection–chemiluminometric determination of sulphonamides by on-line photochemical reaction
2003
Abstract The viability of the tandem photochemical reaction-chemiluminescence detection has been studied for an heterogeneous group of sulphonamides (sulphamethoxazole, sulphadiazine, sulphamerazine, sulphamethoxypyridazine, sulphacetamide, sulphadimidine, sulphanilamide, sulphathiazole and sulphaguanidine) using sulphamethoxazole (whose chemiluminescent behaviour has not been previously reported) as a test substance. The ‘on-line’ photochemical-reaction of sulphonamides provides an enhancing influence on the chemiluminometric response of the drugs during their oxidation by potassium permanganate in sulphuric acid medium (sulphamethoxazole, sulphacetamide, sulphadimidine and sulphanilamide …