Search results for "Absorbance"
showing 10 items of 192 documents
Simultaneous determination of Folpet and Metalaxyl in pesticide formulations by flow injection Fourier transform infrared spectrometry
2003
Fourier transform infrared (FTIR) spectrometric methodology has been developed for the simultaneous determination of Folpet and Metalaxyl in pesticide formulations. The method involves the extraction of both active principles by sonication of the sample with CHCl3 and direct measurement of the absorbance using peak height values at 1798 cm −1 corrected with a baseline defined at 1810 cm −1 for Folpet, and peak area data established from 1677 to 1667 cm −1 corrected using a baseline from 1692 to 1628 cm −1 for Metalaxyl. Limits of detection (3 s) values of 17 and 16 gg −1 were found for Folpet and Metalaxyl, respectively, with results comparable with those found by liquid chromatography with…
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 vapor generation Fourier transform infrared spectrometric determination of ethanol in blood
1996
Abstract A new procedure is proposed for a direct determination of ethanol in plasma and whole blood. The method is based on the injection of a discrete sample volume of 10 μl into an electrically heated Pyrex glass reactor in which, at a temperature of 90 °C, the ethanol is volatilized and introduced by means of a N 2 carrier flow inside a long-path infrared gas cell and the corresponding flow analysis recording registered as a function of time. The measurement of the area of the flow injection recording, obtained from the absorbance of the transient signal in the range 1150−950 cm −1 , allows the direct quantification of ethanol upto 2 g l −1 , with a limit of detection of 0.020 g l −1 an…
Flow-injection spectrophometric determination of propoxur with p-aminophenol
1992
Abstract The spectrophotomeric determination of propoxur [2-(1-methyxlthoxy)phenyl methyl carbamate] was carried out with p -aminophenol (PAP) in a flow system. The method involves the on-line hydrolysis with NaOH of propoxur to 2-isopropoxyphenol and the oxidation of PAP to its relative quinone imine with KIO 4 and the reaction between the phenolate and the quinone imine. A four-channel flow manifold was employed to carry out all the different steps of the reaction considered, monitoring the indo dye formed at 600 nm. The developed procedure provides a typical calibration line of A = 0.000 7 + 1.8 × 10 3 C ( A = absorbance; C = concentration in M) with a regression coefficient of 0.9998 an…
Determination of caffeine in tea samples by Fourier transform infrared spectrometry
2002
A sustainable and environmentally friendly procedure has been developed for the FTIR determination of caffeine in tea leaf samples. The method is based on the extraction with ammonia and CHCl3 and direct determination of caffeine on the chloroform extracts using peak height absorbance measurements at 1658.5 cm(-1) and external calibration. The method provides a sensitivity of 0.2142 absorbance units mg(-1) mL and a limit of detection of 1 mg L(-1), corresponding to 0.002% m/m caffeine in tea leaves. As compared with a reference procedure, based on UV absorbance measurement at 276 nm after low pressure column chromatography, the developed procedure reduces the consume of CHCl3 by a factor of…
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…
HPLC determination of oxadiazon in commercial pesticide formulations
2008
A simple, fast and precise high performance liquid chromatographic (HPLC) procedure has been developed for the determination of oxadiazon in emulsifiable concentrated pesticide formulations. 20 µL of diluted sample in acetonitrile were injected in a Kromasil C18 (250 ×am injetados em uma coluna Kromasil C18 4.6 mm, 5 µm) column, using acetonitrile:water (80:20) as mobile phase at 1 mL min-1 flow rate and oxadiazon determined by absorbance measurement at 292 nm. A theoretical limit of detection of 0.02 µg mL-1, a limit of quantification of 0.047 µg mL-1, corresponding to a 0.02 and 0.07% m/v in the original sample, and a relative standard deviation of 0.08% for three replicate analysis of sa…
Flow injection Fourier transform infrared determination of caffeine in coffee
1999
Abstract A fully automatized procedure has been developed for the Fourier transform infrared (FT-IR) spectroscopic determination of caffeine in coffee samples. The method involves the on-line extraction of caffeine with CHCl3. Samples, weighed inside empty PTFE cartridges of 0.5 cm internal diameter (i.d.) and 1.5 ml volume, were humidified with four drops of 0.25 M NH3. The cartridge was installed in a flow manifold, in which samples were extracted in a closed-flow system with 1 ml CHCl3 during 6 min. Four hundred microliters of the extract were introduced in a microflow cell and absorbance measured as a function of time at 1659 cm−1, with a baseline established between 1900 and 830 cm−1, …
Flow injection-spectrophotometric determination of cresol compounds in water by reaction withp-aminophenol
1993
A spectrophotometric method has been developed for the simultaneous determination ofo-cresol andm-cresol in water by reaction withp-aminophenol (PAP). Three different methodologies have been assayed; (i) batch analysis, after reaction in an alkaline medium in the presence of dissolved molecular oxygen as oxidizing agent, (ii) a stopped-flow procedure, carried out in the presence of KIO4 and (iii) a flow injection method based on the same approach. The batch procedure requires 22 min for the full development of colour witho-cresol and 12 min form-cresol. In the stopped-flow mode, using KIO4 and a reaction time of 12 min, better sensitivity can be obtained for both compounds and limits of det…
Flow injection flame atomic spectrometric determination of iron, calcium, magnesium, sodium and potassium in ceramic materials by using a variable-vo…
1993
A series of different ceramic materials, such as porcelain, feldspar, kaolin, varnish, clay and stoneware have been analyzed. Iron, calcium and magnesium have been determined in these materials by flame atomic absorption and sodium and potassium by flame emission. The use of a variable-volume injector enables one to carry out these analyses in a flow system (after fusion of samples with lithium metaborate) and does not require different dilutions for the determination of each type of sample considered, nor the use of different flow injection manifolds. The developed procedure provides a limit of detection of 100 μg/l for Na, 70 μg/l for Ca, 50 μg/l for both Fe and K and 8 μg/l for Mg. The c…