Search results for "Spectrophotometry"
showing 10 items of 644 documents
Rapid microwave assisted hydrolysis of formetanate
1993
Abstract A fast microwave-assisted hydrolysis procedure has been developed for the derivatization of formetanate previously to the flow-injection spectrophotometric determination of m -aminophenol by reaction with p -aminophenol. Formetanate is quantitatively hydrolyzed with 0.1 M NaOH in 150 s using a closed polyetrafluoroethylene reactor with 115 ml internal volume and a radiation power of 390 W. The above procedure has been applied, as a previous step, for the flow-injection spectrophotometric determination of formetanate in spiked water samples and accurate and precise results have been found. The method permits to obtain a limit of detection of 0.025 mg 1 −1 of formetanate. The relativ…
A rapid and reliable size-exclusion chromatographic method for determination of kojic dipalmitate in skin-whitening cosmetic products
2007
A size-exclusion chromatographic method has been developed to determine the relatively novel skin-whitening agent called kojic dipalmitate (KDP) in skin-whitening cosmetic products. Preliminary experiments were carried out in order to select the solvent for standard and sample solution, and also for mobile phase composition. A PLGel Mixed-D (polystyrene/divinylbenzene co-polymer) column and isocratic mobile phase of pure tetrahydrofuran (at 1.5 mL min(-1) flow rate) were used. Detection was carried out by means of an UV/vis spectrometry detector set at 248 nm. A study of interferences reveals that KDP can be determined without interferences coming from cosmetic matrices. Most other cosmetic…
Extractive-spectrophotometric determination of amphetamine in urine samples with sodium 1,2-naphthoquinone 4-sulphonate
1993
Abstract Sodium 1,2-naphthoquinone 4-sulphonate (NQS) was tested as a reagent for amphetamine in order to develop an extractive-spectrophotometric method for the drug in urine samples. The standard additions method showed the absence of proportional bias error whereas the Youden method and the two standard addition plots method showed the presence of a constant bias error [total Youden blank (TYB)]. Acceptable results were obtained by evaluating the TYB error or by using a placebo (urine sample from a normal subject). The dynamic range of concentrations was 1.4–50 mg 1−1 in urine samples and the detection limit was 0.6 mg 1−1 when 10 ml of urine sample were taken.
Determination of catecholamines as aminochromes by micellar liquid chromatography with thermal lens spectrophotometric detection
1994
The determination of catecholamines (CAs) using micellar liquid chromatography with thermal lens spectrophotometric detection has been studied. CAs are oxidized with hexacyanoferrate(III) to aminochromes which are separated with a mobile phase of 0.05 M sodium dodecyl sulphate, 7% propanol and 0.03 M citrate buffer, pH 4.8, on a partially endcapped C18 column. The aminochrome-micelles and aminochrome-stationary phase association constants are evaluated. Using the 488 nm line of an Ar+ laser with 250 mW pump power the limits of detection are about 4 ng mL−1. The technique is applied to the determination of unconjugated CAs in urine using isoproterenol as internal standard.
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 determination of free and total cholesterol in animal greases using enzymes in non-aqueous media
1998
A non-covalently coimmobilized bienzymic reactor of horseradish peroxidase (HRP) and cholesterol oxidase (COD), operating in a continuous organic flowing stream of 1 × 10–3 M p-anisidine in buffer-saturated (pH 7.0) toluene, has been employed for cholesterol determination in animal greases, such as pig, beef, and chicken fat, and codfish liver oil. The method provides a good linear relationship up to 1.8 × 10–3 M cholesterol and average recoveries of 99.5%, a high sensitivity, with a detection limit of 1 × 10–6 M of cholesterol and a good precision (an interday RSD of 1.8% for the determination of total cholesterol in a codfish oil sample). The method permits the direct spectrophotometric d…
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…
A multicommuted flow system with solenoid micro-pumps for paraquat determination in natural waters.
2007
A flow system designed with solenoid micro-pumps is proposed for the determination of paraquat in natural waters. The procedure involves the reaction of paraquat with dehydroascorbic acid followed by spectrophotometric measurements. The proposed procedure minimizes the main drawbacks related to the standard chromatographic procedure and to flow analysis and manual methods with spectrophotometric detection based on the reaction with sodium dithionite, i.e. high solvent consumption and waste generation and low sampling rate for chromatography and high instability of the reagent in the spectrophotometric procedures. A home-made 10-cm optical-path flow cell was employed for improving sensitivit…
o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine
2002
A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent…
Optimization of clean-up procedure for patulin determination in apple juice and apple purees by liquid chromatography
2009
Patulin (PAT) is a mycotoxin produced in fruits, mainly in apples, by several fungal species that can be carried into industrial apple juice by-products during factory processing. An analytical method for determination of PAT in apple juice and another one for determination of this compound in apple purees and apple compotes by liquid chromatography are proposed in the present paper. These methods have better precision and sensitivity than previously reported methods and focus mainly on extraction and clean-up. To accomplish analytical methods with higher accuracy, lower limits of detection and simpler procedures for application in quality control of the goods, different extraction and clea…