Search results for "Reagent"
showing 10 items of 699 documents
Microwave-assisted saponification of animal greases for cholesterol determination
1998
Abstract An alternative method for the hydrolysis of cholesterol esters in animal grease samples has been developed. The method consists of the microwave-assisted treatment of 4 g of animal fat or oil with 40 ml of an ethanolic KOH solution inside a 115 ml closed reactor in which samples were irradiated for 2.5 min at 50% power level of an exit power of 700 W. After extraction with petroleum ether and dissolution of the unsaponifiables in toluene, total cholesterol was determined spectrophotometrically by using p-anisidine as a test reagent of the enzymatic reaction of cholesterol through a bienzymic reactor in which cholesterol oxidase and horseradish peroxidase were noncovalently immobili…
Sequential injection analysis for benzophenone-4 and phenylbenzimidazole sulphonic acid in sunscreen sprays by solid-phase extraction coupled with ul…
2002
Abstract A sequential injection UV method was developed to determine benzophenone-4 (BZ4) and phenylbenzimidazole sulphonic acid (PBS) simultaneously, these being the most commonly used UV-filters in aqueous formulations used as sunscreen sprays. The selective elution of both was performed by on-line solid-phase extraction, by retention on a SAX microcolumn and separation by varying the pH of elution. The sensitivity obtained was 0.042±0.001 ml μg −1 for PBS and 0.0159±0.0003 ml μg −1 for BZ4. The limit of detection was 1.6 μg ml −1 for PBS and 0.6 μg ml −1 for BZ4. The R.S.D. of the results was 1–6% for PBS and 1–12% for BZ4. The method was validated using commercial sunscreen formulations…
Improvement of the atomic fluorescence determination of mercury by using multicommutation
2002
Atomic fluorescence spectrometry (AFS) determination of Hg has been improved by exploiting the possibilities of the multicommutation approach in order to outline a fully mechanised system which supplies the same sensitivity as the use of continuous measurements, reducing drastically the reagents consumed and waste generation. The use of multicommutation with a simultaneous reduction of the liquid–gas separator volume and the insertion point modification of argon transport gas provides a sensitivity of the AFS measurements of 300 mV ng−1 ml (using a full scale of 1000 mV), a limit of detection (3 s) of 1.3 ng l−1 and relative standard deviation values below 0.1% for 10 independent measuremen…
Flow injection spectrophotometric determination of boron in ceramic materials.
1998
Abstract A flow injection spectrophotometric method for the determination of boron in ceramic materials is described. The method is based on spectrophotometric measurement of the decrease in the pH produced by the reaction between boric acid and mannitol in the presence of an acid-base indicator. A bichannel FI (flow injection) manifold in which the sample solutions were injected into deionized water (at pH 5.4) and the stream was later merged with the reagent stream (a mannitol solution containing 1×10 −4 mol l −1 bromocresol green at pH 5.4), was used. Transient signals were monitored at 616 nm. A theoretical model which describes the dependence between the absorbance values and boric aci…
Contribution to the adsorption voltammetric determination of manganese
1994
The adsorption voltammetric determination of Mn(II) with Bromopyrogallol Red (BPR) and Mordant Red 19 (MDR) has been investigated using a hanging drop mercury electrode. In NH3/NH4Cl solution, ligands and Mn(II) complexes give well separated voltammetric peaks after enrichment onto the electrode. The conditions for determining manganese by adsorption voltammetry with these reagents have been investigated in detail, as has the influence of foreign ions on the determination. The detection limits are 4·10−10 mol/L Mn for BPR and 8·10−10 mol/L Mn for MDR, respectively.
Urine polyamines determination using dansyl chloride derivatization in solid-phase extraction cartridges and HPLC
1999
The derivatization of biogenic amines such as putrescine, cadaverine, spermidine and spermine with dansyl chloride in solid phase extraction cartridges is described. Different types of filling materials were tested in order to have the highest retention of the different analytes. The best results were obtained by using C18 cartridges. The optimal conditions were: amine solution buffered at pH 12, 2 mM dansyl chloride (acetone-bicarbonate solution 20 mM (pH 9-9.5), 2 + 3 v/v) as reagent concentration, room temperature and 30 min reaction time. The developed procedure was applied to the determination of these polyamines in urine samples from healthy controls and cancer patients using HPLC wit…
New flow-multicommutation method for the photo-chemiluminometric determination of the carbamate pesticide asulam
2004
This paper deals with a straightforward automated method for the determination of asulam in water based on the use of a flow manifold including three computer-controlled solenoid valves. The method involves irradiating on an aqueous solution of asulam in glycine buffer at pH 8.3 with UV light during 90 s, then follows the oxidation with potassium permanganate in a sulphuric medium and chemiluminescence-based detection of the resulting photoproducts. The limit of detection thus achieved is 40 mug l(-1). The detector response is linear up to a 5 mg l(-1) asulam concentration and the throughput is 30 samples h(-1). In parallel tests, oxidation with alkaline ferricyanide was also assessed and t…
A portable and low cost equipment for flow injection chemiluminescence measurements.
2004
A compact, reliable and low cost flow injection chemiluminescence system is described. The flow system consists of a set of solenoid micro-pumps that can dispense reproductive micro-volumes of solutions. The luminometer was based on a coiled cell constructed from polyethylene tubing that was sandwiched between two large area photodiodes. The whole equipment costs about US$ 750 and weights ca. 3 kg. Equipment performance was evaluated by measuring low concentrations of hydrogen peroxide by oxidation of luminol and for the determination of ammonium, based on its inhibition of the luminescence provided by the reaction of luminol and sodium hypochlorite. Linear responses were achieved within 1.…
Vibrational Spectrometry Strategies for Quality Control of Procymidone in Pesticide Formulations
2005
Abstract Two vibrational spectrometry–based methodologies were developed for procymidone determination in wettable powdered pesticide formulations. The Fourier‐transform infrared (FTIR) procedure was based on the selective extraction of procymidone by chloroform and determination by peak area measurement between 1451 and 1441 cm−1, using a baseline correction established between 1490 and 1410 cm−1, and a precision of 0.4% and a limit of detection of 0.01% w/w procymidone for a sample mass of 25 mg were obtained. For FT‐Raman determination, the selected conditions were peak area measurement between 1005 and 995 cm−1 Raman shift, with a baseline correction fixed between 1030 and 947 cm−1, and…
Automated Fourier Transform near Infrared Determination of Buprofezin in Pesticide Formulations
2005
An automated procedure has been developed for Fourier transform near infrared (FT-NIR) determination of buprofezin in pesticide formulations. This methodology is based on on-line pesticide extraction with acetonitrile from solid samples and its determination by using peak area absorbance measurements between 2147 and 2132 nm, corrected with a horizontal baseline established at 2091 nm. The repeatability, as a relative standard deviation of five independent analyses of 18.9 mg g−1 of buprofezin, was 0.06% and the limit of detection 5 mg L−1. The reagent consumption was clearly reduced compared with a chromatographic reference procedure from 40.4 mL acetonitrile per sample, required by high …