Search results for "Detection limit"
showing 10 items of 810 documents
Fishing for a drug: solid-phase microextraction for the assay of clozapine in human plasma
1999
Solid-phase microextraction (SPME) was investigated as a sample preparation method for assaying the neuroleptic drug clozapine in human plasma. A mixture of human plasma, water, loxapine (as internal standard) and aqueous NaOH was extracted with a 100-micron polydimethylsiloxane (PDMS) fiber (Supelco). Desorption of the fiber was performed in the injection port of a gas chromatograph at 260 degrees C (HP 5890; 30 m x 0.53 mm I.D., 1 micron film capillary; nitrogen-phosphorous selective detection). Fibers were used repeatedly in up to about 75 analyses. The recovery was found to be 3% for clozapine from plasma after 30 min of extraction. However, in spite of the low recovery, the analyte was…
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 …
Comparison of direct mass spectrometry methods for the on-line analysis of volatile compounds in foods
2013
For the on-line monitoring of flavour compound release, atmospheric pressure chemical ionization (APCI) and proton transfer reaction (PTR) combined to mass spectrometry (MS) are the most often used ionization technologies. APCI-MS was questioned for the quantification of volatiles in complex mixtures, but direct comparisons of APCI and PTR techniques applied on the same samples remain scarce. The aim of this work was to compare the potentialities of both techniques for the study of in vitro and in vivo flavour release. Aroma release from flavoured aqueous solutions (in vitro measurements in Teflon bags and glass vials) or flavoured candies (in vivo measurements on six panellists) was studie…
Interaction of diazepam with surfactants. Spectrophotometric and spectrofluorometric study
1986
Abstract The interaction of diazepam with non-ionic, anionic and cationic surfactants has been studied spectrophotometrically and fluorometrically. It has been verified that the absorption spectrum of diazepam is not modified in micellar medium. However, a dramatic five-fold increase in fluorescence sensitivity is observed in the presence of sodium lauryl sulphate (SDS). The experimental conditions, temperature, pH and surfactant concentration have been optimized to improve the fluorometric determination of diazepam and a detection limit of 0,04 ppmhas been obtained.
Theoretical prediction of the chemiluminescence behaviour of the ergot alkaloids
2004
Abstract The present manuscript is dealing with the application of molecular connectivity calculations to predict the chemiluminescent behaviour of ergot alkaloids when they react with common strong oxidants in liquid phase. Twenty compounds were theoretically studied by means of a discriminant equation formerly published, being 19 of them predicted as chemiluminescent with a high probability. Empirical confirmation of the chemiluminometric behaviour is performed with the few soluble and commercially available ergot alkaloids. On the basis of these results, a new FIA-direct chemiluminescent method is proposed for the determination of the ergot presenting the higher light emission, the pharm…
Direct determination of benzene in gasoline by flow-injection Fourier transform infrared spectrometry
1993
Abstract A Fourier transform infrared spectrometric procedure for the automated determination of benzene in gasoline was developed, based on the use of flow-injection analysis. The method permits the direct determination of benzene without any pretreatment of samples, with a limit of detection of 0.02% (v/v) and a relative standard deviation of ca. 1% [for five independent analyses of a diluted sample containing a 0.4% (v/v) of benzene]. Results found by direct analysis agreed with those obtained by off-line and on-line standard addition methods. A rapid quality control procedure was developed, based on the on-line injection of gasoline samples (diluted 1 + 9 in hexane) into a carrier strea…
Determination of edible oil parameters by near infrared spectrometry
2006
Abstract A chemometric method has been developed for the determination of acidity and peroxide index in edible oils of different types and origins by using near infrared spectroscopy (NIR) measurements. Different methods for selecting the calibration set, after an hierarchical cluster analysis, were applied. After discrimination of olive oils from maize, seed and sunflower, the prediction capabilities of partial least squares (PLS) multivariate calibration of NIR data were evaluated. Several preprocessing alternatives (first derivative, multiplicative scatter correction, vector normalization, constant offset elimination, mean centering and standard normal variate) were investigated by using…
Determination of thyreostatics in animal feed by micellar electrokinetic chromatography
1999
The determination of the thyreostatics 2-thiouracil, its derivatives (4-methyl-2-thiouracil, 4-propyl-2-thiouracil and 4-phenyl-2-thiouracil) and methimazole in manufactured dried animal feed by micellar electrokinetic chromatography (MEKC) is described. A 99 +/- 5% extraction yield at the 20 micrograms g-1 level (n = 8) was achieved by shaking the milled fodder with methanol-1 M NaOH (80 + 20). Aliquots of the supernatant were injected in a 75 microns x 33.5 cm uncoated silica capillary using pressure; separation was performed at 23 degrees C with 15 kV (positive polarity) in a background electrolyte (BGE) containing 40 mM sodium dihydrogenphosphate, 50 mM sodium dodecyl sulfate and 15 mM …
A simple novel configuration for in-vial microporous membrane liquid–liquid extraction
2009
Abstract A novel arrangement for microporous membrane liquid–liquid extraction from the aqueous donor phase to the organic acceptor phase within a micro-vial, which is compatible with the chromatograph autosampler is presented. The device consisted of a stoppered glass micro-vial containing the organic solvent where the septum of the screw stopper was replaced by a sized piece of membrane which is hermetically assembled to the volumetric flask containing the aqueous donor solution. The placement of the membrane in alternative contact with the solutions was achieved by orbital agitation. As a preliminary study, 2-ethylhexyl 4-(dimethylamino)benzoate has been determined (limit of quantificati…
Determination of water-soluble UV-filters in sunscreen sprays by liquid chromatography.
2002
Abstract Liquid chromatography was used for the determination of the three most used water-soluble UV filters, benzophenone-4 (BZ4), terephthalylidene dicamphor sulfonic acid (TDS), and phenylbenzimidazole sulphonic acid (PBS), in aqueous sunscreen sprays. A C 18 stationary phase and an isocratic mobile phase of EtOH–20 m M sodium acetate buffer of pH 4.6 (30:70, v/v) were used at a flow-rate of 0.5 ml min −1 . Mobile phase was also used as solvent for samples and standards. UV detection was at 313 nm. The analytical run took 5.5 min. The limits of detection were 0.5, 0.9 and 2 μg ml −1 for BZ4, TDS and PBS, respectively. The proposed method does not involve highly toxic solvents.