Search results for "liquid"
showing 10 items of 4351 documents
Determination of alternative preservatives in cosmetic products by chromophoric derivatization followed by vortex-assisted liquid-liquid semimicroext…
2016
An analytical method for the simultaneous determination of phenethyl alcohol, methylpropanediol, phenylpropanol, caprylyl glycol, and ethylhexylglycerin, which are used as alternative preservatives in cosmetic products, has been developed. The method is based on liquid chromatography with UV spectrophotometric detection after chromophoric derivatization with benzoyl chloride and vortex-assisted liquid-liquid semimicroextraction. Different chromatographic parameters, derivatization conditions, and sample preparation variables were studied. Under optimized conditions, the limits of detection values for the analytes ranged from 0.02 to 0.06µgmL(-1). The method was validated with good recovery …
Sensitive determination of parabens in human urine and serum using methacrylate monoliths and reversed-phase capillary liquid chromatography-mass spe…
2014
A method for the determination of parabens in human urine and serum by capillary liquid chromatography (cLC) with UV-Vis and mass spectrometry (MS) detection using methacrylate ester-based monolithic columns has been developed. The influence of composition of polymerization mixture was studied. The optimum monolith was obtained with butyl methacrylate monomer at 60/40% (wt/wt) butyl methacrylate/ethylene dimethacrylate ratio and 50wt% porogens (composed of 36wt% of 1,4-butanediol, 54wt% 1-propanol and 10wt% water). Baseline resolution of analytes was achieved through a mobile phase of acetonitrile/water in gradient elution mode. Additionally, dispersive liquid-liquid microextraction (DLLME)…
Determination of phenolic antioxidants in vegetal and animal fats without previous extraction by dilution with n-propanol and micellar liquid chromat…
1999
Abstract A simple and rapid HPLC method for the determination of phenolic antioxidants (propyl and octyl gallates, tert -butylhydroquinone and 3- tert -butyl-4-hydroxyanisole) in sunflower, corn and olive oils, margarine, lard and butter oil is described. The samples are diluted with n -propanol, filtered and injected; solutions containing 30% (w/w) sample can be injected. The analytes are separated with a C18 column and a micellar mobile phase containing 0.1 M SDS, 2.5% n -propanol and 10 mM phosphate of pH 3, and detected at 290 nm. Calibration curves are linear ( r > 0.9999) and the limits of detection range from 0.2 to 1.3 ng, which correspond to antioxidant concentrations well below t…
Bioanalysis of digoxin and its metabolites using direct serum injection combined with liquid chromatography and on-line immunochemical detection.
1994
Abstract An automated dual-column liquid chromatographic assay for digoxin is described. Serum samples are directly injected onto a restricted-access solid-phase extraction support. After liquid chromatographic (LC) separation on a C18 analytical column, antigenic analytes are detected by means of post-column immunochemical detection (ICD) using fluorescein-labelled antibodies against digoxigenin. The detection limit of this assay is 160 pg/ml (preconcentration of 1.0 ml serum). With the present method digoxin and three of its cross-reactive metabolites were determined in serum taken from patients which were orally administered a 1-mg dose of digoxin. The results obtained with LC—ICD were c…
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…
Determination of aluminum at the parts per billion level by solvent extraction and flame atomic emission spectrometry
1991
A new method for the determination of aluminum at the parts per billion level, by N 2 O/ C 2 H 2 flame emission spectrometry with prior solvent extraction with acetylacetone or 8-hydroxyquinoline in 4-methylpentan-2-one, has been performed. The influence of extraction conditions and instrumental parameters on the sensitivity, precision, and dynamic range of the emission calibration curves have been studied. The limit of detection is between 5 and 10 ppb for both ligands, the variation coefficient being 0.2 and 3% at levels of 75 and 25 ppb, respectively. The method has been applied to the determination of Al in water and the results obtained are compared with those found by the standard add…
Study of passive sampling of polycyclic aromatic hydrocarbons in gas phase using Amberlite XAD resins as filling materials of semipermeable membranes
2013
Abstract In this work, a study was performed to evaluate the use of Amberlite XAD resins (XAD-2, XAD-4 and XAD-16), for the first time, as filling materials for low-density polyethylene membranes, which will be inserted as passive samplers for polycyclic aromatic hydrocarbons (PAHs) in gas phase. The use of samplers deployed for 48 h evidenced a relative capability to retain the compounds under study. A detailed study was performed to evaluate the recovery of analytes from the sampler through microwave-assisted extraction by using acetonitrile. A clean-up step using alumina-C18 cartridges was necessary before determination of the PAHs by high performance liquid chromatography with fluoresce…
Fast Separation and Determination of Sterols in Vegetable Oils by Ultraperformance Liquid Chromatography with Atmospheric Pressure Chemical Ionizatio…
2010
A method for the determination of sterols in vegetable oils by ultraperformance liquid chromatography (UPLC) with atmospheric pressure chemical ionization mass spectrometry detection has been developed. The separation of sterols was optimized in terms of mobile phase composition, column temperature and flow rate. The optimal conditions were achieved using an Acquity UPLC BEH C18 column (50 x 2.1 mm, 1.7 microm) with a mobile phase consistent of acetonitrile/water (0.01% acetic acid) using a linear gradient, at a flow rate of 0.8 mL min(-1) and column temperature of 10 degrees C, giving a total analysis time below 5 min. The determination was performed in selective ion recording mode. The li…
Comparison of gas and liquid chromatography coupled to mass spectrometry for the residue analysis of pesticides in organges
2001
Liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI), and gas chromatography-mass spectrometry (GC-MS) with electron impact ionization (EI), are compared for the determination of eight pesticides in oranges. Seven of the selected pesticides, chlorpyriphos, chlorpyriphos-methyl, imazalil, α and β-endosulfan, endosulfan sulphate and dicofol, are commonly determined by GC whereas one, thiabendazole, can only be directly determined by LC. Primary ions [M-H]− or [M-Cl+O]− are obtained using LC-APCI-MS in negative ionization (NI) mode. In contrast, a high degree of fragmentation is reported with GC-MS. Both techniques were applied to oranges, which …
Determination of fungicide residues in fruits and vegetables by liquid chromatography–atmospheric pressure chemical ionization mass spectrometry
2002
Abstract A liquid chromatography (LC) method for the quantitative determination of five fungicide residues (dichloran, flutriafol, o -phenylphenol, prochloraz and tolclofos methyl) in oranges, lemons, bananas, peppers, chards and onions is described. The residues were extracted by matrix solid-phase dispersion (MSPD) using C 8 . Quantitative analysis was performed by isocratic LC coupled to quadrupole mass spectrometer using atmospheric pressure chemical ionization in the negative ionization mode. The limit of quantification was 0.01 mg kg −1 for flutriafol, o -phenylphenol and dichloran, and 0.1 mg kg −1 for prochloraz and tolclofos methyl. The MSPD method is also suitable for LC–UV analys…