Search results for "quantitative analysis"

Online Solid-Phase Extraction LC-MS/MS: A Rapid and Valid Method for the Determination of Perfluorinated Compounds at Sub ng·L-1Level in Natural Water

2018

In this research paper, we report a method able to detect perfluorinated compound at pg·L−1 levels in superficial and underground water samples. An online solid phase extraction HPLC-MS/MS method was developed for the analysis of 12 perfluoroalkyl acids (PFASs). The method is based on injection of 5000 µL of water sample in SPE online WAX column followed by chromatography separation and mass spectrometry determination. SPE online elution was performed by water + 0.05% NH4OH and methanol + 0.05% NH4OH, while separation of target compounds was achieved within 10 min by Gemini chromatographic column operating from 1 to 12 pH range and using a mixture of water-methanol + 0.05% NH4OH. Sub ng·L−1…

Supercritical fluid extraction of resveratrol from grape skin of Vitis vinifera and determination by HPLC

2000

Supercritical fluid extraction of resveratrol from grape skin of Vitis vinifera was studied. Extraction variables such pressure, modifier concentration (ethanol), and extraction time were optimised. Final extraction conditions were: 40 degrees C, 150 bar, 7.5% ethanol and extraction time 15 min. Extraction recovery and precision (variation coefficient between 0.2 and 1.0%) were calculated. The resveratrol content in the ethanolic extract was determined by HPLC with UV detection at 306 nm. Acetic acid-methanol-water was used as the mobile phase, and C-18 and C-8 columns were tested, instrumental parameters were optimised, and analytical parameters were calculated (lineal interval 0-75 mg l(-…

Determination of the UV filters worldwide authorised in sunscreens by high-performance liquid chromatography

2001

Simultaneous determination of organic UV filters worldwide authorised in sunscreen formulations was performed by HPLC with UV spectrophotometric detection. The filters determined were: benzophenone-4, benzophenone-3, butyl methoxydibenzoylmethane, octyl dimethyl PABA, octyl methoxycinnamate, homosalate and octyl salicylate. A C18 stationary phase and an isocratic mobile phase of ethanol-water-acetic acid (70:29.5:0.5) containing 65.4 mM of hydroxypropyl-beta-cyclodextrin, were used with a flow-rate of 0.6 ml/min. UV measurements were carried out at 313 nm. The time required for the analysis was 20 min and the limits of detection were between 1.5 and 2.3 mg/l. The procedure proposed provides…

Some observations on the automation by flow injection analysis of the spectrophotometric determination of amino acids and proteins witho-phthalaldehy…

1992

Automation by flow injection analysis with Spectrophotometric detection of the determination of total amino acids and proteins witho-phthalaldehyde is not straightforward. The use of spectrophotometry, instead of spectrofluorimetry, and of N-acetyl-L-cysteine, instead of the conventional mercaptoethanol is advantageous because of the lower variability of absorptivities with respect to fluorescence yields, and the larger stability of the derivatives. Under adequate working conditions and with leucine as reference, the procedure can be used for the evaluation of total amino acids. A similar procedure is proposed for the analysis of proteins in a sample. Limits of detection are ≈ 1 × 10−5M for…

Selective flow-injection biamperometric determination of sulfur-containing amino acids and structurally related compounds

2001

Abstract A simple and selective flow-injection method for the determination of cysteine and methionine is proposed. The method is based on the reaction of the amino acid with chloramine-T and the subsequent reaction of the excess of chloramine-T with an acidic solution of iodide producing a stoichiometric amount of tri-iodide (diminution of the flow-injection analysis (FIA) peak) which is determined biamperometrically using two platinum electrodes polarized at 100 mV. The calibration graph is linear up to 10 μg ml−1 of cysteine and 30 μg ml−1 of methionine; the limit of detection is 0.06 and 0.1 μg ml−1; the repeatability (also as percent of a series of 70 continuous FIA peaks of 5 μg ml−1 …

Flow injection biamperometric determination of chloramine-T in environmental, pharmaceutical and veterinary samples

2000

Abstract A flow injection assembly for the determination of chloramine-T is proposed. The sample (213 μl) is inserted into the carrier, de-ionized water flowing at 4.1 ml min−1. This carrier merges with a mixture of potassium iodide and sulphuric acid, and the resulting solution flows to the flow cell through a reactor 66 cm long. The chloramine-T oxidises the iodide to tri-iodide. The resulting iodide/iodine ratio is biamperometrically tested. The calibration graph is linear up to 65 μg ml−1 chloramine-T; the limit of detection is 0.5 μg ml−1; the relative standard deviation (r.s.d) of the calibration slope is 2.8% for a series of eight independent calibrations. The r.s.d. of a series of 7…

A bioluminescence technique for quantitative and structure-associated imaging of pyruvate

2006

A novel bioluminescence assay has been developed for measuring pyruvate within sections of snap-frozen tissue in a quantitative manner as well as with a spatial resolution on a microscopical level. The assay was verified via HPLC and two independent photometric tests. The novel assay makes it possible to determine pyruvate concentrations in cryosections in the range of 0-5.0 micromol/g tissue (dry weight). Based on the analysis of samples of given pyruvate concentrations, the assay exhibits a recovery with a deviationor =15%. The minimal detectable amount was 0.02 pmol based on a 20 microm thick tissue section with an area of 1 cm(2). Combination of the already established imaging biolumine…

On-line photoreaction and fluorimetric determination of diazepam.

1993

Column-switching techniques for screening of diuretics and probenecid in urine samples

1994

A method based on high-performance liquid chromatography using column-switching is described for the screening of diuretics and probenecid in urine samples. The system uses a 20- x 2.1-mm i.d. precolumn, packed with a Hypersil ODS-C18, 30-microns stationary phase, for the on-line sample cleanup and enrichment. Untreated urine samples are directly injected, and the precolumn is flushed for 1 min with water to eliminate polar matrix components. The retained analytes are then back-flushed by means of a six-port switching valve onto a Hypersil ODS-C18 analytical column (5 microns, 250- x 4-mm i.d.), where they are separated using an acetonitrile/phosphate buffer (pH = 3) gradient elution. Under…

Biopartitioning micellar chromatography: an in vitro technique for predicting human drug absorption.

2001

The main oral drug absorption barriers are fluid cell membranes and generally drugs are absorbed by a passive diffusion mechanism. Biopartitioning micellar chromatography (BMC) is a mode of micellar liquid chromatography that uses micellar mobile phases of Brij35 under adequate experimental conditions and can be useful to mimic the drug partitioning process in biological systems. In this paper the usefulness of BMC for predicting oral drug absorption in humans is demonstrated. A hyperbolic model has been obtained using the retention data of a heterogeneous set of 74 compounds, which shows predictive ability for drugs absorbed by passive diffusion. The model obtained in BMC is compared with …