Search results for " Phase"
showing 10 items of 1862 documents
Sensitive determination of ethacrynic acid in urine samples by reversed-phase liquid chromatography with ultraviolet detection using solid-phase extr…
1992
Abstract A rapid method is described for the identification and determination of ethacrynic acid in human urine samples by liquid chromatography with UV detection, the retention time of the analyte being 4.9 min. The samples were previously conditioned using C 18 solid-phase extraction columns and chromatographed on an HP-LiChrospher RP C 18 column (5 μm; 125 mm × 4 mm i.d.) with gradient elution with acetonitrile-acetate buffer (pH 4). The detector was set at 275 nm and furosemide was used as an internal standard. The procedure was applied to the determination of ethacrynic acid at concentrations of 0.01-10 μg ml -1 and the limit of detection was 6 ng ml -1 .
A solid-phase extraction liquid chromatography-tandem mass spectrometry method for the percutaneous absorption assessment of 3-(4′-methylbenzylidene)…
2013
The UV filter 3-(4′-methylbenzylidene)camphor (MBC) is a common ingredient in sunscreen cosmetic products. However, different in vitro and in vivo studies suggest that MBC can cause endocrine disrupting effects. This report focuses on the development of an analytical method based on solid-phase extraction (SPE) prior to liquid chromatography tandem mass spectrometry (LC-MS/MS) for the determination of MBC and its main phase I metabolite, named 3-(4′-carboxybenzylidene)camphor (CBC), in urine from users of sunscreen cosmetic products containing MBC. The formation of phase II metabolites (i.e., glucuronide and sulphate conjugates) was also considered by carrying out an enzymatic hydrolysis of…
Determination of UV filters in both soluble and particulate fractions of seawaters by dispersive liquid–liquid microextraction followed by gas chroma…
2014
An analytical method to determine the total content (i.e., not only in the soluble fraction but also in the particulate one) of eight commonly used UV filters in seawater samples is presented for the first time. Dispersive liquid-liquid microextraction (DLLME) is used as microextraction technique to pre-concentrate the target analytes before their determination by gas chromatography-mass spectrometry (GC-MS). In order to release the UV filters from the suspended particles an ultrasound treatment is performed before DLLME. The ultrasound treatment time was studied in order to achieve a quantitative lixiviation of the target analytes. The type and volume of both disperser and extraction solve…
Advantages of monolithic over particulate columns for multiresidue analysis of organic pollutants by in-tube solid-phase microextraction coupled to c…
2011
Abstract The performance of a monolithic C 18 column (150 mm × 0.2 mm i.d.) for multiresidue organic pollutants analysis by in-tube solid-phase microextraction (IT-SPME)-capillary liquid chromatography has been studied, and the results have been compared with those obtained using a particulate C 18 column (150 mm × 0.5 mm i.d., 5 μm). Chromatographic separation has been carried out under isocratic elution conditions, and for detection and identification of the analytes a UV-diode array detector has been employed. Several compounds of different chemical structure and hydrophobicity have been used as model compounds: simazine, atrazine and terbutylazine (triazines), chlorfenvinphos and chlorp…
Improving analysis of apolar organic compounds by the use of a capillary titania-based column: Application to the direct determination of faecal ster…
2010
This article reports a new procedure for the direct determination of faecal sterols coprostanol and cholesterol in wastewater samples as tracers of human sewage contamination. The method combines in-tube solid-phase microextraction (IT-SPME) for analyte enrichment and capillary liquid chromatography (LC) for separation with diode array detection for identification and quantification. A titania-based polymeric capillary column and a conventional octadecyl silica (ODS) capillary column were evaluated and compared for their ability to separate the analytes. The titania-based column allowed the separation of the analytes in much shorter chromatographic times and with better chromatographic prof…
Development of a fully automated sequential injection solid-phase extraction procedure coupled to liquid chromatography to determine free 2-hydroxy-4…
2010
Abstract 2-Hydroxy-4-methoxybenzophenone and 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid, commonly known as benzophenone-3 (BZ3) and benzophenone-4 (BZ4), respectively, are substances widely used as UV filters in cosmetic products in order to absorb UV radiation and protect human skin from direct exposure to the deleterious wavelengths of sunlight. As with other UV filters, there is evidence of their percutaneous absorption. This work describes an analytical method developed to determine trace levels of free BZ3 and BZ4 in human urine. The methodology is based on a solid-phase extraction (SPE) procedure for clean-up and pre-concentration, followed by the monitoring of the UV filters by…
Spectrophotometric determination of phenols in water samples by the GHPSAM method
2001
Abstract The generalized H-point standard-additions method (GHPSAM) is proposed in order to obtain the phenol concentration in water samples when the matrix is completely unknown. The procedure involves solid-phase extraction in BondElut PPL cartridges and data handling of the UV-visible spectrophotometry measurements. The spectral regions where the unknown interferent behaviour can be considered as linear are found and the analyte concentration free from bias error is estimated. The percentages of recovery of phenols in spiked samples were similar to those obtained by HPLC. Cresols or chlorophenols can be also determined in real samples by this method. The concentration range tested was 0.…
Exploring hand-portable nano-liquid chromatography for in place water analysis: Determination of trimethylxanthines as a use case.
2020
Abstract Analytical performance and optimization of figures of merit of a portable nano liquid chromatograph (NanoLC) with UV detection at 255 nm have been established for in place analysis. Methylxanthines: caffeine, theophylline and theobromine were selected as target analytes. A fast lab method based on IT-SPME coupled on line with capillary liquid chromatograph (CapLC) with diode array detection (DAD) was employed for comparative studies. IT-SPME and solid phase extraction were coupled off-line to NanoLC for improving instrumental parameters, mainly detection capacity and selectivity. IT-SPME or SPE/portable NanoLC based methods were superior in terms of chromatographic resolution and o…
Stir bar sorptive-dispersive microextraction mediated by magnetic nanoparticles-nylon 6 composite for the extraction of hydrophilic organic compounds…
2016
A new and sensitive analytical method based on the recently developed approach termed stir bar-sorptive dispersive microextraction (SBSDME) using a magnetic CoFe2O4@SiO2-nylon 6 composite as sorbent material is presented for the extraction of hydrophilic organic compounds. The simultaneous determination of four hydrophilic UV filters in environmental water samples has been chosen as a model analytical application due to the increasing awareness regarding the occurrence of sunscreen residuals in natural waters. The developed SBSDME approach combines the principles and benefits of stir bar sorptive extraction (SBSE) and dispersive solid phase extraction (DSPE) but allows for lower extraction …
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…