Search results for "SAM"
showing 10 items of 7385 documents
Analysis of basic drugs by liquid chromatography with environmentally friendly mobile phases in pharmaceutical formulations
2017
Abstract Basic drugs are positively charged in the usual working pH (2–8) in reversed-phase liquid chromatography. This gives rise to a strong association with the residual ionized silanols in conventional silica-based stationary phases, which is translated in poor peak shape and high consumption of organic solvent to get appropriate retention times. Micellar mobile phases containing surfactants give rise to modified stationary phases, where silanols are masked, improving the peak shape. However, mobile phases containing the anionic surfactant sodium dodecyl sulfate (SDS) require a small amount of organic solvent to conveniently decrease the retention of cationic analytes. An alternative is…
Stir bar sorptive-dispersive microextraction mediated by magnetic nanoparticles-metal organic framework composite: Determination of N-nitrosamines in…
2019
Abstract A new analytical method based on the recently proposed stir bar sorptive-dispersive microextraction (SBSDME) technique has been developed to determine eight hazardous N-nitrosamines in cosmetic products. As previous step, a simple clean-up is carried out with hexane to remove those highly lipophilic compounds that disturb the SBSDME step. Subsequently, SBSDME is performed by using magnetic nanoparticles–metal organic framework composite, CoFe2O4/MIL-101(Fe), as sorbent to entrap the target analytes, which are later chemically desorbed and measured by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The experimental variables related to the SBSDME procedure were studied to…
Noninvasive sampling of phenylalanine by reverse iontophoresis.
1999
While iontophoresis is typically associated with drug delivery across the skin, the symmetry of the technique permits its application to the essentially noninvasive withdrawal of biologically important analytes from the subcutaneous space to the body's surface. The identification of other substances which can be monitored by this procedure, and to its optimization and development as a more general clinical chemistry tool, is a long-term objective. In this paper, we describe a preliminary in vitro investigation into the feasibility of extracting and analyzing the amino acid, phenylalanine, with the ultimate aim to develop a diagnostic test for phenylketonuria, a potentially fatal metabolic d…
Analytical strategies to determine quinolone residues in food and the environment
2007
23 páginas, 5 figuras, 5 tablas.
Science based calibration for the extraction of 'analyte-specific' HPLC-DAD chromatograms in environmental analysis
2010
Multivariate science based calibration (SBC) has been applied to the resolution of overlapped peaks in liquid chromatography with diode array detection (LC-DAD). Complex river water samples spiked with 11 pharmaceutical substances resulted in poorly resolved chromatograms containing additional peaks from interfering matrix compounds and a change in the background absorbance due to the mobile phase gradient. Applying the present multivariate approach it was possible to resolve all 11 analytes from overlapping peaks, obtaining linear calibration lines (R2 > 0.96). Recovery percentages on spiked samples ranged between 74.6 and 113.5%, which are quite satisfactory taking into account the low co…
More about sampling and estimation of mercaptans in air samples
2013
[EN] Several strategies have been developed for sampling and determination of volatile thiols. The selectivity and sensitivity of the proposed methodologies are achieved by using a specific derivatizing reagent. The different procedures assayed are based on air sampling followed by derivatization of the analytes with OPA and isoleucine in alkaline solution. The derivatization products are separated and determined by liquid chromatography and fluorescence detection. To start, the derivatization conditions and stability of the derivates have been studied in order to establish the storage conditions. In general, the strategies studied consisted on trapping and detivatization the thiol compound…
Curve resolution procedure for isolating the spectra of unknown interferences from the sample spectrum in analyte determinations
1998
The method described is based on the selection of a wavelength in the sample spectrum that is called ‘reference wavelength’, all measured wavelengths are previously assayed in order to select this reference wavelength. Several wavelengths can be used as the reference. The interferent spectrum is calculated as a function of the interferent absorbance at this wavelength, making use of the ratio between the absorbance of the analyte at the selected wavelength and at every measured wavelength. The proposed methodology can estimate the unknown interferent spectrum from the sample and pure analyte spectra. As a quality guarantee of the estimated spectrum, its shape is also estimated in spiked sam…
Comparison of the solid-phase extraction efficiency of a bounded and an included cyclodextrin-silica microporous composite for polycyclic aromatic hy…
2016
Solid-phase extraction is one of the most important techniques for sample purification and concentration. A wide variety of solid phases have been used for sample preparation over time. In this work, the efficiency of a new kind of solid-phase extraction adsorbent, which is a microporous material made from modified cyclodextrin bounded to a silica network, is evaluated through an analytical method which combines solid-phase extraction with high-performance liquid chromatography to determine polycyclic aromatic hydrocarbons in water samples. Several parameters that affected the analytes recovery, such as the amount of solid phase, the nature and volume of the eluent or the sample volume and …
X-ray analysis on the nanogram to microgram scale using porous complexes
2012
X-ray single-crystal diffraction (SCD) analysis has the intrinsic limitation that the target molecules must be obtained as single crystals. Here we report a protocol for SCD analysis that does not require the crystallization of the sample. In our method, tiny crystals of porous complexes are soaked in a solution of the target, such that the complexes can absorb the target molecules. Crystallographic analysis clearly determines the absorbed guest structures along with the host frameworks. Because the SCD analysis is carried out on only one tiny crystal of the complex, the required sample mass is of the nanogram–microgram order. We demonstrate that as little as about 80 nanograms of a sample …
Evaluation of Thin Film Microextraction for trace elemental analysis of liquid samples using LIBS detection
2021
An analytical methodology based in the combination of Thin Film Microextraction with Laser-induced Breakdown Spectroscopy (TFME-LIBS) was investigated, for the first time, for detection of Cu, Cr, Ni and Pb in aqueous solutions. In this methodology, the analytes were extracted in a thin film of adsorbent material deposited on a solid support, which was introduced in the sample to analyse. After extraction, the analytes retained in the adsorbent were analysed by LIBS. In order to obtain adsorbent films useful for the microextraction step, two different experimental procedures for film generation, denoted as Drop Casting Deposition and Mould Deposition, were evaluated. In both cases, graphene…