Search results for "SEPARATION"

Chemometric extraction of analyte-specific chromatograms in on-line gradient LC-infrared spectrometry

2009

This work exploits the possibilities offered by the recently developed multivariate method named Science-Based Calibration (SBC), for the extraction of ‘analyte-specific’ chromatograms in on-line gradient reversed phase LC-infrared spectrometry (IR) in the presence of a high spectral and chromatographic overlapping between the analyte of interest, co-eluting sample matrix constituents and the mobile phase components. The SBC method uses an experimentally measured single response spectrum of the analyte of interest and representative noise to calculate an optimum regression vector (bopt(1)). Then, the bopt(1) vector is used to predict the concentration of the analyte of interest in the spect…

Bubble fractionation of enantiomers from solution using molecularly imprinted polymers as collectors.

1998

Adsorptive bubble separation methods have been used to enrich components from both heterogeneous and homogeneous solutions. These methods are particularly effective for processing large solution volumes at low cost. Previous work demonstrated that chiral, surface-active collectors could be used to enrich enantiomers from homogeneous solution in a foam fractionation process. In a significant extension of this work, the use of highly selective molecularly imprinted polymers (MIPs) and heterogeneous solutions for the bubble flotation of enantiomers was evaluated. The high selectivity and ease of recycling of the MIP make this a potentially powerful approach for process-scale separations from l…

High-performance liquid chromatographic separation of esters of 4-hydroxymethyl-7-methoxy-coumarin

1978

Finding the best separation in situations of extremely low chromatographic resolution.

2010

Abstract Samples with a large number of compounds or similarities in their structure and polarity may yield insufficient chromatographic resolution. In such cases, however, finding conditions where the largest number of compounds appears sufficiently resolved can be still worthwhile. A strategy is here reported that optimises the resolution level of chromatograms in cases where conventional global criteria, such as the worst resolved peak pair or the product of elementary resolutions, are not able to detect any separation, even when most peaks are baseline resolved. The strategy applies a function based on the number of “well resolved” peaks, which are those that exceed a given threshold of…

Preparation of Pd coated anodic alumina membranes for gas separation media

2007

Different procedures of Pd electroless deposition onto anodic alumina membranes were investigated to form a dense metal layer covering pores. The main difficulty was related to the amorphous nature of anodic alumina membranes, determining low chemical stability in solutions at pH > 9, where Pd plating works more efficiently. As a consequence, it was necessary to find the operative conditions allowing Pd deposition without damaging the membrane: to reduce alumina dissolution, the plating bath was buffered at pH 8.5 by addition of either NaHCO 3 or Na 2 B 4 O 7 ·H 2 O. Acceptable conversion of Pd was found after a deposition time of 3 min. Single and multiple deposition steps (each lasting 3 …

Analytical Techniques for Furosemide Determination

2006

Abstract Due to the clinical importance of furosemide, a large number of analytical procedures to detect the presence of this drug in pharmaceutical and physiological samples has been developed. In this manuscript, a review of the most frequent analytical techniques described to determine furosemide is presented. Special attention has been paid to spectrophotometric and chromatographic techniques, but also to relevant methods using capillary electrophoresis or flow‐injection analysis, as well as the detection modes coupled to these techniques. The review also focuses on the different degradation pathways of the drug and cautions to prevent it, otherwise rarely or confusedly mentioned in the…

Negative pressure cavitation extraction and antioxidant activity of genistein and genistin from the roots of pigeon pea [Cajanus cajan (L.) Millsp.]

2010

Abstract A new method—negative pressure cavitation extraction (NPCE) was proposed and investigated for the extraction of the main isoflavonoids, namely genistein and genistin from pigeon pea roots. The effects of extraction time and particle size on the extraction yields were firstly optimized, then a central composite design (CCD) combined with response surface methodology (RSM) was used to study the effects of negative pressure, ethanol concentration and liquid/solid ratio on the extraction yields. The maximum extraction yields of genistein and genistin reached 0.418 and 0.398 mg/g, respectively, under the optimal conditions: extraction time 45 min, particle size 50 mesh, negative pressur…

Production, isolation and characterization of radiochemically pure 163Ho samples for the ECHo-project

2018

Abstract Several experiments on the study of the electron neutrino mass are based on high-statistics measurements of the energy spectrum following electron capture of the radionuclide 163Ho. They rely on the availability of large, radiochemically pure samples of 163Ho. Here, we describe the production, separation, characterization, and sample production within the Electron Capture in Holmium-163 (ECHo) project. 163Ho has been produced by thermal neutron activation of enriched, prepurified 162Er targets in the high flux reactor of the Institut Laue-Langevin, Grenoble, France, in irradiations lasting up to 54 days. Irradiated targets were chemically processed by means of extraction chromatogr…

Near-critical carbon dioxide extraction and liquid chromatography determination of UV filters in solid cosmetic samples: A green analytical procedure

2005

Near-critical carbon dioxide extraction of four UV filters used as sunscreens in lipsticks and makeup formulations is reported. Extraction parameters were optimized. Efficient recoveries were obtained after 15 min of dynamic extraction with a 80:20 CO2/ethanol mixture at 300 atm and 54 degrees C, using a 1.8 mL/min flow rate. Extracts were collected in ethanol, and appropriately diluted with ethanol and 1% acetic acid to obtain a 70:30 v/v ethanol/1% acetic acid solution. The four UV filters were determined by LC with gradient elution using ethanol/1% acetic acid as mobile phase. The accuracy of the analytical procedure was estimated by comparing the results with those obtained by methods b…

Supported liquid membrane extraction of glyphosate metabolites

2001

Use of the supported liquid membrane (SLM) technique for (aminomethyl)phosphonic acid (AMPA) extraction is presented. For the extraction of this analyte a suitable SLM system involves a liquid membrane containing Aliquat 336 – a cationic carrier that facilitates AMPA transport. The extraction of this compound, as in the case of glyphosate, is dependent on the donor phase pH and the concentration and type of counter-ion in the acceptor phase, although some differences are also observed. In both cases the transport mechanism is counter-coupled transport in which the driving force of mass transport over the membrane is created by the gradient of chloride anions from the acceptor to donor phase.