Search results for "Method"

High-resolution pyrolysis–gas chromatography with a movable reaction zone

1997

Abstract A new device was constructed for pyrolysis–gas chromatography and it was laboratory tested. The device enables the thermal degradation of polymers inside a capillary pre-column and transfer of the reaction zone into a column oven. The pyrolysis procedure described protects the thermally sensitive compounds prior to pyrolysis, prevents the process of irreversible condensation of high-boiling pyrolysis products during the chromatographic process and eliminates extracolumn effects on the peak broadening.

Improvement of analytical methods in post‐market monitoring of food additives and testing of the improved methods (OC/EFSA/DCM/2012/04): Interim repo…

2014

Negative pressure cavitation accelerated processing for extraction of main bioactive flavonoids from Radix Scutellariae

2011

Abstract To enhance the extraction efficiency and reduce the energy consumption, an emerging technology named negative pressure cavitation extraction (NPCE) has been shown to be a feasible option for the extraction of bioactive compounds in agricultural crops and medicinal plants. Meanwhile, it can be applied at the pilot scale as a manufacturing process for edible and medicinal plants. Currently, NPCE was proposed for extraction of baicalin, wogonoside, baicalein and wogonin from Radix Scutellariae on the basis of a central composite design (CCD) and response surface methodology (RSM). With proper optimization (80 mesh of particle size, 40 mL/g of liquid/solid ratio, 75% aqueous ethanol as…

Dynamic reaction cell inductively couple plasma-mass spectrometry optimization for seawater analysis

2018

Abstract A direct method for dynamic reaction cell inductively coupled plasma- mass spectrometry (DRC-ICP-MS) trace mineral elements determination in seawater was optimized by Experimental Statistical Design. Five instrumental parameters, such as radiofrequency, sample, nebulizer and reaction gas flows, rejection parameter q and axial field voltage were studied. A Plackett-Burman design was used for screening the most important parameters and the most significant ones were optimized with a Central composite design. Fifteen elements and different isotopes for some of these were considered through the study. The optimization was achieved by using three different reaction gases (NH3, CH4 and O…

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…

Ultra-high-pressure liquid chromatography tandem mass spectrometry method for the determination of 9 organophosphate flame retardants in water samples

2016

Few methods are available for comprehensive organophosphate flame retardants (PFRs) detection in water and wastewater. Gas chromatography has been employed previously, but this approach is less selective, not amenable for use with deuterated standards and can suffer unfavorable fragmentation. Ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-QqQ-MS/MS) has become the most promising platform, already applied successfully for analysis of selected PFRs in some environmental matrices like water and wastewater. However, the presence of some interferences from the dissolvent, the equipment and the used materials should be taken into account. The procedure involves: The fir…

Determination of critical eluent composition for polyethylenglycols using on-line liquid chromatography-Fourier transform infrared spectrometry.

2008

In this work, it has been extended to methanol:water mobile phases, the use of a background correction method for on-line LC-FTIR measurements named Univariate background correction based on the use of a reference spectra matrix (UBC-RSM) and absorbance ratios. It permits to overcome the problem related to spectral changes occurring during the gradient elution, which in the past limited the on-line coupling of LC and FTIR to isocratic elutions. The combined use of the aforementioned background correction technique in on-line isocratic and gradient LC-FTIR, and partial least squares (PLS) has been applied for the search of the critical conditions for polymers. Polyethylenglycol (PEG) has bee…

Direct determination of Mancozeb by photoacoustic spectrometry

2006

Abstract A solvent free, fast and environmentally friendly photoacoustic-infrared-based methodology (PAS-FTIR) was developed for the determination of Mancozeb in agrochemicals. This methodology was based on the direct measurement of the transmittance spectra of solid samples and a multivariate calibration model to determine the active ingredient concentration. The proposed partial least squares (PLS) model was made using nine standards prepared by mixing different amounts of kaolin and Mancozeb, with concentrations between 5.43 and 88.10% (w/w). A hierarchical cluster analysis was made in order to classify the samples in terms of similarity in the PAS-FTIR spectra. From their spectra differ…

A New Simple Static Method for the Determination of Solubilities of Condensed Compounds in Supercritical Fluids

2002

Abstract A simple static method based on gravimetric measurements has been adopted to measure the solubility of benzenecarboxylic acid, 2-hydroxy-benzenecarboxylic acid, 4-hydroxy-benzenecarboxylic acid and 1,8-dihydroxyanthraquinone along several isotherms in the temperature range 318–357 K and the pressure interval 7–23 MPa. Solubility data have been correlated with the Zieger–Eckert approach, using the Fedor atomic and group contribution method to estimate the solubility parameter and the molar volume of the solutes. A good agreement was obtained between data reported in the literature and those determined using the proposed method which allows one to measure solubility mole fraction as …

Isolation of chlorinated dibenzothiophenes by high-performance thin-layer chromatography

1991

Abstract Chlorinated dibenzothiophenes can cause environmental problems analogous to chlorinated dibenzodioxins and dibenzofurans. In the analysis of chlorinated dibenzodioxins by gas chromatography—mass spectrometry some unknown chlorinated compounds have been found. The chlorinated dibenzothiophenes have the same m/z values as the corresponding dioxins in low-resolution mass spectrometry and they are found in same planar aromatic compound fraction in alumina and carbon column chromatography. Some chlorinated dibenzothiophenes were synthesized to serve as model compounds in analytical work. High-performance thin-layer chromatography (TLC) with different plates and several eluents was tried…