Biomedical subjects

M Ashraf-Khorassani

Publications and source records attributed to M Ashraf-Khorassani.

11 recordsLinked to original sources

PubMed2005

Isolation of tetra-acyl sucrose esters from turkish tobacco using supercritical fluid CO2 and comparison with conventional solvent extraction.

Pure supercritical CO2 at various pressures and temperatures was used to effect the fractionation of tetra-acyl sucrose esters (SE) from dried, ground Turkish tobacco without any further pretreatment of the matrix. It was determined that SE cannot be extracted using low density CO2 (150 atm, 60 degrees C, and 0.62 gm/mL or 200 atm, 100 degrees C, and 0.49 gm/mL), whereas other analytes, which strongly interfere with the conventional solvent extraction of SE, can be easily removed under the same conditions. At the higher temperature (100 degrees C), these same analytes that interfere with the conventional solvent extraction of SE are even more readily removed, while the very poor extractability of SE is not affected. It was demonstrated, however, that SE can be removed from the pre-extracted tobacco with supercritical CO2 if the density is greater than (or equal to) 0.73 gm/mL. The supercritical fluid extraction method has been compared with other previous extraction methods that employ conventional solvents. This study provides one of the clearest examples of how the variable density property of a supercritical fluid can be utilized to effect the fractionation of a complex mixture.

Carbon Dioxide↗

PubMed2003

Feasibility of supercritical fluid extraction with on-line coupling of reversed-phase liquid chromatography for quantitative analysis of polymer additives.

An on-line analytical method for determining polymer additives which incorporates (a) sample preparation and concentration, (b) chromatographic separation, and (c) UV detection is presented. The on-line system which combines supercritical fluid extraction (SFE) and high-performance liquid chromatography (LC) allows analytes to first be extracted and transferred to the SFE sorbent trap, then desorbed from the trap and presented to the LC system. No UV detector interference from residual dissolved CO2 in the mobile phase was observed since CO2 is eliminated by a pre-wash of the sorbent trap with a small amount of water. Reversed-phase LC with a mobile phase gradient of acetonitrile-water was employed. The described method allows a complete analysis to be processed in less than 30 min.

Chromatography, Liquid↗

PubMed2002

Comparison of gravimetry and hydrolysis/derivatization/gas chromatography-mass spectrometry for quantitative analysis of fat from standard reference infant formula powder using supercritical fluid extraction.

This paper describes a comparative study of the gravimetric versus hydrolysis/derivatization/gas chromatography-mass spectrometry determination of fat in infant formula. Fat was extracted using supercritical carbon dioxide modified with a small amount of ethanol, the extract was weighed, and the total fat was determined gravimetrically. Subsequently, another sample of the supercritical fluid fat extract was hydrolyzed to yield free fatty acids, which were converted to their methyl ester derivatives (FAMEs). Quantification was performed by GC-MS. NIST Standard Reference Material (SRM-1846) was used to validate both fat determination methods. Results showed that the gravimetric average percent fat was 26.86%, whereas the GC-MS method yielded 24.64%. Some peaks were detected in the ion chromatogram from the GC-MS that were identified as nonfatty acids such as aldehydes, which may account for the higher percentage fat measured as weight of extract rather than measured as FAMEs expressed as triglycerides.

Carbon Dioxide↗

PubMed2001

Demonstrative validation study employing a packed column pressurized fluid chromatography method that provides assay, achiral impurities, chiral impurity, and IR identity testing for a drug substance.

Assay development, assay validation, and documentation are reported here for a single packed column pressurized fluid chromatographic/ultraviolet (UV) method that provides: (1) simultaneous detection and quantification for the chiral drug, the chiral impurity and seven achiral impurities; and (2) a Fourier transform infrared (FT-IR) spectrometric identification test result for the Searle drug substance sample, xemilofiban. The separation is achieved in less than 30 min with three columns in tandem and a gradient of CO2-CH3OH. The post-column flow is split between UV (assay) and FT-IR (identification). Precision and accuracy are consistent within figures of merit obtained by liquid chromatographic-ultraviolet assays on analogous drug substances. The reported procedure combines three typical drug substance tests into one test (e.g. chiral impurities, achiral impurities, and infrared identification).

Chromatography, Liquid↗

PubMed2001

High-performance liquid chromatography coupled with chemiluminescence nitrogen detection for the study of ethoxyquin antioxidant and related organic bases.

The Chemiluminescent Nitrogen Detector (CLND) for use with high-performance liquid chromatography (HPLC) allows for the low-level detection of nitrogen-containing compounds with simple quantitation. The nitrogen selective detector's equimolar response (i.e., equal response for nitrogen independent of its chemical environment) allows for any nitrogen-containing compound to be quantitated as long as the number of nitrogens are known. The HPLC-CLND provides a new detection method for analytes that are not available in large quantities or have unknown chemical or physical characteristics such as oxidation products, metabolites, or impurities. Ethoxyquin is a primary antioxidant that is used to preserve many food products and animal feeds. HPLC-CLND is used in the study of the oxidation products of ethoxyquin because limited quantities of these compounds are available and subsequent calibration curves are difficult to maintain. HPLC-CLND as a new method of detection has been evaluated for its equimolarity of response, linear range, limit of detection, and limit of quantitation.

Antioxidants↗

PubMed2000

Analysis of the sulfomycin component of alexomycin in animal feed by enhanced solvent extraction and supercritical fluid chromatography.

Enhanced solvent extraction (ESE) was used to isolate components of alexomycin from different types of animal feed samples. It was demonstrated that ESE was more economical as regards money and, for this particular matrix, twice as fast as supercritical fluid extraction (SFE) even though it was demonstrated that alexomycin can be extracted from feed quantitatively using both ESE and SFE. Supercritical fluid chromatography was used to separate alexomycin from other co-extractives of feed since liquid chromatography was unable to isolate the alexomycin for quantification purposes. Our results also showed that the concentration of alexomycin in an extruded sample was approximately half of the concentration which was originally added to the feed.

Animal Feed↗

PubMed1999

Comparison of methods for quantitative analysis of additives in low-density polyethylene using supercritical fluid and enhanced solvent extraction.

On-line supercritical fluid extraction-supercritical fluid chromatography (SFE-SFC) with cryogenic trapping was used to extract and separate five additives from a low-density polyethylene (LDPE) sample. A glass tube filled with glass wool afforded excellent collection efficiency for the extracted analytes. Additive spiked sand was employed to optimize the various parameters of the on-line SFE-SFC system. Calibration curves from the spiked sand studies for on-line SFE-SFC were obtained with good linearities for quantitation. Results obtained on additives in LDPE from on-line SFE-SFC were comparable to those from off-line SFE-HPLC and off-line enhanced solvent extraction (ESE)-HPLC for all additives except Irganox 1076. However, the precision obtained with on-line SFE-SFC was lower than that from off-line SFE-HPLC and off-line ESE-HPLC due to the small sample size employed in the on-line system. Considerable clean-up of the ESE extract was required prior to chromatographic analysis. On-line SFE-SFC minimized the sample handling and eliminated the use of organic solvent. Despite the lower than expected precision, the on-line SFE-SFC method for quantitation of polymer additives appears to be reliable and robust for application in routine quality control analysis.

Chromatography, High Pressure Liquid↗

PubMed1999

HPLC/atmospheric pressure chemical ionization-mass spectroscopy of eight regulated sulfonamides.

Reversed phase high performance liquid chromatography coupled with on-line atmospheric pressure chemical ionization mass spectrometry, HPLC,APCI-MS, has been applied to a mixture of eight sulfonamides. In full scan mode, extracted ion chromatograms produced minimum detectable quantities (MDQ) of 0.8 ng on column, for six of the eight regulated sulfonamides investigated. Selected ion monitoring yielded a 50 pg MDQ for sulfamerazine, sulfadiazine and sulfamethazine, while, the other compounds presented higher values. Analysis of supercritical fluid extracts of chicken liver containing sulfadimethoxine were found to be easily detected by HPLC/APCI-MS. In extracts of chicken liver spiked with 25 microg/kg(-1) (25 ppb) of sulfadimethoxine this compound could be detected in selected ion mode, while 100 pg/microl(-1) was detectable in either full scan or single ion modes. The analysis method for extracted sulfadimethoxine also demonstrated good linearity and reproducibility in both single ion and scan mode.

Animals↗

PubMed1996

Comparison of supercritical CHF3 and CO2 for extraction of sulfonamides from various food matrices.

Supercritical CHF3 and methanol-modified CHF3 were compared with supercritical CO2 and methanol-modified CO2 for the extraction of sulfonamides from a spiked sand sample. In addition, a fortified nonfat milk powder, fortified egg yolk, and fortified beef liver were studied. The results showed CHF3 has higher solvating power and selectivity for extraction of two of the three sulfonamides than CO2. Extraction efficiencies of sulfamethazine and sulfadimethoxine using pure CHF3 were more than 45% higher from spiked sand samples and over 200% higher from fortified beef liver samples than pure CO2.

Animals↗

PubMed1989

Gradient separation of PTH-amino acids employing supercritical CO2 and modifiers.

Twenty-four PTH-amino acids are rapidly and efficiently separated on a packed cyanopropyl Zorbax column by gradient elution of supercritical CO2 and tetramethylammonium hydroxide-modified methanol. Complete or partial resolution of 22 derivatives is observed with only valine coeluting with norleucine and lysine coeluting with asparagine. A wide variety of stationary phases and modifiers are investigated with supercritical CO2 in attempting to achieve the separation in less than 15 min. Critical to achieving a rapid and efficient separation is the control of modifier flow into the CO2. No modifier is required for elution of neutral PTH-amino acids. The addition of base plays a major role in the elution of acidic and basic PTH-amino acids. Peak tailing is minimized and the elution order of several peaks is altered upon incorporation of reagent into the mobile phase.

Amino Acids↗

PubMedDate not supplied

Comparison of supercritical CHF3 and CO2 and methanol-modified CHF3 and CO2 for extraction of sulfonamides from chicken liver.

Supercritical CHF3 and methanol-modified CHF3 were compared with supercritical CO2 and methanol-modified CO2 for extraction of sulfonamides from fortified chicken liver admixed with Hydromatrix. Results showed that solvating power and selectivity were higher for supercritical and methanol-modified CHF3 than for supercritical and methanol-modified CO2. Visual observation showed that chicken liver extract obtained with methanol-modified CHF3 was cleaner than that obtained with methanol-modified CO2. Fat precipitated in the solvent trap when CO2 was used as the extraction medium. Also, simple off-line collection of fortified chicken liver extract obtained with CO2 in a solid-phase extraction cartridge (packed with either C18 or alumina) followed by phosphate buffer-methanol (50 + 50) rinse yielded an extract that required no further cleanup for analysis.

Animals↗