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At least 577 records · Page 32Linked to original sources
PubMed2000

Solid-phase microextraction: a promising technique for sample preparation in environmental analysis.

Solid-phase microextraction (SPME) is a simple and effective adsorption and desorption technique, which eliminates the need for solvents or complicated apparatus, for concentrating volatile or nonvolatile compounds in liquid samples or headspace. SPME is compatible with analyte separation and detection by gas chromatography and high-performance liquid chromatography, and provides linear results for wide concentrations of analytes. By controlling the polarity and thickness of the coating on the fibre, maintaining consistent sampling time, and adjusting other extraction parameters, an analyst can ensure highly consistent, quantifiable results for low concentration analytes. To date, about 400 articles on SPME have been published in different fields, including environment (water, soil, air), food, natural products, pharmaceuticals, biology, toxicology, forensics and theory. As the scope of SPME grew, new improvements were made with the appearance of new coatings that allowed an increase in the specificity of this extraction technique. The key part of the SPME fibre is of course the fibre coating. At the moment, 27 variations of fibre coating and size are available. Among the newest are a fibre assembly with a dual coating of divinylbenzene and Carboxen suspended in poly(dimethylsiloxane), and a series of 23 gauge fibres intended for specific septumless injection system. The growth of SPME is also reflected in the expanding number of the accessories that make the technology even easier to use Also available is a portable field sampler which is a self-contained unit that stores the SPME fibre after sampling and during the shipment to the laboratory. Several scientific publications show the results obtained in inter-laboratory validation studies in which SPME was applied to determine the presence of different organic compounds at ppt levels, which demonstrates the reliability of this extraction technique for quantitative analysis.

Chromatography, Gas↗
PubMed2006

Selective sample preparation with bioaffinity columns prepared by the sol-gel method.

Bioaffinity materials prepared by entrapping highly selective bioligands in the pores of a sol-gel glass offer unique advantages for the clean-up of complex sample matrices. The inclusion of sol-gel bioaffinity columns frequently allows the efficient elimination of interfering matrix components and enrichment of analytes in a simple step. After introducing the basic principles the paper reviews the methods for the production of protein-doped sol-gel materials and discusses the characteristics of sol-gel affinity columns by comparing their stability, selectivity, binding capacity and reusability. The potential of sample clean-up with sol-gel affinity columns is demonstrated giving applications in environmental, food and clinical analysis.

Chromatography, Affinity↗
PubMed1994

Supercritical fluid extraction as a sample preparation technique for the direct isolation of drugs from plasma prior to analysis.

Supercritical carbon dioxide was used for the direct extraction of drugs from plasma prior to analysis. The supercritical fluid was directly passed through plasma samples spiked with either a neutral (flavone) or an acidic (ketorolac) drug. The addition of an antifoam agent to the plasma prior to extraction was required to avoid restrictor plugging caused by denaturation of the plasma proteins by the supercritical fluid. The effluent from the extraction cell was bubbled through a small volume of methanol or into an empty tube to trap the extracted drug. The effect of extraction pressure and time on absolute recovery were examined. The absolute recovery, selectivity, precision and accuracy of the supercritical fluid extraction approach was compared to conventional liquid-liquid extraction using reversed-phase HPLC with ultraviolet detection.

Animals↗
PubMed2001

High-temperature, microwave-assisted UV digestion: a promising sample preparation technique for trace element analysis.

A novel, microwave-assisted, high-temperature UV digestion procedure was developed for the accelerated decomposition of interfering dissolved organic carbon (DOC) prior to trace element analysis of liquid samples such as, industrial/municipal wastewater, groundwater, and surface water, body fluids, infusions, beverages, and sewage. The technique is based on a closed, pressurized, microwave digestion device. UV irradiation is generated by immersed electrodeless Cd discharge lamps (228 nm) operated by the microwave field in the oven cavity. To enhance excitation efficiency an antenna was fixed on top of the microwave lamp. The established immersion system enables maximum reaction temperatures up to 250-280 degrees C, resulting in a tremendous increase of mineralization efficiency. Compared to open UV digestion devices, decomposition time is reduced by a factor of 5 and the maximum initial concentration of DOC can be raised by at least a factor of 50. The system's performance on a real-type sample was evaluated for the mineralization of skimmed milk (IRMM, CRM 151) and subsequent determination of trace elements using standard spectroscopic techniques. Recovery for Cd (109%), Cu (112%), Fe (99%), and Pb (96%) showed good agreement with the 95% confidence interval of the certified values.

Animals↗
PubMed1990

Improved sample preparation in determination of urinary metanephrines by liquid chromatography with electrochemical detection.

In this relatively simple procedure for extracting metanephrines from urine, after an internal standard (4-hydroxy-3-methoxybenzylamine in 1 mmol/L HCl) is added, the sample is hydrolyzed in a boiling water bath, then treated with ammonia and alumina. Excess ammonia is removed under reduced pressure and the sample is applied to a 1-mL Bond Elut SCX column, which is washed, and metanephrines and internal standard are eluted with 0.5 mmol/L sodium acetate/acetonitrile (3/1 by vol). Of this elute, 5 microL is injected into a 15 cm x 4.6 mm (i.d.) column packed with 5-microns octadecylsilyl silica particles, which is eluted with a mobile phase containing tetramethylammonium perchlorate. Peaks are detected coulometrically at +0.28 V. In the resulting chromatogram, metanephrines give sharp peaks, well resolved from peaks for solvent and internal standard. There are no extraneous peaks for catechols or mono-oxygenated phenylethylamines. Results correlated well (r = 0.999, n = 13) with those by earlier described liquid-chromatography.

Aluminum Oxide↗
PubMed2005

Optimized sample preparation for isotopic analyses of CO2 in air: systematic study of precision and accuracy dependence on driving variables during CO2 purification process.

A systematic analysis of efficiency, reproducibility and accuracy of cryogenic purification of CO(2) from air samples for isotopic analyses is presented. The technical characteristics of the cryogenic line are given in detail. To study the cryogenic process, three different operating parameters are considered: flow rate of the gas entering the line, pressure of the gas in the line, and CO(2)-trap shape. Experimental results demonstrate that efficiency, reproducibility and accuracy strongly depend on the CO(2)trap shape. Moreover, a dependence of reproducibility and accuracy on the flow rate of the gas is found, but not on its pressure. High precision (< or =0.02 per thousand for delta(13)C and < or =0.05 per thousand for delta(18)O) and good accuracy (<0.09 per thousand for delta(13)C and <0.14 per thousand for delta(18)O) is achieved after applying the N(2)O correction.

Journal Article↗
PubMedDate not supplied

Determination of verapamil and norverapamil in human plasma by liquid chromatography: comparison between a liquid-liquid extraction procedure and an automated liquid-solid extraction method for sample preparation.

A conventional liquid-liquid extraction (LLE) procedure with high-performance liquid chromatography (HPLC) has been developed for the determination of verapamil and its main metabolite, norverapamil, in plasma. After addition of the internal standard, plasma samples were basified with phosphate buffer (pH 9.0) and extracted with a mixture of cyclohexane-dichloromethane. After centrifugation, the organic layer was separated and the analytes were extracted back into a 0.1 N sulphuric acid solution containing 2-aminoheptane. An aliquot of this aqueous phase was then injected directly onto the HPLC column. This LLE procedure has been compared with an automated liquid-solid extraction (LSE) method that has been developed in parallel. Good linearity was obtained using both extraction methods. The absolute recoveries for the two analytes were ca 95% with the automated LSE procedure and slightly lower (ca 84%) for the LLE method. The automated method gives better results with respect to detectability and precision, but the LLE procedure is simpler to develop, requires much less expensive equipment, and remains a useful alternative when the number of samples to be analysed is limited.

Buffers↗
PubMed2002

On-line automated sample preparation for liquid chromatography using parallel supported liquid membrane extraction and microporous membrane liquid-liquid extraction.

An automated system was developed for analysis of non-polar and polar ionisable compounds at trace levels in natural water. Sample work-up was performed in a flow system using two parallel membrane extraction units. This system was connected on-line to a reversed-phase HPLC system for final determination. One of the membrane units was used for supported liquid membrane (SLM) extraction, which is suitable for ionisable or permanently charged compounds. The other unit was used for microporous membrane liquid-liquid extraction (MMLLE) suitable for uncharged compounds. The fungicide thiophanate methyl and its polar metabolites carbendazim and 2-aminobenzimidazole were used as model compounds. The whole system was controlled by means of four syringe pumps. While extracting one part of the sample using the SLM technique. the extract from the MMLLE extraction was analysed and vice versa. This gave a total analysis time of 63 min for each sample resulting in a sample throughput of 22 samples per 24 h.

Automation↗
PubMed1978

Comparison of sample preparation procedures for colorimetric analysis of nitrite in frankfurters.

Three groups of methods for analyzing nitrite in meat are compared. All methods consist of a sequence of steps, grouped according to initial extraction procedures. In Group 1, the sample is treated with borate followed by HgCl2 or Carrez I, and then Carrez II. In Group 2, the sample is diluted with water, heated at 80 degrees C, and analyzed immediately (AOAC) or after addition of either Na2CO3 and FeCl3 or HgCl2. In Group 3, the sample is made alkaline with NH4Cl buffer and then treated with one of the following: activated carbon plus Carrez I and II, alumina cream, or AIK(SO4)2. At each step when the method involved the addition of a chemical, supernates and precipitates (if formed) were analyzed for nitrite by Griess reagent both before and after AOAC digestion. The normally discarded precipitates formed after addition of HgCl2 and Carrez I and II contained bound nitrite that could be detected by AOAC analysis. Except in the AOAC method, HgCl2 improved nitrite analysis. Results by AOAC analysis were 3 to 300% higher than those determined after addition of any chemical or combination of chemicals. Spiked meat samples could not be used in comparing nitrite analysis methods because results were misleading. Acid meat samples, such as fermented sausages, required neutralization before AOAC analysis.

Animals↗
PubMed1996

Improved sample preparation for cross-sectional transmission electron microscopy of layered structures using rocking-angle ion-milling techniques.

The rocking-angle ion-milling technique has been employed to produce optimum Pt/Ti/SiO2/Si, W/TiN/SiO2/Si, and (Pb,La)TiO3/Pt/MgO samples for cross-sectional transmission electron microscopy (TEM). Because of the different ion-milling rates between film layers and substrate materials, no satisfactory cross-sectional TEM samples could be obtained when they were made by the conventional ion-milling method. The differential thinning problems could be effectively solved by optimizing both ion-milling rocking-angle and ion-beam incidence angle without the increase of overall milling time. It was found that the rocking-angle of around 40 degrees is good when the multilayer structure is composed of materials with great ion-milling rate differences, while the rocking angle of around 80 degrees is good when the ion-milling rate differences are relatively small.

Microscopy, Electron↗
PubMed2005

Sample preparation followed by high performance liquid chromatographic (HPLC) analysis for monitoring muconic acid as a biomarker of occupational exposure to benzene.

Factors affecting solid phase extraction (SPE) of trans,trans-muconic acid (ttMA), as a benzene biomarker, including sample pH, sample concentration, sample volume, sample flow rate, washing solvent, elution solvent, and type of sorbent were evaluated. Extracted samples were determined by HPLC-UV (high performance liquid chromatography-ultraviolet). The analytical column was C18, UV wave length was 259 nm, and the mobile phase was H(2)O/methanol/acetic acid run at flow rate of 1 ml/min. A strong anion exchange silica cartridge was found successful in simplifying SPE. There was a significant difference between recoveries of ttMA when different factors were used (p < .001). An optimum recovery was obtained when sample pH was adjusted at 7. There was no significant difference when different sample concentrations were used (p > .05). The optimized method was then validated with 3 different pools of samples showing good reproducibility over 6 consecutive days and 6 within-day experiments.

Air Pollutants, Occupational↗
PubMed2005

Direct integration of pervaporation as a sample preparation method for a dedicated "electronic nose".

The present study investigates the possibility of monitoring the bioproduction of a complex aroma profile with an analytical electronic aroma-sensing technique, the so-called "electronic nose", combined with a pervaporative sample enrichment method necessary to overcome the ethanol interference on the sensors' response. It presents in detail the development of a direct integrated pervaporation-electronic nose unit for a simple and fast analysis, which are key criteria for this technique to be broadly implemented. The system developed was investigated using model solutions simulating the muscatel wine must fermentation. It proved to be able to evaluate different relevant aroma compounds in solutions of varying degree of complexity, and also in the presence of ethanol, which is a major interference on the sensors' response to the aromas. The transient sensors' response was investigated in detail, revealing information for sample discrimination and reducing the analysis time. The system developed allowed a simple, fast, and selective analysis, therefore permitting a high sample throughput over time, with the possibility of fully automation.

Electrons↗
PubMed2002

Optimum methamphetamine profiling with sample preparation by solid-phase microextraction.

Solid-phase microextraction (SPME) is a relatively new technique in which a small, polymer-coated fiber is employed to extract volatile and semivolatile organic compounds from the sealed headspace above a questioned sample. SPME, coupled with gas chromatography/mass spectrometry (GC/MS), was used to characterize impurities in illicit methamphetamine samples. Trace impurities present in a specimen were tentatively identified using mass-spectral databases and included 1,2-dimethyl-3-phenyl-aziridine (indicating synthesis via a halogenated ephedrine intermediate), ethyl vanillin (a flavoring compound), and caffeine (a stimulant used as cutting agent). The types and numbers of organic compounds sampled by SPME were compared with those collected by various solvent extraction protocols. In addition to unambiguously confirming the presence of methamphetamine, SPME-GC/MS analyses detected approximately 30 more organic analytes than were found by GC/MS following the ethyl acetate extraction method adopted by the United Nations International Drug Control Programme. SPME-GC/MS is a superior method for generating material "fingerprint" profiles in methamphetamine samples. The detection and characterization of increased points of comparison in drug samples provide more detailed chemical signatures for both intelligence and operational information.

Journal Article↗
PubMed1999

Development of a simple sample preparation technique for gas chromatographic-mass spectrometric determination of nicotine in edible nightshades (Solanaceae).

The purpose of this study was to develop a rapid analytical method for the reliable determination of low concentrations of nicotine in foods for large numbers of samples. Food material was extracted using a simple liquid-liquid extraction method. For processed foods, further clean-up steps had to be employed to eliminate interfering compounds. The determination of nicotine was performed by gas chromatography-mass spectrometry. Quantitative analysis was accomplished using deuterium labeled nicotine as an internal standard. Recoveries of over 95% were obtained for a single step extraction, as well as for a multiple-stage extraction procedure, respectively. The method has been applied to the determination of nicotine in edible nightshades (i.e. tomatoes, potatoes and aubergines) and their processed products.

Air↗
PubMed1997

Influence of sample preparation on analytical results: drug analysis [GC/MS] on hair snippets versus hair powder using various extraction methods.

The comparison of aqueous extraction methods and hair extraction by organic solvents performed on hair powder as well as on hair snippets of the same sample revealed different qualities of the procedures. Qualitative and quantitative results by the same derivatization step and GC/MS detection demonstrated, that the risk of missing a drug substance is higher using hair snippets than after drug extraction on pulverised hair. Drug recovery for opiates, cocaine and benzoylecgonine from hair was found to be best in aqueous solvents or in methanol extracts. The results are discussed under the aspects of solid-phase extraction, the hair sample representing an inhomogenous material. The localisation of drug molecules in hair, the hair swelling and penetration behavior of the particular extraction medium as well as the partition coefficient of solvent/hair phase for a particular drug substance are considered to influence the results.

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Microfluidic devices for DNA sequencing: sample preparation and electrophoretic analysis.

Modern DNA sequencing 'factories' have revolutionized biology by completing the human genome sequence, but in the race to completion we are left with inefficient, cumbersome, and costly macroscale processes and supporting facilities. During the same period, microfabricated DNA sequencing, sample processing and analysis devices have advanced rapidly toward the goal of a 'sequencing lab-on-a-chip'. Integrated microfluidic processing dramatically reduces analysis time and reagent consumption, and eliminates costly and unreliable macroscale robotics and laboratory apparatus. A microfabricated device for high-throughput DNA sequencing that couples clone isolation, template amplification, Sanger extension, purification, and electrophoretic analysis in a single microfluidic circuit is now attainable.

Base Sequence↗
PubMed2000

A comparative study on methods of optimal sample preparation for the analysis of oligonucleotides by matrix-assisted laser desorption/ionization mass spectrometry.

Metal adducts (e.g., Na+ and K+) significantly hinder the analysis of oligonucleotides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Although a number of sample purification methods exist, to date no comparative study exists to determine the most efficient method for purifying oligonucleotides. The objective of this work was to perform such a study. Several different oligonucleotide samples were synthesized. Aliquots of these samples were then purposely contaminated with sodium acetate to generate representative contaminated (salted) oligonucleotide samples. A number of popular oligonucleotide purification techniques were then tested as to their effectiveness at removing Na+ from the salted samples. The effectiveness of Na+ removal was qualitatively assessed by comparing the MALDI mass spectra of the original sample, the salted sample, and the salted sample after purification. Micropipet tips packed with C18 reversed-phase packing material (e.g., Zip Tips) appear to be the most effective means of purifying the oligonucleotides investigated. Minidialysis was found to be an effective alternative for purifying higher molecular weight oligonucleotides (> 10,000 u).

Chemistry Techniques, Analytical↗
PubMed1995

Sample preparation, high-performance liquid chromatographic separation and determination of substance P-related peptides.

This review deals with the determination of low levels of substance P and peptide fragments derived from the undecapeptide, i.e. covers the whole amount of so-called substance P-like immunoreactivity (SPLI) in biological samples. First an overview of the most currently used sample pretreatment procedures is given, followed by a description of the most effective high-performance liquid chromatographic (HPLC) separation methods. Special attention is paid to the choice of the appropriate column and the possible pitfalls encountered in separation of fmol amounts of peptide material. Subsequently the most important techniques of detection are discussed. This section primarily focuses on the coupling of HPLC with radioimmunoassay (RIA), which is indispensable for detection of components in the fmol range at present. Finally, some aspects of preparation and chromatographic separation of radiolabelled antigens for use in RIA are discussed.

Amino Acid Sequence↗