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At least 325 records · Page 18Linked to original sources
PubMed1991

Chromatofocusing profile of purified human alpha-fetoprotein and albumin differs from those of crude samples: effect of protein concentration of the elution of the sample.

Chromatofocusing was utilized to characterize charge microheterogeneity of purified human alpha-fetoprotein (AFP) and human serum albumin (HSA). Crude cord blood samples yielded three isoforms: AFP-IA, IB, and II, with pIs 4.57 (52%), 4.27 (43%), and less than 4.00 (5%), respectively. In contrast, 10 micrograms of purified AFP or 250,000 cpm of 125I-AFP eluted entirely as isoform AFP-II. 125I-AFP focused in the presence of crude cord blood, amniotic fluid, adult male serum, or 25 mg purified HSA resulted in elution profiles similar to those of crude cord blood. Pure AFP focused along with 0.1, 1.0, 5.0, or 10 mg HSA showed a gradual shift from AFP-II to AFP-I. With greater than or equal to 5 mg HSA, isoform I was further resolve into AFP-IA and IB. Similarly, 250,000 cpm of 125I-HSA, which also eluted entirely as isoform II, showed a gradual shift to isoform I when increasing concentrations of unlabeled HSA were added. The resolution of isoform HSA-I in HSA-IA, IB, and IC was again improved with greater than or equal to 5 mg unlabeled HSA. When carrier proteins of varying pI values were chromatofocused along with purified AFP, it was observed that only those proteins with pIs in the range of AFP caused significant alteration in the relative distribution of AFP. We conclude that sample protein concentration and composition must be carefully considered when chromatofocusing is being used for purified samples and when the elution profiles of samples from different origins and varying protein concentrations are being compared.

Chromatography↗
PubMed1975

[Variance of the air sample in air analysis demonstrated on a sample of atmospheric aerosol].

Particulate matter, sampled during 24-h periods from 200 m-3 urban air, was collected on cellulose filters. Each of the four quarters of the filters was analyzed separately by atomic absorption spectroscopy; the concentration of 11 metals was so determined. The residual standard deviation among the quarters of the filter was 10%. In view of this deviation among the results, attributed to the variance of the air sample, it seems rather doubtful that the intercomparison of air sampling instruments, using ambient air as common "standard", will ever give reliable results. It seems likely that air samples, smaller than the 200 m-3 used here, will show an even greater variance, at least with regard to some specific pollutants.

Air Pollution↗
PubMed1992

Viability of Actinobacillus pleuropneumoniae in frozen pig lung samples and comparison of different methods of direct diagnosis in fresh samples.

A comparative study on different methods of diagnosis of Actinobacillus pleuropneumoniae from both fresh and frozen pig lungs is described. A total of 196 lung tissues with pneumonic lesions were examined for culture isolation on chocolate blood agar, as well as for antigen detection by means of the coagglutination test, the immunodiffusion test and the indirect ELISA. These samples were subsequently frozen for 1 yr and then they were recultured. A. pleuropneumoniae was recovered from fresh lung specimens in 30 cases (15.3%) and from frozen samples in only two cases (0.9%). Such a different degree of isolation demonstrates that long freezing had an adverse effect on the viability of this organism in lung samples. A pleuropneumoniae detection was positive in 134 samples (68.4%) by at least one of the immunological techniques examined. The indirect ELISA was the most sensitive and specific test, with antigen detected in 125 lungs (63.8%). In comparison with the coagglutination and immunodiffusion tests, the sensitivities of the indirect ELISA were 95.8 and 93.7%, and the specificities were 67.0 and 63.4%, respectively.

Actinobacillus pleuropneumoniae↗
PubMed1991

Changes in physiological parameters of rat cerebrospinal fluid during chronic sampling: evaluation of two sampling methods.

Although rat cerebrospinal fluid (CSF) is increasingly being used in pharmacological and biochemical research, methodological studies on basic physiological data are lacking. We have determined the albumin content and number of erythrocytes and leukocytes in CSF obtained by two different methods of sampling from cisterna magna-repeated sampling from an implanted cannula and by repeated punctures. In the initial samples the albumin content was 0.08 +/- 0.03 micrograms/microliters. Chronic cannulation of the cisterna magna resulted in a meningeal reaction with increased cell and albumin content: a reaction that could be reduced but not prevented by using a sterile cannula. The number of leukocytes but not erythrocytes was highly correlated to the albumin content. Repeated sampling in the absence of a permanent cannula did not significantly increase albumin content but carried a higher risk for erythrocyte contamination.

Animals↗
PubMed2006

Simplified analysis of organic compounds in headspace and aqueous samples by high-capacity sample enrichment probe.

A sample enrichment probe (SEP) consisting of a thin rod of an inert material and provided at one end with a short sleeve of polydimethylsilicone rubber was used for the high-capacity sample enrichment of analytes from gaseous and aqueous samples for analysis by gas chromatography (GC) and its hyphenated techniques. The silicone rubber was exposed to the analytical sample, after which the end of the rod carrying the silicone rubber was introduced into the injector and the analytes thermally desorbed and analysed by GC. This technique is similar to, but differs from, solid-phase microextraction (SPME) in that a much larger volume of the sorptive phase is employed, the sorptive phase is not introduced into the inlet of the GC via a needle and the injector is opened to the atmosphere for the introduction and removal of the SEP. In the determination of volatile and semi-volatile organic compounds in gaseous and aqueous media, the SEP technique gave results comparable with those obtained by the stir-bar-sorptive extraction (SBSE) and high-capacity sorption probe (HCSP) techniques. Implementation of the SEP technique requires only minor adaptations to the gas chromatograph and does not require any auxiliary thermal desorption and cryotrapping equipment.

Chromatography, Gas↗
PubMed2006

A simple supported liquid hollow fiber membrane microextraction for sample preparation of trihalomethanes in water samples.

A simple and efficient liquid-phase microextraction (LPME) technique using a supported liquid hollow fiber membrane, in conjunction with gas chromatography-electron capture detector has been developed for extraction and determination of trihalomethanes (THMs) in water samples. THMs were extracted from water samples through an organic extracting solvent impregnated in the pores and filled inside the porous hollow fiber membrane. Our simple conditions were conducted at 35 degrees C with no stirring and no salt addition in order to minimize sample preparation steps. Parameters such as types of hollow fiber membranes, extracting solvents and extraction time were studied and optimized. The method exhibited enrichment factors ranged from 28- to 62-fold within 30 min extraction time. The linearity of the method ranged from 0.2 to 100 microg l(-1). The limits of detection were in the low microg l(-1) level, ranging between 0.01 and 0.2 microg l(-1). The recoveries of spiked THMs at 5 microg l(-1) in water were between 98 and 105% with relative standard deviations (RSDs) less than 4%. Furthermore, the method was applied for determination of THMs in drinking water and tap water samples was reported.

Chromatography, Gas↗
PubMed2006

Field amplified sample stacking coupled with chip-based capillary electrophoresis using negative pressure sample injection technique.

A multi-T microchip for integrated field amplified sample stacking (FASS) with CE separation to increase the chip-based capillary electrophoresis (chip-based CE) sensitivity was developed. Volumetrically defined large sample plug was formed in one step within 5s by the negative pressure in headspace of the two sealed sample waste reservoirs produced using a syringe pump equipped with a 3-way valve. Stacking and separation can proceed only by switching the 3-way valve to release the vacuum in headspace of the two sample waste reservoirs. This approach considerably simplified the operations and the equipments for FASS in chip-based CE systems. Migration time precisions of 3.3% and 1.3% RSD for rhodamine123 (Rh123) and fluorescien sodium salt (Flu) in the separation of a mixture of Flu and Rh123 were obtained for nine consecutive determinations with peak height precisions of 4.8% and 3.4% RSD, respectively. Compared with the chip-based CE on the cross microchip, the sensitivity for analysis of FlTC, FITC-labeled valine (Val) and Alanine (Ala) increased 55-, 41- and 43-fold, respectively.

Alanine↗
PubMed2004

New trend in sample preparation: on-line microextraction in packed syringe for liquid and gas chromatography applications. I. Determination of local anaesthetics in human plasma samples using gas chromatography-mass spectrometry.

A new technique for sample preparation on-line with LC and GC-MS assays was developed. Microextraction in a packed syringe (MEPS) is a new miniaturised, solid-phase extraction technique that can be connected on-line to GC or LC without any modifications. In MEPS approximately 1mg of the solid packing material is inserted into a syringe (100-250 microl) as a plug. Sample preparation takes place on the packed bed. The bed can be coated to provide selective and suitable sampling conditions. The new method is very promising. It is very easy to use, fully automated, of low cost and rapid in comparison with previously used methods. This paper presents the development and validation of a method for microextraction in packed syringe MEPS on-line with GC-MS. Local anaesthetics in plasma samples were used as model substances. The method was validated and the standard curves were evaluated by the means of quadratic regression and weighted by inverse of the concentration: 1/x for the calibration range 5-2000 nM. The applied polymer could be used more than 100 times before the syringe was discarded. The extraction recovery was between 60 and 90%. The results showed close correlation coefficients (R>0.99) for all analytes in the calibration range studied. The accuracy of MEPS-GC-MS was between 99 and 115% and the inter-day precision (n=3 days), expressed as the relative standard deviation (R.S.D.%), was 3-10%.

Anesthetics, Local↗
PubMed2005

Development and validation of a liquid chromatography and tandem mass spectrometry method for determination of roscovitine in plasma and urine samples utilizing on-line sample preparation.

Roscovitine, a purine analogue that selectively inhibits cyclin-dependent kinases, has been considered as a potential anti-tumor drug. The determination of roscovitine in plasma and urine was performed using microextraction in packed syringe as on-line sample preparation method with liquid chromatography and tandem mass spectrometry. The sampling sorbent utilized was polystyrene polymer. 2H3-lidocaine was used as internal standard. The limit of detection for roscovitine was as low as 0.5 ng/mL and the lower limit of quantification was 1.0 ng/mL. The accuracy and precision values of quality control samples were between +/-15% and < or =11%, respectively. The calibration curve was obtained within the concentration range 0.5-2000 ng/mL in both plasma and urine. The regression correlation coefficients for plasma and urine samples were > or =0.999 for all runs. The present method is miniaturized and fully automated and can be used for pharmacokinetic and pharmacodynamic studies.

Calibration↗
PubMed2006

Determination of extremely low (236)U/(238)U isotope ratios in environmental samples by sector-field inductively coupled plasma mass spectrometry using high-efficiency sample introduction.

A method by inductively coupled plasma mass spectrometry (ICP-MS) was developed which allows the measurement of (236)U at concentration ranges down to 3 x 10(-14)g g(-1) and extremely low (236)U/(238)U isotope ratios in soil samples of 10(-7). By using the high-efficiency solution introduction system APEX in connection with a sector-field ICP-MS a sensitivity of more than 5,000 counts fg(-1) uranium was achieved. The use of an aerosol desolvating unit reduced the formation rate of uranium hydride ions UH(+)/U(+) down to a level of 10(-6). An abundance sensitivity of 3 x 10(-7) was observed for (236)U/(238)U isotope ratio measurements at mass resolution 4000. The detection limit for (236)U and the lowest detectable (236)U/(238)U isotope ratio were improved by more than two orders of magnitude compared with corresponding values by alpha spectrometry. Determination of uranium in soil samples collected in the vicinity of Chernobyl nuclear power plant (NPP) resulted in that the (236)U/(238)U isotope ratio is a much more sensitive and accurate marker for environmental contamination by spent uranium in comparison to the (235)U/(238)U isotope ratio. The ICP-MS technique allowed for the first time detection of irradiated uranium in soil samples even at distances more than 200 km to the north of Chernobyl NPP (Mogilev region). The concentration of (236)U in the upper 0-10 cm soil layers varied from 2 x 10(-9)g g(-1) within radioactive spots close to the Chernobyl NPP to 3 x 10(-13)g g(-1) on a sampling site located by >200 km from Chernobyl.

Environmental Pollution↗
PubMed1991

Stagewise, group sequential experimental designs for quantal responses. one-sample and two-sample comparisons.

The use of stagewise, group sequential experimental designs with dichotomous responses in toxicity or drug screening programs is discussed. Such designs represent a compromise between the standard, fixed sample size designs and fully sequential designs. Stagewise group sequential designs place specified numbers of animals on test at each stage, up to a maximum number of stages. The greatest increases in sample size efficiency occur with small numbers of stages, particularly when going from one stage to two. Two-stage designs can result in a 15 to 20 percent reduction in average sample size. Five-stage designs can result in a 30 to 40 percent reduction in average sample size, with no appreciable decrease in Type 1 error or power. Examples of the efficiencies that arose in actual screening programs are given. This paper demonstrates that the routine use of stagewise, group sequential designs in standardized screening protocols can result in substantial savings in animal use with virtually no sacrifice of statistical sensitivity.

Animals↗
PubMed1998

On-line sample preparation of paraquat in human serum samples using high-performance liquid chromatography with column switching.

A new ion-pair high-performance liquid chromatographic method with column-switching has been developed for the determination of paraquat in human serum samples. The diluted serum sample was injected onto a precolumn packed with LiChroprep RP-8 (25-40 microm) and polar serum components were washed out by 3% acetonitrile in 0.05 M phosphate buffer (pH 2.0) containing 5 mM sodium octanesulfonate. After valve switching to inject position, concentrated compounds were eluted in the back-flush mode and separated on an Inertsil ODS-2 column with 17% acetonitrile in 0.05 M phosphate buffer (pH 2.0) containing 10 mM sodium octanesulfonate. The total analysis time per sample was about 30 min and mean recovery was 98.5+/-2.8% with a linear range of 0.1-100 microg/ml. This method has been successfully applied to serum samples from incidents by paraquat poisoning.

Acetonitriles↗
PubMed2000

Optimal sample preparation conditions for the determination of uranium in biological samples by kinetic phosphorescence analysis (KPA).

Kinetic phosphorescence analysis (KPA) is a proven technique for rapid, precise, and accurate determination of uranium in aqueous solutions. Uranium analysis of biological samples require dry-ashing in a muffle furnace between 400 and 600 degrees C followed by wet-ashing with concentrated nitric acid and hydrogen peroxide to digest the organic component in the sample that interferes with uranium determination by KPA. The optimal dry-ashing temperature was determined to be 450 degrees C. At dry-ashing temperatures greater than 450 degrees C, uranium loss was attributed to vaporization. High temperatures also caused increased background values that were attributed to uranium leaching from the glass vials. Dry-ashing temperatures less than 450 degrees C result in the samples needing additional wet-ashing steps. The recovery of uranium in urine samples was 99.2+/-4.02% between spiked concentrations of 1.98-1980 ng (0.198-198 microg l(-1)) uranium, whereas the recovery in whole blood was 89.9+/-7.33% between the same spiked concentrations. The limit of quantification in which uranium in urine and blood could be accurately measured above the background was determined to be 0.05 and 0.6 microg l(-1), respectively.

Humans↗
PubMed1997

The reliability of saliva as a sample for the detection of hepatitis A immunoglobulins under various sampling conditions.

BACKGROUND: Saliva is increasingly being investigated as an alternative to serum for diagnostic and epidemiological testing even though antibody levels are substantially lower in buccal cavity fluids. However, there has been little study on whether buccal cavity activity and/or the timing of saliva sampling affects the diagnostic outcome, particularly in seropositive subjects. The absence of influence by these factors may be critical to the use of saliva for pre-vaccination screening for example. OBJECTIVES: The effects of eating, brushing of teeth and circadian rhythm on the measureable salivary immune status of 42 healthy individuals known to be serum and saliva anti-HAV positive were examined. STUDY DESIGN: A total of 141 saliva samples obtained from the 42 healthy subjects, before and after meals, before and after brushing of teeth and at various timepoints throughout the day, were assayed for total anti-HAV using an in-house saliva based enzyme-immunoassay, previously shown to have a 100% correlation in terms of sensitivity and specificity with a serum based assay. RESULTS: The results indicated that total anti-HAV titres varied according to the time of day and that eating had no significant effect on the total anti-HAV titre, but brushing of teeth did. Titres never varied to the extent that a result was falsely negative at any timepoint. CONCLUSION: These results confirm the usefulness of saliva as a diagnostic sample for the detection of hepatitis A antibody, regardless of sampling times, eating or tooth-brushing.

Antibodies, Viral↗
PubMed1991

Direct introduction of large-volume urine samples into an on-line immunoaffinity sample pretreatment-capillary gas chromatography system.

An immunoaffinity precolumn containing immobilized antibodies raised against the synthetic steroid hormone beta-19-nortestosterone, has been used for the automated sample pretreatment of urine samples containing beta-19-nortestosterone or the related steroids norethindrone and norgestrel. The sample pretreatment system was coupled on-line to a capillary GC. The on-line connection between the immunoaffinity precolumn and the capillary GC was realized with an interface that consisted of a 10 mm X 2 mm i.d. reversed-phase pre-column and a diphenyltetramethyldisilazane-deactivated GC retention gap. After preconcentration on the immunoaffinity precolumn the analytes were eluted and reconcentrated on the reversed-phase precolumn. Subsequently, this precolumn was desorbed with 75 microL of ethyl acetate, which was directly introduced into the retention gap by using partially concurrent solvent evaporation. The system allows the automated pretreatment and GC analysis of 5-25-mL urine samples for the ppt-level determination of 19-norsteroids. The general applicability and potential of on-line immunoaffinity-capillary GC systems are discussed.

Chromatography, Affinity↗
PubMed2004

Microdialysis sampling combined with electron spin resonance for superoxide radical detection in microliter samples.

Quantitation of superoxide radical (O2.-) production at the site of radical generation remains challenging. Microdialysis sampling is an advantageous tool for sampling from localized environments. It is difficult to combine electron spin resonance (ESR) spin traps with microdialysis because O2.- adducts with common nitrone spin traps have shorter half-lives than typical microdialysis collection times. Furthermore, typical dialysate samples (5-15 microL) suffer significant sensitivity loss when diluted for detection in a conventional ESR flat cell (200 microL). To overcome these difficulties, a cyclic hydroxylamine, 1-hydroxy-4-phosphonooxy-2,2,6,6-tetramethylpiperidine (PP-H), which produces a stable nitroxide radical (PP.) product upon reaction with O2.- was employed. Capillary cells (1.4 microL effective volume) coupled with a loop-gap resonator were utilized to measure PP. in microliter microdialysis samples (LOD 0.36 pmol). A xanthine/xanthine oxidase (X/XO) model system provided sustained O2.- production. When PP-H was included in the X/XO medium external to the microdialysis probe, a relative recovery of 22.1 +/- 1.1 and 57.2 +/- 5.7% for PP. was achieved at perfusion fluid flow rates of 0.5 and 1.0 microL/min, respectively. The respiratory burst in interferon-gamma and zymosan-stimulated RAW 264.7 macrophages was also investigated.

Electron Spin Resonance Spectroscopy↗
PubMed2004

Infrared atmospheric pressure MALDI ion trap mass spectrometry of frozen samples using a Peltier-cooled sample stage.

Infrared atmospheric pressure matrix-assisted laser desorption/ionization on an ion trap mass spectrometer is used to analyze frozen samples generated using a Peltier-cooled sample stage. This allows for the analysis of samples in water without the addition of matrix, in near-native conditions, and with minimal loss of water due to evaporation. Analysis of frozen samples is extended to study peptides, carbohydrates, and glycolipids.

Amino Acid Sequence↗
PubMed1997

Rotating sample system: an equivalent of a rotating electrode for microliter samples.

Voltammetric experiments in sample droplets of 20 microL volume were carried out with gold ring electrodes microfabricated on Pyrex substrates. The droplet studied was centered and kept in place by a hydrophobic ring deposited on the substrate around the ring electrode, which also ensured that each sample assume a semispherical shape. A small hole in the center of the substrate filled with an agar gel membrane served as a junction. A mild jet of humidified nitrogen gas directed tangentially at the droplet caused it to rotate at a high rate. Cyclic voltammetry and constant-potential electrolysis of potassium ferricyanide were used to characterize this rotating sample system and to calculate diffusion layer thickness. The results clearly demonstrate that rotating of a semispherical microsample placed above a stationary ring electrode with a mild gas jet can be as effective as a rotating electrode system. As a practical example, voltammetric stripping analysis of 20-120 pmol mercuric nitrate samples was performed with a calibration of good linearity (r2 = 0.988) and a time constant for exhaustive electrolysis of approximately 2 min.

Electrochemistry↗