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Results for “Repeatability and Reproducibility”

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At least 595 records · Page 33Linked to original sources

PubMed2004

Procedure for quantification of platelet adhesion to biomaterials by radioscintigraphy.

Detection of adhered platelets on biomaterial surface that has blood-contacting application is an important test to assess its thrombogenicity. Usually, for measurement of platelet adhesion, after exposure to platelet-rich plasma (PRP) under standardized conditions the test surface is rinsed to remove non-adherent cells and is analyzed under scanning electron microscopy (SEM) to detect morphology of adhered cell and degree of aggregate formation. However, being a qualitative test it is unlikely to give an accurate estimate of platelets adhered to the surface. On the other hand, use of radiolabels enables quantification of platelets deposited on a material or device. Because of high gamma emission of (111)In, it can be used for radioscintigraphy, however, its short half life (2.5 days) is a major hurdle in using it for quantification of platelet adhesion. (125)I is a relatively strong radiolabel that is easily tagged to most of the proteins and has a relatively long half-life (60 days). The major objectives of this study are to standardize the labeling conditions to get good (125)I activity on platelets, while maintaining normal cell function after they are labeled. Considering all possible uncertainties, quantity of isotope and platelets to be used and the conditions of iodination reaction are established to get repeatable and reproducible labeling of platelets. Further, it is demonstrated that (125)I-platelets can be used to determine total number of cells adhered to titanium surface, which is known to be used as a blood-contacting biomaterial.

Biocompatible Materials↗

PubMed2004

The influence of reduced oxygen availability on pathogenicity and gene expression in Mycobacterium tuberculosis.

We investigated how Mycobacterium tuberculosis responded to a reduced oxygen tension in terms of its pathogenicity and gene expression by growing cells under either aerobic or low-oxygen conditions in chemostat culture. The chemostat enabled us to control and vary the oxygen tension independently of other environmental parameters, so that true cause-and-effect relationships of reduced oxygen availability could be established. Cells grown under low oxygen were more pathogenic for guinea pigs than those grown aerobically. The effect of reduced oxygen on global gene expression was determined using DNA microarray. Spearman rank correlation confirmed that microarray expression profiles were highly reproducible between repeat cultures. Using microarray analysis we have identified genes that respond to a low-oxygen environment without the influence of other parameters such as nutrient depletion. Some of these genes appear to be involved in the biosynthesis of cell wall precursors and their induction may have contributed to increased infectivity in the guinea pig. This study has shown that a combination of chemostat culture and microarray presents a biologically robust and statistically reliable experimental approach for studying the effect of relevant and specific environmental stimuli on mycobacterial virulence and gene expression.

Anaerobiosis↗

PubMed2005

3-D measurement of body tissues based on ultrasound images with 3-D spatial information.

In this study, we developed a new method to perform 3-D measurements between the recorded B-scans using the corresponding spatial location and orientation of each B-scan, without the need to create a 3-D volume. A portable ultrasound (US) scanner and an electromagnetic spatial locator attached to the US probe were used. During data collection, the US probe was moved over the region-of-interest. A small number of B-scans containing interesting anatomical information were captured from different body parts and displayed in a 3-D space with their corresponding locations recorded by the spatial locator. In the B-scan planes, the distance between any two points, as well as the angle between any two lines, could be calculated. In validation experiments, three distances and three angles of a custom-designed phantom were measured using this method. In comparison with the results measured by a micrometer, the mean error of distance measurement was -0.8 +/- 1.7 mm (-2.3 +/- 3.6%) and that of angle measurement was -0.3 +/- 2.9 degrees (-0.1 +/- 4.1%). The lengths of the first metatarsals and the angles between the first metatarsals and the middle part of the tibias of three subjects were measured in vivo using magnetic resonance imaging (MRI) and the US method by two operators before and after MRI scanning. The overall percentage differences of the length and angle measurements were 0.8 +/- 2.2% and 2.5 +/- 3.6%, respectively. The results showed that this US method had good repeatability and reproducibility (interclass correlation coefficient values > 0.75). We expect that this new method could potentially provide a quick and effective approach for the 3-D measurement of soft tissues and bones in the musculoskeletal system.

Calibration↗

PubMed2006

A non-invasive QPCR method monitoring DNA based therapy of bladder cancer patients.

Real-time PCR technology is highly advantageous for gene studies based on the genetic nature of the transferred material. Urine and blood samples were collected before and after treatment. Treatment of bladder carcinoma patients with plasmid constructs expressing the diphtheria toxin gene was monitored. Detection range from 5x10(6) copies to <or=10 copies was observed with repeatability and reproducibility. No trace amount of the plasmid was detected in the patient's bloodstream, and a continuous clearance in urine, as well, was observed 72 h post-injection. These results show the possibility to design a follow-up method to monitor quantitatively the amount of the plasmid DNA in bladder cancer patients.

DNA↗

PubMed2007

European Pharmacopoeia foot-and-mouth disease vaccine potency testing in cattle: between test variability and its consequences.

In the event of a foot-and-mouth (FMD) outbreak in a densely populated livestock area within the European Community, emergency vaccination will most likely be employed. The objective of the present study was to support the European FMD control policy by evaluating the between test variability of the European accepted method for assessing the potency, a major determinant in vaccine choice, of an FMD vaccine batch. The test system suffers from low in vivo repeatability and reproducibility (67.6 and 58.8%, respectively). Consequently, the results of 10 identical, individual vaccine potency tests using an FMD virus O1 Manisa vaccine batch indicate that the obtained potency of a vaccine with an overall 50% protective dose (PD(50)) value of 9.99 may vary from 4.59 to 24.25 PD(50).

Animals↗

PubMed2000

Separation and determination of alditols and sugars by high-pH anion-exchange chromatography with pulsed amperometric detection.

Carbohydrates such as alditols (polyols or sugar alcohols), monosaccharides and disaccharides are separated as anions by anion-exchange chromatography with a sodium hydroxide eluent, MA1 CarboPac column and pulsed amperometric detection. We report a high-pH anion-exchange chromatographic-pulsed amperometric detection (HPAEC-PAD) method that determines all the polyols used as food additives in food products and the most commonly found mono- and disaccharides on a routine basis. The linearity, repeatability, internal reproducibility and accuracy are described. The applicability of the method has been demonstrated by the analysis of 46 relevant samples and by participation twice in the Food Analysis Performance Assessment Scheme (FAPAS) testing programme for food additives.

Anion Exchange Resins↗

PubMed2000

Determination of nonylphenol ethoxylate oligomers by liquid chromatography-electrospray mass spectrometry in river water and non-ionic surfactants.

Liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) for the quantitative determination of five nonylphenol ethoxylate (NPE) oligomers in river water was described. These NPE oligomers were separated on a poly(vinyl alcohol) gel column using acetonitrile-30 mM ammonium acetate as the mobile phase followed by ESI-MS detection without any sample concentration steps. The sample was only filtered using the disposable filter and the aliquot (100 micro1) of this sample was injected into the LC-ESI-MS system. All NPE oligomers were detected using the [M+NH4]-ion. Detection limits ranged from 160 pg/ml (NPE4) to 240 pg/ml (NPE2), repeatability and reproducibility ranged from 4.2% (NPE2) to 6.2% (NPE6) and from 7.4% (NPE5) to 9.8% (NPE6).

Chromatography, Gel↗

PubMed2001

Comparison of different fibers for the solid-phase microextraction of phthalate esters from water.

Solid-phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) has been applied to determine six phthalate esters and one adipate ester in water. The SPME parameters were optimized for several commercially available fibers. A 65-microm polydimethylsiloxane-divinylbenzene (PDMS-DVB) was the fiber selected and was applied to analysis of water from the Ebro river and the industrial port of Tarragona. The studied compounds were found at concentrations ranging from 0.4 microg l(-1) for di-n-butyl phthalate ester (DnBP) to 3.2 microg l(-1) for bis(2-ethylhexyl) phthalate ester (DEHP). The linear range for real samples was from 0.1 to 10 microg l(-1) for most phthalates, and the limits of detection of the method were between 3 and 30 ng l(-1). Repeatability and reproducibility between days (n = 5) for 1 microg l(-1) samples were below 13 and 18%, respectively.

Dibutyl Phthalate↗

PubMed2001

Determination of polycyclic aromatic hydrocarbons by liquid chromatography-electrospray ionization mass spectrometry using silver nitrate as a post-column reagent.

Liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) using silver nitrate as a post-column reagent has been used for the determination of 10 polycyclic aromatic hydrocarbons (PAHs) in river water. In this method, after all the PAHs were separated by reversed-phase liquid chromatography, analytes formed complexes with silver cation by mixing with silver nitrate solution. The complexes then transfer the molecular ion, [M]+, of the PAHs by charge transfer using in source collision-induced dissociation. The positive ion ESI mass spectra of all PAHs tested in this study showed [M]+ as the base peak and abundant [M+Ag]+, [2M+Ag]- with very weak or no [2M+Ag]+. For the sample extraction, several solid-phase extraction parameters using the blue-chitin column were optimized. The limits of detection (S/N=3) of all PAHs for the spiked river water sample ranged from 0.001 to 0.03 ng/ml, and the detector responses were linear up to I ng/ml (correlation coefficients > or =0.0998). Repeatability and reproducibility were in the range from 4.3 to 6.8% and from 6.2 to 9.5%, respectively.

Chromatography, Liquid↗

PubMed1984

Capillary fused-silica on-column injection of chlorinated pesticides with an ultra-low volume rotary valve.

Quantitative on-column injections into a fused-silica capillary column were carried out by using a ten-port ultra-low volume rotary switching valve to determine the utility and reproducibility of this rotary valve as an on-column injector. Good reproducibility for repeated injections of chlorinated pesticides was obtained by using an external sample loop and wash loop with the rotary valve. The problems commonly associated with a fine fused-silica or stainless-steel needle on-column capillary injection technique were minimized. The valve was used in the manual mode but can be completely automated with commercially available equipment.

Chromatography, Gas↗

PubMed2003

Stir bar sorptive extraction and large volume injection gas chromatography to determine a group of endocrine disrupters in water samples.

Stir bar sorptive extraction (SBSE) combined with gas chromatography (GC) with mass spectrometric detection (MS) has been applied to determine a group of suspected endocrine disrupters in water samples. One centimeter stir bars coated with PDMS were used to extract the analytes and then solvent desorption was carried out. The absorption and desorption parameters in SBSE were optimized and large volume injection was used with a programmed temperature vaporizer injector (PTV) in GC to enhance the sensitivity of the method. The linear range of some endocrine disrupters was between 0.05 and 5 microg l(-1) and limits of detection were 0.01-0.24 microg l(-1) under full scan acquisition mode. The repeatability and reproducibility of the method (n = 5) for Ebro river water samples spiked at a level of 0.5 microg l(-1) was below 13 and 23%, respectively. Recoveries between 42 and 96% were obtained with the exception of atrazine. The method was applied to analyze real water samples from the Ebro River and irrigation streams of Ebro Delta and some of the compounds studied (aldrin, dieldrin, 4,4'-DDE and 4,4'-DDT) were found in some of them between detection and quantification limits.

Chromatography, Gas↗

PubMed2003

Characterisation of reversed-phase liquid chromatographic columns by chromatographic tests. Rational column classification by a minimal number of column test parameters.

The European Pharmacopoeia (Ph. Eur.) and other official compendia give only a general description of the stationary phase in the description of a liquid chromatographic method. Therefore the selection of a column giving suitable selectivity presents difficulties. Earlier, a test procedure was proposed that allows to measure 36 chromatographic parameters which have been described for characterising stationary phases. This procedure was carried out on 69 reversed-phase liquid chromatography (RP-LC) columns. This paper focuses on the classification of RP-LC stationary phases based on chromatographic parameters. A chemometric study was conducted using 24 parameters that could be measured in a repeatable and reproducible way. Principal component analysis was used to classify the columns and to estimate the minimal number of parameters necessary for a rational classification. It is shown that after reducing the number of parameters from 24 to four or three, similar classifications were obtained. The column classifications were compared to the European Pharmacopoeia stationary phase description and to the column properties obtained from the manufacturers.

Chromatography, Liquid↗

PubMed2003

Ultrasound-assisted extraction of nitropolycyclic aromatic hydrocarbons from soil prior to gas chromatography-mass detection.

Continuous ultrasound-assisted extraction of nitropolycyclic aromatic hydrocarbons from soil prior to their individual separation and determination by gas chromatography (GC) with MS-MS detection is presented here. A multivariate optimisation of the variables affecting the continuous extraction step (namely, probe position, ultrasound radiation amplitude, percentage of duty cycle of ultrasonic exposure, sonication time, total extractant volume, extractant flow rate and temperature of the water-bath in which the extraction cell was placed) was performed. The method was compared with the reference EPA method 3540 using natural contaminated soils. Similar efficiencies were obtained but with a drastic reduction of both the extraction time (10 min versus 24 h) and the extractant volume (less than 10 ml versus 100 ml) by the proposed method. Detection limits of low picogram were obtained, with repeatability and reproducibility between 4.21-5.70 and 5.20-7.23%, respectively.

Gas Chromatography-Mass Spectrometry↗

PubMed1997

Fluidization characteristics of and protein adsorption on fluoride-modified porous zirconium oxide particles.

Porous zirconia particles of specific gravity approximately 3.2 g/ml, mean particle sizes of approximately 50 microns, and terminal settling velocity of approximately 2.8 mm/s in water, were synthesized using an oil emulsion method from 1000 A colloids and were evaluated for their potential use in expanded bed protein adsorption. Expanded beds of particles were stable even for small volume, shallow beds (settled bed: 10 ml, height to diameter ratio < 1.0) and even for fluidization velocities common to much larger particles (210 cm/h for a three-fold bed expansion). When the surface of these particles was modified by fluoride adsorption, the total bed capacity for bovine serum albumin (BSA) adsorption was 42 +/- 2 mg BSA/ml of settled bed volume at linear velocities of 109-210 cm/h. Residence time distribution studies of several solutes under non-binding conditions were performed to assess the degree of liquid mixing and channeling in the expanded bed as a function of fluidization velocity. Liquid mixing and channeling were also studied as a function of distributor design. With these very dense particles, the degree of channeling and mixing did not worsen with the degree of expansion. Elution of adsorbed BSA while the bed was expanded (by a step increase in ionic strength) was rapid resulting in a narrow peak at high fluidization velocities without resorting to settling of the bed. The dynamic binding capacity of BSA at 5% breakthrough (protein effluent concentration equal to 5% of the inlet concentration) was the same for a two-fold expanded bed as for a settled bed (22 +/- 2 mg BSA/ml of settled bed volume), though it decreased for higher bed expansions. BSA binding was reproducible following repeated cleaning of the adsorbent with 0.25 M sodium hydroxide.

Adsorption↗

PubMed1997

Determination of polycyclic aromatic hydrocarbons in waters by use of supercritical fluid chromatography coupled on-line to solid-phase extraction with disks.

The potential of supercritical fluid chromatography (SFC) coupled on-line to solid-phase extraction (SPE) with disks for determining sixteen different polycyclic aromatic hydrocarbons (PAHs) was assessed. A preliminary study of the chromatographic separation was conducted that led to the use of SPE coupled to SFC for improved detection limits. Disks of two different materials, i.e., C18 and polystyrene-divinylbenzene, were assayed in terms of the variables influencing the extraction step. C18 disks provided the best results, with detection limits ranging from 0.1 to 1.5 micrograms l-1. The ensuing method was applied to river and tap water with good repeatability and reproducibility, and no interference from the sample matrix.

Chromatography, Liquid↗

PubMed1998

Assessment of the sample handling procedures in a labor-saving method for the analysis of organochlorine compounds in a large number of fish samples.

A rapid single step clean-up procedure with sulphuric acid oxidation for lipid removal has been assessed by a step-by-step recovery approach for its performance in the analysis of organochlorinated compounds in large numbers of fish samples (muscle). Recovery decreases are essentially due to losses by evaporation but their effect is compensated by correction of the recovery factor of tetrabromobenzene that is used as surrogate. Sample grounding with sodium sulphate provides significant higher concentrations than freeze-drying. Soxhlet extraction for 18 h is sufficient to draw most organochlorine compounds from the samples. Repeatability and reproducibility is smaller than the dispersion between fish of similar length and age from the same lake for all compounds except alpha-hexachlorocyclohexane.

Animals↗

PubMed1999

Peptide separation in normal-phase liquid chromatography. Study of selectivity and mobile phase effects on various columns.

An experimental procedure for peptide separation by normal-phase liquid chromatography (NPLC) was proposed in previous papers. In the present study, the chromatographic behavior of amino, cyano, amide, diol and silica columns, which have been used in non-aqueous NPLC, is investigated anew. The amino column was not appropriate for peptide separation because of poor recovery. The cyano column could not be used due to lack of retention. The amide, diol and silica columns were useful for peptide separation. The chromatograms on amide, diol and silica columns were a little different when the mobile phase composition was changed. The recovery of peptides was good: diol > amide > silica. Repeatability and reproducibility using amide, diol and silica columns was satisfactory.

Amides↗

PubMed1999

Optimization of glucosinolate separation by micellar electrokinetic capillary chromatography using a Doehlert's experimental design.

The aim of this study was to optimize by micellar electrokinetic chromatography the separation of four glucosinolates, i.e. sinigrin, glucobrassicin and methoxyglucobrassicin involved in Cruciferae resistance mechanisms and glucotropaeolin used as an internal standard. The separation borate buffer which contained sodium dodecyl sulphate, tetramethylammonium hydroxide and methanol was firstly optimized by using a three variable Doehlert experimental design. The optimum concentrations found enabled, for the first time, to obtain an acceptable resolution between the two indole glucosinolates, glucobrassicin and methoxyglucobrassicin. Modifications of the method such as a capillary pre-rinse with pure borate buffer and a step change in voltage during experiment were performed to improve the resolutions between glucosinolates and to reduce the analysis time. This method was validated by a statistical analysis and showed good linearity, repeatability and reproducibility.

Buffers↗