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Results for “Repeatability and Reproducibility”

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At least 613 records · Page 34Linked to original sources

PubMed2001

The electronic nose as a rapid sensor for volatile compounds in treated domestic wastewater.

An electronic nose consisting of 12 metal oxide sensors was used to monitor volatile compounds in effluent of a domestic wastewater treatment plant. Effluent and reference (deionized water) samples were heated to 60 and 90 degrees C to promote the volatilization and to increase the sensitivity. An effluent measuring campaign of 12 weeks was conducted and the repeatability and reproducibility of the procedure and the apparatus were determined. Processing the obtained fingerprints with principal component analysis (PCA) allowed interpretation and differentiation of the samples in terms of origin and quality, relative to the reference. To minimize the variance due to sensitivity fluctuations of the apparatus and to detect effluents with deviating qualities, two new concepts were defined, i.e. the relative sensorial odour perception (in short: rSOP) and the relative fingerprint. Correlations between the relative overall electronic nose output, expressed as rSOP, and selected routine parameters were weak except for the parameter "volatile suspended solids" (VSS), indicating adsorption of volatile organic compounds (VOCs) onto the organic particles. The results clearly demonstrate the possibility to use the electronic nose as a rapid alarm generator towards volatile compounds, e.g. in specific advanced treatment processes to produce reclaimed water from effluent of the domestic wastewater treatment plant under scrutiny.

Adsorption↗

PubMed2002

Comprehensive study on dioxin contents in binder and anti-caking agent feed additives.

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in some additives widely employed as binder and anti-caking agents in feedstuffs, such as kaolin, bentonite, zeolite, etc. with an special attention on sepiolite samples. Owing to their physico-chemical properties, the little information of these materials reported in the literature, the variability of PCDDs/PCDFs found in a preliminary evaluation and the absence of reference materials highlighted further research needed. Therefore, an extensive study on the analytical procedures based on the classical methods was performed with sepiolite samples. The study includes evaluation of reproducibility and repeatibility. To this end, a series of intra-day and nine inter-day analysis were made. The methodolgy was also assessed against the sample size and series of 12.5, 25, 37.5 and 50 g were analyzed. In all cases, the results confirmed good correlation with the parameters evaluated.

Animal Feed↗

PubMed1983

The lectin neuraminidase inhibition test: a new method for the detection of antibodies to neuraminidase.

Two methods for the detection of neuraminidase antibodies were compared. The lectin neuraminidase inhibition test (LNI-test) gave results comparable with those provided by the conventional neuraminidase inhibition test (NI-test). Reproducibility and repeatability were better with the LNI-test which used smaller amounts of materials, was less time consuming than the NI-test and was more sensitive.

Animals↗

PubMed2000

Proficiency-testing issues relating to sirolimus.

BACKGROUND: A need exists to document laboratory proficiency to (1) compare results produced by different analytical techniques and (2) ensure consistency of results from multiple testing sites. OBJECTIVES: To enable concentration-controlled studies of sirolimus to proceed with confidence, proficiency-testing schemes were put in place at laboratories selected to act as reference laboratories. The feasibility of establishing an ongoing proficiency-testing scheme was addressed with respect to sample stability. The scheme was then used to test proficiency for the measurement of sirolimus in 3 blinded samples each month. METHODS: The method chosen for measurement of sirolimus was a prototype microparticle enzyme immunoassay. Initially, 15 laboratories were asked to analyze a series of 85 blinded samples that tested their inaccuracy, repeatability, and reproducibility for the measurement and their ability to dilute over-range samples competently. Both blood samples spiked with sirolimus and pooled blood samples from patients receiving the drug were circulated to a maximum of 50 laboratories. RESULTS: Overall, both inaccuracy and imprecision were acceptable by predefined criteria. Inaccuracy for the immunoassay (percentage difference of the measured value against the nominal value) averaged -5% (95% CI, -9% to -1%). The mean percentage difference between the immunoassay and a high-performance liquid chromatographic assay with mass-spectrometric detection for the measurement of sirolimus in pooled samples (n = 5) from patients receiving the drug was 29% (95% CI, 24% to 34%). CONCLUSION: The techniques documented here as part of the International Sirolimus Proficiency Testing Scheme could be applied to other clinical studies requiring protocol-driven dosing adjustments based on sirolimus measurements, irrespective of analytical technique used.

Chromatography, High Pressure Liquid↗

PubMed2001

A practical three-dimensional reconstruction method to measure the volume of the sexually-dimorphic central nucleus of the medial preoptic area (MPOC) of the rat hypothalamus.

Published estimates of the volume of the sexually-dimorphic central nucleus of the medial preoptic area (MPOC) have been quite variable both within and between laboratories. To obtain MPOC volume, most experimenters began with a two-dimensional (2-D) approach. They outlined the MPOC on each of several individual sections; then they added up the area contained on each section and multiplied the total by the section thickness. A 3-D reconstruction approach, although promising, has been somewhat impractical until recently due to the requirements for highly specialized software and massive computing support. Here, we describe the application of commercially-available PC-based software to measure MPOC volume by 3-D reconstruction. Male and female Sprague-Dawley rats, 24 or 50 days of age, were perfusion-fixed with 10% neutral phosphate-buffered formaldehyde. Following processing and embedding, a series of 20-microm sagittal paraffin sections were cut and mounted onto slides. After staining with cresyl violet, they were digitized using a microscope-mounted video camera connected to a frame-grabber in a Pentium-class computer (MCID-M5+). In addition to the MPOC, the anterior commissure, fornix, paraventricular nucleus, medial division of the bed nucleus of the stria terminalis, third ventricle and the bed nucleus of the anterior commissure were identified on the screen image and outlined using a computer mouse. These outlines were then aligned and rendered in 3-D with a solid overlay. The additional areas, such as anterior commissure, form landmarks within 3-D space to improve the accuracy with which the MPOC may be located and outlined. The reconstruction provides a striking illustration of the geometric relations between the structures of the anterior hypothalamus in the male and female rat. Moreover, the volumes determined from the overlays were reproducible between repeated studies in our laboratory. Our volume measurements confirm the sexual dimorphism previously reported for MPOC volumes, and provide a relatively quick, accurate and reliable protocol that should be useful in future experimental studies of environmental estrogenic compounds.

Animals↗

PubMed2001

Development of a real-time PCR procedure including an internal control for the measurement of HCMV viral load.

Human cytomegalovirus (HCMV) infections are frequent in immuno-compromised patients. The recent development of real-time PCR procedures that allow the rapid quantification of genome load will be helpful for accurate monitoring of these infections. Two extraction procedures were evaluated using 30 blood samples that were processed pure and diluted (1/10). Repeatability and reproducibility of the quantitative PCR procedure using an internal control for amplification were analysed, and its sensitivity compared to a qualitative PCR procedure using 50 HCMV culture positive blood samples. The real-time PCR and qualitative PCR procedures were positive in 46 and 48 of the samples tested, respectively. Discrepancies were observed for samples with a low viral load. The sensitivity of the real-time PCR procedure was evaluated at 500 HCMV DNA copies per ml of sera. The use of an internal control concomitantly processed during the HCMV quantification did not alter the sensitivity of the procedure, and was relevant for the detection of putative PCR inhibitors that may interfere with the amplification process. This procedure was used to measure genome load in two bone marrow transplant patients with HCMV disease, confirming that this new PCR procedure should be used widely for diagnosing and monitoring HCMV infections in transplant patients.

Bone Marrow Transplantation↗

PubMed2003

A novel spectrofluorometric microassay for Streptococcus mutans adherence to hydroxylapatite.

Adherence to the tooth surface by Streptococcus mutans is an important step in initiation of dental caries. Current in vitro methods used to study bacterial adherence are time-consuming and may involve the use of radiolabels. The aim of this study was to develop a more convenient, high-throughput, microtitre-plate assay of bacterial adherence to hydroxylapatite. S. mutans was labelled with the fluorescent indicator BCECF/AM and fluorescence measured using a spectrofluorometer. Fluorescence microscopy confirmed label uptake. Optimal labelling occurred at 120 min with 50 microM BCECF/AM in DMSO. Viability was similar in control untreated bacterial cells, bacteria treated with DMSO alone or with the label for up to 4 h. Preliminary adherence experiments were performed using four commercially available types of hydroxylapatite. Fluorescence from pre-labelled bacteria was measured for bound cells. The assay was then optimised with respect to time and bacterial concentration using Fluka crude hydroxylapatite. Time course studies demonstrated that adherence reached saturation by 30 min incubation when using 1x10(7) cfu/ml labelled bacteria to 1 mg hydroxylapatite, coated with PBS or saliva. The fluorescence-based adherence assay was highly reproducible in repeated analyses and was useful in demonstrating interference with adherence. In conclusion, this microtitre-plate assay offers a more convenient approach to examine streptococcal adherence and could be used to screen for potential anti-adhesive agents.

Bacterial Adhesion↗

PubMed2002

Analysing collaborative trials for qualitative microbiological methods: accordance and concordance.

In qualitative (detection) food microbiology, the usual measures of repeatability and reproducibility are inapplicable. For such studies, we introduce two new measures: accordance for within laboratory agreement and concordance for between laboratory agreement, and discuss their properties. These measures are based on the probability of finding the same test results for identical test materials within and between laboratories, respectively. The concordance odds ratio is introduced to present their relationship. A method to test whether accordance differs from concordance is discussed.

Food Microbiology↗

PubMed1998

Prevalence and growth of Listeria monocytogenes in naturally contaminated seafood.

Listeria monocytogenes contamination of seafood varies with product category. The highest prevalence was found in cold-smoked fish (34-60%), while the lowest was found in heat-treated and cured seafood (4-12%). The prevalence of L. monocytogenes differed greatly in cold-smoked salmon between production sites, ranging from < 1.4% (nil out of 70 samples) to 100%. The prevalence at the individual production sites was reproducible at repeated sampling. The results indicate that it is possible to produce cold-smoked salmon with a low prevalence of L. monocytogenes. The organism showed moderate growth in naturally contaminated cold-smoked, and 'gravad', fish while the growth appeared faster in hot smoked fish. Thus L. monocytogenes is not under control in these products. Finally, the prevalence and growth of L. monocytogenes in naturally contaminated cold-smoked salmon are discussed in relation to controlling this risk.

Animals↗

PubMed1998

A novel, selective synthetic acetamide containing culture medium for isolating Pseudomonas aeruginosa from milk.

A selective synthetic medium has been developed both in liquid (Z-broth) and solid (Z-agar) forms for selective isolation of Pseudomonas aeruginosa from foods. The simple, easy to prepare peptone-free synthetic medium contained acetamide that is metabolized to ammonia and acetic acid providing nitrogen and carbon supply. The medium contained no inhibitors. Selectivity of the liquid medium was tested by inoculation of pure cultures of different bacteria belonging to the groups Bacillus, Pseudomonas, Enterobacteriaceae and Staphylococcus. It was found that the selectivity of the medium was complete for the examined range of bacteria. However, a similar result was obtained when nitrofurantoin broth was used. Applicability of the synthetic agar medium was also tested by a nation-wide inter-laboratory test using two milk samples containing 10(3)/ml (sample I) and 10(5)/ml (sample II) Pseudomonas aeruginosa. According to this test, no microbiologically relevant differences were found between the results obtained by Z-agar and cetrimide-agar a frequently used selective agar in case of sample II. However, a relevant and statistically significant difference was found in the results of sample I in favour of the Z-agar, that could indicate the presence of a low number of bacteria. Concerning repeatability and reproducibility, Z-agar proved to be superior to cetrimide agar.

Acetamides↗

PubMed2003

The 10 basic requirements for a scientific paper reporting antioxidant, antimutagenic or anticarcinogenic potential of test substances in in vitro experiments and animal studies in vivo.

There is increasing evidence that chemicals/test substances cannot only have adverse effects, but that there are many substances that can (also) have a beneficial effect on health. As this journal regularly publishes papers in this area and has every intention in continuing to do so in the near future, it has become essential that studies reported in this journal reflect an adequate level of scientific scrutiny. Therefore a set of essential characteristics of studies has been defined. These basic requirements are default properties rather than non-negotiables: deviations are possible and useful, provided they can be justified on scientific grounds. The 10 basic requirements for a scientific paper reporting antioxidant, antimutagenic or anticarcinogenic potential of test substances in in vitro experiments and animal studies in vivo concern the following areas: (1) Hypothesis-driven study design; (2) The nature of the test substance; (3) Valid and invalid test systems; (4) The selection of dose levels and gender; (5) Reversal of the effects induced by oxidants, carcinogens and mutagens; (6) Route of administration; (7) Number and validity of test variables; (8) Repeatability and reproducibility; (9) Statistics; and (10) Quality Assurance.

Animals↗

PubMed1997

Evaluation of an ELISA for the routine diagnosis of Dictyocaulus viviparus infections in cattle.

An enzyme-linked immunosorbent assay (ELISA) that detects antibodies against Dictyocaulus viviparus in experimentally and naturally infected cattle was evaluated for its sensitivity, specificity, the moment of seroconversion and persistence of the anti-D. viviparus response and precision. The first three parameters were compared with those of an indirect haemagglutination assay (IHA). Specificity and sensitivity of both assays were assessed in sera collected from calves experimentally infected with pure isolates of D. viviparus, Ostertagia ostertagi, Cooperia oncophora, Nematodirus helvetianus, Ascaris suum or Fasciola hepatica, and from parasite-naive calves. The specificity of both the ELISA and IHA was very high, 99.2% and 99.6%, respectively. The sensitivity of the ELISA (100%) was significantly higher than that of the IHA (78.1%). In experimentally infected cattle, D. viviparus-specific antibodies were first detected with the ELISA between days 28 and 42 post-infection (p.i.), whereas the IHA only became positive between days 42 and 70. With the ELISA, antibody levels persisted until day 168 p.i. The IHA remained positive until the end of the experiment (day 196). None of the vaccinated animals were seropositive with the ELISA, whereas 25% of the calves were seropositive with the IHA. The seroprevalence of D. viviparus infections was determined in a field study with 467 sera from cattle of 64 herds; 227 (48.6%) of the animals were seropositive with the ELISA whereas only 38 (8.1%) scored positive with the IHA. To determine the precision of the ELISA, a total of five laboratories participated in trials, in which panels of strong positive, positive, and weak positive candidate sera were tested blind according to an international (International Standard ISO 5725, 1986) standard procedure. The repeatability and reproducibility of the ELISA were 0-16% and 14-26%, respectively. After these promising results it was decided to introduce this ELISA in 1995 as a routine test in all Animal Health Services in the Netherlands, replacing the IHA and faecal examinations for lungworm.

Animals↗

PubMed2001

Simultaneous quantitation of ephedrines in urine by gas chromatography-nitrogen-phosphorus detection for doping control purposes.

A gas chromatographic method for the simultaneous quantitation of ephedrine, pseudoephedrine, norephedrine (phenylpropanolamine), norpseudoephedrine (cathine) and methylephedrine in urine is described. The method consists of a liquid-liquid extraction with tert.-butyl methyl ether at pH 14. The extracts are analysed on a GC system equipped with an Rtx-5 Amine column and a nitrogen-phosphorus detector. Method validation shows excellent separation, linearity, specificity, accuracy, precision, intra-laboratory repeatability and reproducibility, making the method especially suitable for quantitation of ephedrines in urine samples for doping control purposes. A statistical analysis on the abuse of the different ephedrines in urine from athletes controlled in the Flemish doping control laboratory during the period 1993-2000 is included.

Calibration↗

PubMed1997

Determination of haloperidol and its reduced metabolite in human plasma by liquid chromatography-mass spectrometry with electrospray ionization.

A sensitive and accurate liquid chromatographic-electrospray mass spectrometric (LC-ES-MS) method for the determination of haloperidol (H) and reduced haloperidol (RH) in human plasma is presented, using chlorohaloperidol as the internal standard. A 2-ml volume of plasma was subjected to basic (NaOH) extraction, acid (HCl) back-extraction, acid wash and basic (NaOH) re-extraction. The extraction solvent was hexane-isoamyl alcohol (99:1, v/v) for the whole procedure. A Nucleosil C18 column (150 x 1 mm) was used for high-performance liquid chromatography, together with 2 mM HCOONH4-acetonitrile (55:45, v/v; pH 3.0) as the mobile phase. For each drug, four characteristic ions were monitored. Linearity was assessed in the ranges 0.1-50 and 0.25-50 ng/ml for H and RH, respectively. Recoveries were 58 and 70% and detection limits were 0.075 and 0.100 ng/ml for H and RH, respectively. Correlation coefficients were better than 0.999 for both compounds. R.S.D.s for repeatability and reproducibility at 0.25 ng/ml were 11.1 and 8.5% for H and 9.4 and 11.2% for RH, respectively. One of the main advantages of (LC-ES-MS) over other detection systems is the increase in selectivity obtained by monitoring three ions of confirmation for each of the drugs.

Antipsychotic Agents↗

PubMed1997

Automated high-performance liquid chromatographic method for the analysis of two novel ergoline compounds in human plasma.

A rapid and sensitive high-performance liquid chromatographic method for the determination of the novel ergoline derivatives sergolexole (compound I), its acid metabolite (compound II) and cis-n-(2-hydroxycyclopentyl)-6-methyl-1-(1-methylethyl)ergoline-8- carboxamide (LY215840, compound III) in human plasma is reported. The compounds were extracted from plasma by automated solid-phase extraction and analysed on a reversed-phase C8 column with fluorescence detection. The limit of quantification for all compounds was 10 ng/ml and the response was linear over the range 10-1000 ng/ml. Validation studies showed the method to be both repeatable and reproducible with no interference from human plasma. The method has been used to support pharmacokinetic studies and has proved to be robust and effective.

Chromatography, High Pressure Liquid↗

PubMed1997

Sensitive microanalysis of imipramine and desipramine in single rat thyroids by gas chromatography-mass spectrometry.

A new sensitive method for the quantitative determination of imipramine and desipramine in single rat thyroids using gas chromatography-mass spectrometry with selected ion monitoring, after enzymatic hydrolysis and liquid-liquid extraction has been developed. The technique was deemed suitable for microanalysis of single rat thyroids and for other solid tissues, using smaller sample sizes than usually required for traditional determination methods. The quantification was linear from 10 to 200 nmol/l (i.e., from 0.25 to 5 microg/g) for imipramine and from 100 nmol/l to 2000 nmol/l (i.e., from 2.4 to 47 microg/g) for desipramine, and the limits of detection (less than 25 ng/g tissue for both compounds) were better than those previously reported. Recoveries, repeatability and reproducibility of this technique were satisfactory. It has been successfully applied in a preliminary study of the concentration-time profiles of imipramine and desipramine in the thyroid of rats treated with either of these drugs.

Animals↗

PubMed1998

Interlaboratory study of the analysis of benzylpenicillin by liquid chromatography.

A liquid chromatography method for analysis of benzylpenicillin was examined in a collaborative study involving seven laboratories. The method comprised an isocratic part, which is used in the assay. The isocratic part corresponds to the assay method for benzylpenicillin used by a manufacturer. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Five samples of benzylpenicillin (sodium and potassium salts) were analysed. The main component and the impurities were determined. An analysis of variance proved the absence of consistent laboratory bias. The laboratory-sample interaction was not significant. Estimates for the repeatability and reproducibility of the method, expressed as standard deviations (S.D.) of the result of the determination of benzylpenicillin, were calculated to be 0.71 and 0.80, respectively.

Analysis of Variance↗

PubMed1999

Analysis of ergovaline in milk using high-performance liquid chromatography with fluorimetric detection.

A high-performance liquid chromatographic method for the determination of the mycotoxin ergovaline in goat's milk is described here. Ergotamine was used as an internal standard. For a sample size of 5.0 ml, the cleanup method included precipitation of milk protein with acetone. Then, ergovaline was extracted twice with chloroform and purified by elution on an Ergosil column. HPLC separation of the extract was accomplished on a C18 column: an isocratic elution, using acetonitrile-ammonium carbonate, was performed, and the analyte was detected by fluorimetry. The method was found to be linear between 0.7 and 8 ng ml(-1), a mean recovery rate of 99.8% was obtained, and the described assay appeared both repeatable and reproducible. The limit of detection and the limit of quantitation of ergovaline in milk were 0.2 ng ml(-1) and 0.7 ng ml(-1), respectively. In order to apply the proposed method, four lactating goats were administered the toxin intravenously at a dose of 32 mg kg(-1) body weight. The concentrations of the drug in plasma and milk were then determined at standardized intervals. Ergovaline (unequivocally identified by LC-MS-MS) could not be detected in the milk beyond eight hours post-dosing. Therefore, in goats, milk does not appear to be a major excretion route for the unmetabolized toxin.

Animals↗