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Results for “Repeatability and Reproducibility”

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At least 811 records · Page 45Linked to original sources

PubMedDate not supplied

3M Petrifilm Staph Express Count plate method for the enumeration of Staphylococcus aureus in selected dairy foods: collaborative study.

The 3M Petrifilm Staph Express Count plate method was compared with AOAC Official Method 975.55 for the enumeration of Staphylococcus aureus in selected foods. Five foods--ice cream, raw milk, yogurt, whey powder, and cheese--were analyzed for S. aureus by 12 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample, a low inoculation level, a medium inoculation level, and a medium inoculation level with background flora, each in duplicate. The mean log10 counts for the methods were comparable for all 5 foods. The repeatability and reproducibility variances of the 24 h Petrifilm Staph Express Count plate method were similar to those of the 72 h standard method.

Animals↗

PubMed2004

A sensitive ristocetin co-factor activity assay with recombinant glycoprotein Ibalpha for the diagnosis of patients with low von Willebrand factor levels.

BACKGROUND AND OBJECTIVES: The assay of ristocetin co-factor activity of von Willebrand factor (VWF:RCo) is used in the screening of patients with suspected von Willebrand's disease (VWD), the most frequent inherited bleeding disorder. A correct diagnosis of VWD relies on platelet agglutination tests that have a low accuracy within and between assays. A more accurate VWF:RCo assay would improve VWD diagnosis and classification. DESIGN AND METHODS: We describe here an ELISA method in which a recombinant fragment of the alpha-subunit of platelet glycoprotein Ib-IX-V complex (rGPIbalpha) is bound to an anti-GPIbalpha monoclonal antibody immobilized onto microtiter plate wells and which captures plasma VWF in the presence of ristocetin. The results obtained with this ELISA assay were compared blindly with values calculated from the agglutination test in normal subjects (n=60) and in type 1 (n=8), type 2A (n=16), type 2B (n=13), type 2M (n=17) or type 2M Vicenza (n=8) VWD patients which were characterized by low VWF levels. RESULTS: The two assays gave similar results in both normal subjects and VWD patients (r=0.93), but the ELISA test showed higher sensitivity (0.1 versus 6.25 U/dL). The repeatability and reproducibility gave coefficients of variation of 9% and 10%, respectively, for the ELISA, as compared to 14% and 15% for the agglutination test. INTERPRETATION AND CONCLUSIONS: This ELISA assay can be useful in the identification and classification of VWD patients in that it may provide a more accurate distinction between type 2 with abnormal VWF function and type 1 with a low plasma VWF concentration.

Agglutination Tests↗

PubMed2004

Establishment of European Pharmacopoeia (Ph. Eur.) Biological Reference Preparations (BRP) batch 2 for rDNA hepatitis B vaccine (method A and B).

A collaborative study was initiated by the European Directorate for the Quality of Medicines (EDQM), to assign a potency value for candidate batch 2 of European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for Hepatitis B (rDNA) antigen in vitro assays, for both method A and method B by calibrating them against the Ph. Eur. BRPs, batch 1 for methods A and B respectively. The study was prompted by the observation that the first batch of BRP for method B appeared to have lost potency over time. BRP 1 for method A showed no loss in potency, however stocks of the material were nearing depletion. Eleven laboratories participated in the study and all reported results. Participants performed 3 independent assays using both method A and method B. Method A was used to assess BRPs for method A and method B was used to assess BRPs for method B. Since BRP 1B was suspected to have lost potency, an additional sample was included in the method B test in an attempt to clarify the situation. BRP 1B was also assayed in method A against BRP 1A in the hope of also attaining further information by comparing the results from this study to those obtained in the original study to establish the first batch of BRP [1]. Although it was not the primary aim of this study to correlate in vitro potency with the immunogenicity assay in mice, a number of interested parties also performed the mouse in vivo assay to obtain data on the behaviour of the candidate BRPs in this assay. For method A, potency estimates were satisfactory in terms of repeatability and reproducibility. The candidate material was therefore assigned a value of 16.6 micrograms/ml. For method B, it appeared that the observation of reduced in vitro potency of BRP1 was confirmed. Despite the attempt to clarify the situation with additional studies, it was not possible to assign a potency value with the results obtained. A small-scale collaborative study will be organised to determine an appropriate value for the candidate BRP for method B. The results from the in vivo study while highly variable showed no evidence of a shift in the in vivo potency for either BRP 1A or BRP 1B. It should be noted that the in vitro method for determination of hepatitis B vaccine potency is under revision due to the discontinuation of the Auszyme kit from Abbott, which is required to perform the current assays. Once an alternative assay has been established, the suitability of the reference preparations or establishment of new reference preparations will be required. The candidate material for method A BRP was adopted by the European Pharmacopoeia Commission at its session in November 2003, as the European Pharmacopoeia Hepatitis B vaccine (rDNA) method A, batch 2.

Animals↗

PubMed2004

Derivative-differential UV spectrophotometry and compensation technique for the simultaneous determination of zidovudine and lamivudine in human serum.

Three new simple, precise, rapid and selective determination methods are described for zidovudine (ZID) and lamivudine (LAM) in human serum and in pharmaceutical formulations. The first method, based on the compensation technique is presented for the derivative spectrophotometric determination of binary mixtures with overlapping spectra. Using ratios of the derivative maxima or the derivative minimum, the exact compensation of either component in the binary mixture and human serum can be achieved, followed by its determination. The second method, differential derivative spectrophotometry, comprised of measurement of the difference absorptivities derivatized in the first order (deltaD1) of a tablet extract in 0.1 N NaOH relative to that of an equimolar solution in methanol at wavelengths of 246 nm and 263 nm, respectively. Neither sample pretreatment nor separation were required. The third method is based on HPLC on a reversed-phase column using a mobile phase of 0.01M sodium dihydrogen phosphate : methanol : acetonitrile (4 : 2 : 3 v/v/v), with detection at 285 nm. Repeatability and reproducibility studies for each compound showed no significant differences at 95% confidence level. The proposed methods were used for the simultaneous determination of the drugs in human serum samples and binary mixtures with good recoveries.

Adult↗

PubMed2004

Determination of nanogram level of VSCs using GC-SCD and an adsorption tube.

A quantitative analytical method was used for detection of low level of volatile sulfur compounds (VSCs) using GC with a sulfur chemiluminescence detector (SCD) in this study. A linear response over the range of 2-90 ngS injected was obtained with a good repeatability or reproducibility. Equimolar response for H2S, DMS, MeSH, and EtSH was obtained by use of SCD and the response of the SCD is nearly equimolar for different sulfur compounds. It was possible to quantify the total VSCs as well as individual VSC using one of the standard VSCs. VSC recovery was measured with respect to some storing methods. An adsorption tube packed with molecular sieve 5A showed almost perfect recovery for both H2S and dimethyl sulfide (DMS) during 6 days at a dark state below 2 degrees. Whereas, with a gas tight pyrex vial or tedlar bag, it was impossible to obtain the recovery of 50% after 6 days. It is strongly recommended to use the adsorption tube for determination of nanogram levels of volatile sulfur compounds and for storing and concentrating VSCs effectively with a minimum experimental error.

Adsorption↗

PubMed2004

Determination of musks and other fragrance compounds at ng/L levels using CLSA (closed loop stripping analysis) and GC/MS detection.

Closed loop stripping analysis (CLSA), a suitable tool for the determination of volatile and semivolatile compounds at low trace levels (ng/l), has been used to determine and quantify seven selected musks and two fragrances (Acetyl cedrene and Amberonne). The obtained extracts are analyzed by high resolution gas chromatography coupled to mass spectrometry (GC/MS) operating in the SIM mode. Quality parameters such as limit of detection; matrix effects; precision expressed as repeatability and reproducibility relative standard deviations of the method and an estimation of the uncertainty have been evaluated. The method has been applied to the analysis of wastewater effluents, surface water and tap water from different places in Europe. All samples contained differents musks at ng/l levels with the polycyclic musks Galaxolide and Tonalide and both fragrances, Amberonne and Acetyl cedrene, being the most abundant. These results suggest the importance of studying and controlling the presence of these ubiquitous environmental compounds in water systems.

Fatty Acids, Monounsaturated↗

PubMed2004

HPLC profiling and quantification of active principles in leaves of Hedera helix L.

Ivy (Hedera helix L., Araliaceae), is an evergreen medicinal and ornamental plant. Depending on leaf polymorphism different shaped ivy leaves were extracted and subsequently analyzed by reversed-phase high performance liquid chromatography (RP-HPLC). Quantitative determination of its most prominent saponins hederacoside C (1) and alpha-hederin (2) from different ivy leaf extracts were detected, validated and optimized for quick profiling. The linearity of response, repeatability and reproducibility of the applied RP-HPLC method are reported.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

Determination of metal concentration in fat supplements for swine nutrition by atomic absorption spectroscopy.

The presence of some essential and toxic metals in fat supplements for swine diet was investigated. Collected samples represented a relevant production of the Italian industry. In particular, some samples were enriched with antioxidants or waste cooking oils. The method for the determination of Ca, Cu, Cd, Fe, Mg, Mn, Ni, Pb, and Zn in fat samples was developed by means of a certified reference material (CRM 186) and a representative fatty sample (RFS). All samples were digested in closed vessels in a microwave oven and then analyzed by flame atomic absorption or graphite furnace atomic absorption spectrometry. The entire analytical method provided a satisfactory repeatability and reproducibility confirmed by agreement between the experimental recovery data obtained for the CRM 186 sample and, with the method of standard additions, for the RFS material. The samples generally showed a small amount of metals compared with the recommended daily intake for the essential elements. On the other hand, some samples contained a significant concentration, from an analytical point of view, of Cd, Ni, and Pb. Principal component analysis (PCA) was applied to inspect the experimental data obtained from samples analysis. Basically no differences were detected in terms of metal concentration among the fat supplements analyzed.

Animal Feed↗

PubMed2001

Assessment of the fouling potential of wastewater treatment plant effluent using a modified capillary suction time measurement.

A new technique was developed to measure membrane fouling, which is derived from the capillary suction time (CST)--a parameter often used to indicate the dewaterability of sludge--and which is called the modified CST (CSTm). The results indicate a good repeatability and reproducibility of the test. Spiking tests with suspended solids and humic acid, which have a high fouling potential, resulted in a significant rise of the CSTm value, indicating a sensitive assessment of these fouling components. However, the CSTm measurement is mainly indicative for the colloidal fouling of the sample.

Capillary Action↗

PubMed2005

Genetic characterization of Indian-origin and Chinese-origin rhesus macaques (Macaca mulatta).

Genetic differences between Indian-origin and Chinese-origin rhesus macaques are as great as those between some primate species and can influence the results of experiments in which both are used as animal models for the study of the same human diseases. Unfortunately, many breeding facilities do not know with certainty the origin of the founders of their rhesus breeding colonies. Here I summarize the most definitive of the genetic traits among the microsatellite (STR) loci and mitochondrial DNA sequences that my laboratory previously reported to characterize Indian-origin and Chinese-origin rhesus macaques and then estimate the frequencies of these traits and their reliability as indicators of country of origin. The expression of diagnostic traits at two or more of four different unlinked loci provides a nearly 100% reliability in distinguishing rhesus macaques of Indian and Chinese origin.

Animals↗

PubMed2005

[Methods for the evaluation of bone regeneration during distraction osteogenesis].

During limb lengthening gradual reconstruction of bone tissue in distraction gap requires constant, systematic control and evaluation. This process is depicted descriptively and subjectively. Changes happening during osteogenesis are dynamic, they can stop, slow down or accelerate, and regenerate may be of various shape and form. In this work different methods of bone regenerate evaluation are presented. They may be divided on two basic groups. First group contains methods with X-radiation, and the second - without X-rays. Examinations that evaluate arising bone regenerate may be also divided on descriptive examinations and quantitative. Despite that different methods are used for distraction osteogenesis course estimation, classic radiological examination remains the basic one. The rest of them are most often supplementary examinations, useful in selected stages of treatment, for e.g. ultrasonography in first stage of regenerate arising. So it seems, that future is in quantitative regenerate evaluation using radiographs. Classic X-ray picture made in reproducible and repeatable conditions may be subjected to digital, quantitative image analysis, and acquired results enables for more precise and more balanced evaluation of new bone formation in distraction osteogenesis.

Bone Regeneration↗

PubMedDate not supplied

Enumeration of total coliforms and E. coli in foods by the SimPlate coliform and E. coli color indicator method and conventional culture methods: collaborative study.

The relative effectiveness of the SimPlate Coliform and E. coli Color Indicator (CEc-CI) method was compared to the AOAC 3-tube Most Probable Number (MPN) methods for enumerating and confirming coliforms and Escherichia coli in foods (966.23 and 966.24). In this study, test portions were prepared and analyzed according to the conditions stated in both the AOAC methods and SimPlate directions for use. Six food types were artificially contaminated with coliform bacteria and E. coli: frozen burritos, frozen broccoli, fluid pasteurized milk, whole almond nut meats, cheese, and powdered cake mix. Method comparisons were conducted. Overall, the SimPlate method demonstrated <0.3 log difference for total coliform and E. coli counts compared to the AOAC reference methods for the majority of food types and levels analyzed. In all cases, the repeatability and reproducibility of the SimPlate CEc-CI method were not different from those of the reference methods and in certain cases, were statistically better than those of the AOAC 3-tube MPN methods. These results indicate that the SimPlate CEc-CI method and the reference culture methods are comparable for enumeration of both total coliforms and E. coli in foods.

Colony Count, Microbial↗

PubMed2005

Determination of fragrances at ng/L levels using CLSA and GC/MS detection.

Polycyclic and nitro musks and two fragrances (Acetyl cedrene and Amberonne) have been determined and quantified in influent and effluent waste water, river water and tap water samples from different European countries by closed loop stripping analysis (CLSA) as a method of preconcentration and GC/MS operating in the SIM mode. Limits of detection; precision expressed as repeatability and reproducibility relative standard deviations of the method; matrix effects and the estimation of the uncertainty have been evaluated. All samples contained different musks at ng/l levels being the polycyclic musks Galaxolide and Tonalide and both fragrances, Amberonne and Acetyl cedrene the most abundant. Removal of these main compounds is achieved partially in all waste water treatment plants studied. These results suggest the importance of studying and controlling the presence of these ubiquitous environmental compounds in water systems.

Benzopyrans↗

PubMedDate not supplied

Stability study of simvastatin under hydrolytic conditions assessed by liquid chromatography.

In this work, a liquid chromatography stability-indicating method was developed and applied to study the hydrolytic behavior of simvastatin in different pH values and temperatures. The selected chromatographic conditions were a C18 column; acetonitrile-28 mM phosphate buffer solution, pH 4 (65 + 35) as the mobile phase; 251 degrees C column temperature; and flow rate 1 mL/min. The developed method exhibited an adequate repeatability and reproducibility (coefficient of variation 0.54 and 0.74%, respectively) and a recovery higher than 98%. Furthermore, the detection and quantification limits were 9.1 x 10(-7) and 2.8 x 10(-6) M, respectively. The degradation of simvastatin fitted to pseudo-first order kinetics. The degradation was pH dependent, being much higher at alkaline pH than at acid pH. Activation energy, kinetic rate constants (k) at different temperatures, the half life (t1/2) and the time for 10% degradation to occur (t90) values are also reported.

Acetonitriles↗

PubMedDate not supplied

Liquid chromatographic determination of fosthiazate residues in environmental samples and application of the method to a fosthiazate field dissipation study.

A method was developed and validated for the determination of residues of the organophosphorus nematicide fosthiazate in soil and water by using reversed-phase liquid chromatography with UV detection. Good recoveries (>85%) of fosthiazate residues were obtained from water samples (drinking water, groundwater, and liquid chromatography water) after passage of 0.5-2 L water through solid-phase extraction (SPE) C-18 cartridges and subsequent elution with ethyl acetate. Residues in soil were extracted with methanol-water (75 + 25, v/v) on a wrist-action shaker, and the extract was cleaned up on C-18 SPE cartridges before analysis. The method was validated by analysis of a range of soils with different physicochemical characteristics; recoveries exceeded 87% at fortification levels ranging from 0.02 to 5.0 mg/kg. The precision values obtained for the method, expressed as repeatability and reproducibility, were satisfactory (<11%). Fosthiazate detection limits were 0.025 microg/L and 0.005 mg/kg for water and soil samples, respectively. The decline in the levels of fosthiazate residues in soil was measured after application of fosthiazate to protected tomato cultivation. The dissipation of fosthiazate residues followed first-order kinetics with a calculated half-life of 21 days.

Acetates↗

PubMedDate not supplied

Youden analysis of Karl Fischer titration data from an interlaboratory study determining water in animal feed, grain, and forage.

Data from a recent interlaboratory study of the determination of water (moisture) in animal feed, grain, and forage (plant tissue) by Karl Fischer titration were re-analyzed using Youden plots. The purpose was to show the unique ability these plots possess of separating random and systematic errors visually while providing numerical estimates of the precision and the systematic error of the method. Furthermore, the usefulness of the technique is underscored because AOAC INTERNATIONAL allows the use of matched pairs in collaborative studies to obtain estimates of repeatability and reproducibility.

Animal Feed↗

PubMed2006

Determination of the antihyperlipidemic simvastatin by various voltammetric techniques in tablets and serum samples.

The electrochemical behavior and determination of simvastatin (SMV), a lipid-lowering drug, were studied in aqueous alcohol medium at a stationary glassy carbon electrode. Cyclic voltammetry studies showed one main, well-defined, sharp oxidation peak between pH 2 and 8. The oxidation was irreversible and exhibited a diffusion controlled mechanism. Differential pulse and square wave voltammetric methods for the quantitative determination of SMV in pharmaceutical dosage forms and spiked serum samples were developed based on the linear relationship between the peak current and the concentration. Differential pulse and square wave voltammetric techniques for the determination of SMV in 0.1 M H2SO4 and a constant amount of methanol (20%), which allow quantitation over the 2 x 10(-6)-1 x 10(-4) M range in supporting electrolyte with a detection limit of 2.71 x 10(-7) M and 5.50 x 10(-7) M for differential pulse and square wave voltammetric methods, respectively, are proposed. The repeatability and reproducibility of the methods were determined. Precision and accuracy were also checked. These methods were used for the determination of SMV in tablets. The standard addition method was used in biological media. No electroactive interferences from endogenous substances and excipients were found in biological fluids and pharmaceutical dosage forms, respectively.

Algorithms↗

PubMed2006

Electrochemical methods for determination of the protease inhibitor indinavir sulfate in pharmaceuticals and human serum.

Indinavir sulfate is an inhibitor of the human immunodeficiency virus (HIV) protease. The aim of this study was to determine indinavir levels in serum and pharmaceuticals, by means of electrochemical methods using the hanging mercury drop electrode (HMDE). Indinavir exhibited irreversible cathodic waves over the pH range 2.00-12.00 in different supporting electrolytes. The current-concentration plot was rectilinear over the range from 8 x 10(-7) M to 8 x 10(-6) M with a correlation coefficient of 0.996 for differential pulse voltammetry (DPV) and 8 x 10(-7) M to 1 x 10(-5) M with correlation of 0.999 M for osteryoung square ware voltammetry (OSWV) in Britton-Robinson buffer at pH 10.00. The wave was characterized as being irreversible and diffusion-controlled. The proposed methods were fully validated and successfully applied to the determination of indinavir in capsules and spiked human serum samples with good recoveries. The repeatability and reproducibility of the methods as well as precision and accuracy (such as supporting electrolyte, serum samples) were determined. No electroactive interferences from the endogenous substances were found in serum samples.

Capsules↗