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Results for “Repeatability and Reproducibility”

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PubMed1979

Stability-indicating high-performance liquid chromatographic determination of chlorpropamide, tolbutamide, and their respective sulfonamide degradates.

A quantitative high-performance liquid chromatographic method for the determination of chlorpropamide, tolbutamide, and their respective hydrolysis products, p-chlorobenzenesulfonamide and p-toluenesulfonamide, in solid dosage forms was developed. The method is stability indicating and can be used to determine the sulfonamide hydrolysis product and the intact drug in the presence of minor degradates. Method reproducibility, demonstrated by repeated injections of a calibration standard, was 1.21%. The lower limit of quantitation of the hydrolysis products, p-chlorobenzenesulfonamide and p-toluenesulfonamide, was 0.2 microgram/5-microliter injection. The accuracy of the method for intact drugs was determined by comparison of the HPLC results to those obtained by the appropriate USP or BP assays. The mean of the results obtained by the two methods differed by 0.7% for chlorpropamide and 0.3% for tolbutamide. Pure drug samples were spiked with amounts of the hydrolysis products ranging from 20 to 120% of the intact content. The mean percent recovery for p-chlorobenzenesulfonamide was 98.6%; for p-toluenesulfonamide, it was 100.6%. A qualitative TLC procedure for the detection of chlorpropamide, p-chlorobenzenesulfonamide, dipropylurea, propylurea, n-propylamine, tolbutamide, p-toluenesulfonamide, dibutylurea, butylurea, and n-butylamine is also described.

Chlorpropamide↗

PubMed2002

Mapping at glomerular resolution: fMRI of rat olfactory bulb.

The rat olfactory bulb contains approximately 2000 functional units called glomeruli which are used to recognize specific characteristics of odorants. Activity localization of individual glomerulae ( approximately 0.002 microL) has important consequences for understanding mechanisms in olfactory information encoding. High-resolution functional MRI (fMRI) data from the rat olfactory bulb are presented using the blood oxygenation level dependent (BOLD) method at 7 T. Either individual or clusters of fMRI voxels suggestive of activity in the olfactory nerve and glomerular layers were reproducibly detected with repeated 2-min exposures of iso-amyl acetate at spatial resolution of 0.001-0.003 microL. The importance of glomerular clustering for olfaction and the implications of BOLD mapping with even higher spatial resolution (i.e., <<0.001 microL voxels) are discussed. High-resolution in vivo mapping of the rat olfactory bulb with fMRI at high magnetic field promises to provide novel data for understanding olfaction.

Animals↗

PubMed2006

Quantitative MRI for the assessment of bone structure and function.

Osteoporosis is the most common degenerative disease in the elderly. It is characterized by low bone mass and structural deterioration of bone tissue, leading to morbidity and increased fracture risk in the hip, spine and wrist-all sites of predominantly trabecular bone. Bone densitometry, currently the standard methodology for diagnosis and treatment monitoring, has significant limitations in that it cannot provide information on the structural manifestations of the disease. Recent advances in imaging, in particular MRI, can now provide detailed insight into the architectural consequences of disease progression and regression in response to treatment. The focus of this review is on the emerging methodology of quantitative MRI for the assessment of structure and function of trabecular bone. During the past 10 years, various approaches have been explored for obtaining image-based quantitative information on trabecular architecture. Indirect methods that do not require resolution on the scale of individual trabeculae and therefore can be practiced at any skeletal location, make use of the induced magnetic fields in the intertrabecular space. These fields, which have their origin in the greater diamagnetism of bone relative to surrounding marrow, can be measured in various ways, most typically in the form of R2', the recoverable component of the total transverse relaxation rate. Alternatively, the trabecular network can be quantified by high-resolution MRI (micro-MRI), which requires resolution adequate to at least partially resolve individual trabeculae. Micro-MRI-based structure analysis is therefore technically demanding in terms of image acquisition and algorithms needed to extract the structural information under conditions of limited signal-to-noise ratio and resolution. Other requirements that must be met include motion correction and image registration, both critical for achieving the reproducibility needed in repeat studies. Key clinical applications targeted involve fracture risk prediction and evaluation of the effect of therapeutic intervention.

Animals↗

PubMed1985

Discriminant parameters representing cerebral cortical function during anoxic anoxia investigations.

In order to quantify the effect of specific drugs on the cerebral cortex an "in vivo" model has been developed for the induction and the observation of anoxic anoxia. Rabbits are used as test animals. Sensors for the assessment of local parameters are chronically implanted: ECoG electrodes are applied; pO2 electrodes are inserted into the cortical tissue. The derived somatosensory evoked potentials are used for evaluating the cerebral cortical function. Animals are cannulated with a tracheal tube, curarized and artificially ventilated. Anoxic anoxia, controlled by a special purpose microprocessor system, may then be induced and repeated in a reproducible way. During the experiments local (pO2, ECoG, SEP) as well as general parameters (ECG, heart rate, systemic blood pressure, rectal temperature) are recorded and stored on analog magnetic tape as well as digitized with the microprocessor system. The cortical pO2 is measured with a polarographic method, the SEP's are obtained on-line by time coherent averaging and the ECoG states (e.g. epilepsy during anoxia) are derived by using band-pass filters and rms detectors. Off-line the signals (pO2, heart rate, mean systemic blood pressure, temperature) are standardized and represented together with parameters derived from ECoG and SEP. SEP-waveform parameters indicating intensity (norm) and similarity with a reference SEP signal (correlation value) are used. The measuring and processing method is still being optimized; special attention is being paid towards the quality of the calculated SEP's which are to be used for the quantification of the cortical function during reference, anoxia and recovery period. As such, in order to improve the signal-to-noise ratio of the SEP's and, consequently, of the derived parameters, ECoG signals are digitized off-line and subjected to a preprocessing, implying filtering and spectral analysis procedures.

Animals↗

PubMed2002

Determination of total tin in canned food using inductively coupled plasma atomic emission spectroscopy.

Tin is considered to be a priority contaminant by the Codex Alimentarius Commission. Tin can enter foods either from natural sources, environmental pollution, packaging material or pesticides. Higher concentrations are found in processed food and canned foods. Dissolution of the tinplate depends on the of food matrix, acidity, presence of oxidising reagents (anthocyanin, nitrate, iron and copper) presence of air (oxygen) in the headspace, time and storage temperature. To reduce corrosion and dissolution of tin, nowadays cans are usually lacquered, which gives a marked reduction of tin migration into the food product. Due to the lack of modern validated published methods for food products, an ICP-AES (Inductively coupled plasma-atomic emission spectroscopy) method has been developed and evaluated. This technique is available in many laboratories in the food industry and is more sensitive than atomic absorption. Conditions of sample preparation and spectroscopic parameters for tin measurement by axial ICP-AES were investigated for their ruggedness. Two methods of preparation involving high-pressure ashing or microwave digestion in volumetric flasks were evaluated. They gave complete recovery of tin with similar accuracy and precision. Recoveries of tin from spiked products with two levels of tin were in the range 99+/-5%. Robust relative repeatabilities and intermediate reproducibilities were <5% for different food matrices containing >30 mg/kg of tin. Internal standard correction (indium or strontium) did not improve the method performance. Three emission lines for tin were tested (189.927, 283.998 and 235.485 nm) but only 189.927 nm was found to be robust enough with respect to interferences, especially at low tin concentrations. The LOQ (limit of quantification) was around 0.8 mg/kg at 189.927 nm. A survey of tin content in a range of canned foods is given.

Food Contamination↗

PubMed2004

Determination of serum cortisol using isotope dilution-liquid chromatography-mass spectrometry as a candidate reference method.

We propose isotope-dilution mass spectrometry as a candidate reference method for determination of serum cortisol. The method uses liquid chromatography-mass spectrometry (LC-MS), interfaced with electrospray ionization, and selective monitoring of the [M + H]+ ions of cortisol and isotopically labeled cortisol. The isotope-dilution-liquid chromatography-mass spectrometry (ID-LC-MS) method simplifies sample-preparation, because samples are processed by simple solvent extraction without further clean-up and derivatization. We studied the time required for complete equilibration of endogenous cortisol and labeled cortisol spiked into serum and found it to be less than 1 h. The repeatability and the reproducibility of the method were evaluated and found to be 0.55% of the measurement value. CRM 192 and 193 from the Bureau Communautaire de Reference were analyzed for verification of the method. The results obtained from the ID-LC-MS method agreed with the certified values. The relative uncertainty of measurement results for samples in the range of a few tens of micrograms per kilogram to several hundred micrograms per kilogram was evaluated and found to be 0.56%. Immunoassay carried out by three independent clinical laboratories produced results more than 15% higher than this ID-LC-MS method, suggesting the presence of bias in the immunoassay methods.

Gas Chromatography-Mass Spectrometry↗

PubMed2006

Mediator-free amperometric determination of glucose based on direct electron transfer between glucose oxidase and an oxidized boron-doped diamond electrode.

A mediator-free glucose biosensor, termed a "third-generation biosensor," was fabricated by immobilizing glucose oxidase (GOD) directly onto an oxidized boron-doped diamond (BDD) electrode. The surface of the oxidized BDD electrode possesses carboxyl groups (as shown by Raman spectra) which covalently cross-link with GOD through glutaraldehyde. Glucose was determined in the absence of a mediator used to transfer electrons between the electrode and enzyme. O2 has no effect on the electron transfer. The effects of experimental variables (applied potential, pH and cross-link time) were investigated in order to optimize the analytical performance of the amperometric detection method. The resulting biosensor exhibited fast amperometric response (less than 5 s) to glucose. The biosensor provided a linear response to glucose over the range 6.67x10(-5) to 2x10(-3) mol/L, with a detection limit of 2.31x10(-5) mol/L. The lifetime, reproducibility and measurement repeatability were evaluated and satisfactory results were obtained.

Biosensing Techniques↗

PubMed2003

Improved method for the intracerebral engraftment of tumour cells and intratumoural treatment using a guide screw system in mice.

BACKGROUND: Orthotopic in vivo models for the experimental treatment of malignant gliomas have become indispensable to evaluate the efficacy of novel therapeutic regimens. Recently, a guide screw system was introduced which is implanted into the cranium of small rodents where it facilitates fast, repeated and exactly reproducible intracerebral injections, avoiding time consuming stereotactic procedures. Here we report our experience with this system, and describe several modifications which we introduced to improve its reliability and to simplify its application. FINDINGS: The most important modification made was the optimization of the guide screw implantation site, which needs to be adapted to the age of the mice. Other improvements were the fixation of the guide screw to the cranium of the mice using a two component adhesive. This avoids the tendency, when daily intratumoural injections are performed over several weeks, for the screw to loosen, making precise injections impossible. The injection procedure, initially described as a free-hand approach, was improved by mounting the syringe to a Greenberg retractor. This provided additional stability and speeded up the process. Applying this modified technique, we were able to achieve reproducible results with regard to engraftment rate, tumour growth, and intratumoural treatment in immunocompromized mice. INTERPRETATION: We introduced several major and some minor improvements to make working with the guide screw system more reliable, faster and more comfortable. Daily injections over a period of three weeks using this system are feasible and well tolerated by mice.

Animals↗

PubMed2005

Echocardiography induced tachycardia in a patient with a minute ventilation rate responsive pacemaker.

We report a case of a 57 year-old man with a minute ventilation rate-response pacemaker and an inappropriate increase in his heart rate during a transthoracic echocardiography study. The increase in heart rate was due to interference between echocardiography and minute ventilation sensor. This was confirmed by a repeat echocardiogram, which reproduced the same effect and turning off the minute ventilation sensor stopped the tachycardia. We suggest that deactivating the minute ventilation sensor would avoid this interaction and electrophysiologists should be aware of this unusual electromagnetic interference phenomenon.

Echocardiography↗

PubMed2006

Validation of an HPLC analytical method coupled to a multifunctional clean-up column for the determination of deoxynivalenol.

To evaluate a method using a multifunctional clean-up column coupled with high performance liquid chromatography as an official analytical method for the determination of deoxynivalenol in wheat used as food or feed, an inter-laboratory study was performed in 12 laboratories using four naturally contaminated wheat samples and one spiked sample. The relative standard deviations for repeatability (RSDr) and reproducibility (RSDR) of naturally contaminated wheat were in the range 5.8-11.3% and 12.0-20.7%, respectively. The HORRAT was less than 1.0 in each sample. From the spiking test, the recovery rate, RSDr, RSDR and HORRAT value were 100.0%, 11.2%, 10.3% and 0.5, respectively. The limit of quantification is 0.10 mg/kg from the range obtained in a linear calibration. Thus, it should be useful as a sensitive and validated analytical method for the determination of deoxynivalenol in wheat intended for use in food and feed.

Chromatography, High Pressure Liquid↗

PubMed1993

Early prediction of individual outcome after cardiopulmonary resuscitation.

Prediction of individual outcome after cardiopulmonary resuscitation is of major medical, ethical, and socioeconomic interest but uncertain. We studied the early predictive potency of evoked potential recording after cardiac arrest in 66 resuscitated patients who returned to spontaneous circulation but were unconscious and mechanically ventilated. Detailed long-latency and short-latency sensory evoked potentials were recorded and neurological evaluations were done 4-48 h after admission to intensive care. In all 17 patients with favourable outcome (cerebral performance categories 1 and 2) the cortical evoked potential N70 peak, a reliable measure of cortical function, was detected between 74 and 116 ms. In 49 patients with bad outcome (categories 4 and 5) the N70 peak was absent in 35 or found with a delay between 121 and 171 ms in 14 (p < 0.05 vs favourable outcome). Thus the predictive ability was 100% with cutoff of 118 ms. To confirm reproducibility and validity, repeated tracings, and linked-earlobe referenced techniques were done and gave similar results. Early recording of long-latency evoked potentials after cardiopulmonary resuscitation is highly predictive of outcome.

Adolescent↗

PubMed1992

Mechanism of hypotension following rapid infusion of protamine sulfate in anesthetized dogs.

Protamine sulfate (PS), used to neutralize the anticoagulant effect of heparin, is often associated with systemic hypotension. Whether this hypotension is secondary to a depression of myocardial function is not clear. The present study tested the hypothesis that systemic hypotension was accompanied by a depression in myocardial function and examined the possible role of histamine in mediating the cardiovascular response to PS. Seven conditioned dogs were chronically instrumented with pressure and ultrasonic dimension transducers. Studies were conducted under halothane anesthesia 7 to 10 days after instrumentation. Cardiac contractility was assessed using the slope, Ees, of the linear regression of the left ventricular end-systolic pressure-diameter relationship. Intravenous infusion of PS, 5 mg/kg, when given in periods of less than 30 seconds, decreased systemic arterial pressure by 45% (from 101 +/- to 54 +/- 5 mm Hg) without change in heart rate. Cardiac output decreased by 22% from control and the slope Ees decreased by 37% (from 14.5 +/- 1.2 to 8.7 +/- 1.4 mm Hg/mm). Systemic vascular resistance decreased by 34% (from 2581 +/- 121 to 1712 +/- 200 dyne.s.cm-5). The cardiovascular depression caused by PS was transient and could not be reproduced by a repeated dose given within a 60-minute period. Antagonists of histamine (diphenhydramine and cimetidine) could not attenuate the PS-induced cardiovascular depression. This depression was independent of preheparinization and did not occur when PS was infused slowly over a 2-minute period. The data clearly demonstrate negative inotropic and vasodilator effects of PS following rapid administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗

PubMed2006

Precision determination for the specific oxygen uptake rate (SOUR) method used for biological stability evaluation of compost and biostabilized products.

This work represents the first attempt to evaluate the precision of the specific oxygen uptake rate method expressed in terms of repeatability (r) and reproducibility limits (R). Three laboratories were involved in an inter-laboratory test for the validation of respiration analyses on six biomass samples (three composts and three biostabilized products) having different degrees of biological stability. Both the maximum specific oxygen uptake rate peak (SOUR) and the cumulative oxygen demand after 12 h (OD(12)) and 20 h (OD(20)) of respiration test were investigated. Precisions expressed as the relative standard deviation were in the range of 9-41%. Linear regressions found for r and R, versus OD(12) and OD(20), enabled derivation of precision values (r and R) for all respirometric levels within the operating range. The OD(12) and OD(20) indices were found to be more adequate to indicate biological stability since they were less influenced by random errors than the SOUR index.

Oxygen↗

PubMed2004

Short-term BOD (BODst) as a parameter for on-line monitoring of biological treatment process. Part I. A novel design of BOD biosensor for easy renewal of bio-receptor.

A novel design of a biochemical oxygen demand (BOD) biosensor has been developed for on-line monitoring of easily biodegradable organic compounds in aqueous samples. The biological recognition element of the sensor could be easily renewed by injecting new bacterial paste without disassembling the sensor system. The sensor measurements were carried out in the initial-rate mode using a flow injection (FI) system, resulting in 60 s for one sample analysis followed by a recovery time less than 10 min. The sensor performance achieved showed a wide detection linearity over the range of 5-700 mg BOD5.l(-1) and a generally good agreement between the BOD values estimated by the biosensor and the conventional 5-day test. Furthermore, the precision test was in the control range (i.e. repeatability < or = /+/-7.5%/, reproducibility < or = /+/-7.3%/). The sensor could be used over 1 week in continuous test, however, the best performance was found within the first 24 h where standard deviation of the sensor response was +/-2.4%. The design of the sensor allows easy and fast renewal of the cells used as sensing elements. Replacement of biological recognition element and calibration of the sensor responses can be performed in a rather simple procedure on a daily regular basis. By using a mixed culture as the bio-receptor, one gets a sensor that reacts to a wide range of substrates. The new sensor construction will thus allow fast and convenient replacement of the bio-receptor and on-line assay of a broad range of substrates. This makes the sensor being an interesting and promising candidate for on-line monitoring of biological treatment process.

Bacteria, Aerobic↗

PubMed2004

Trace level determination of acrylamide in cereal-based foods by gas chromatography-mass spectrometry.

A quantitative method has been developed for the determination of trace levels (<50 microg/kg) of acrylamide in cereal-based foods. The method is based on extraction of acrylamide with water, acidification and purification with Carrez I and II solutions, followed by bromination of the acrylamide double bond. The reaction product (2,3-dibromopropionamide) is extracted with ethyl acetate/hexane (4:1, v/v), dried over sodium sulfate, and cleaned up through a Florisil column. The derivative is then converted to 2-bromopropenamide by dehydrobromination with triethylamine and analyzed by gas chromatography coupled to mass spectrometry (GC-MS), employing (13C3)acrylamide as internal standard. In-house validation data for commercial and experimental cereal products showed good precision of the method, with repeatability and intermediate reproducibility relative standard deviations below 10%. The limit of detection and limit of quantitation are estimated at 2 and 5 microg/kg, respectively, and recoveries of acrylamide from samples spiked at levels of 5-500 microg/kg ranged between 93 and 104% after correction of analyte loss by the internal standard. Finally, a comparative test organized with two independent laboratories provided additional confidence in the good performance of the method, particularly at very low concentration levels.

Acrylamide↗

PubMed2006

Preparation and improvement of release behavior of chitosan microspheres containing insulin.

Chitosan microsphere has potential applications in orally and other mucosally administration of protein and peptide drug, because it shows excellent mucoadhesive and permeation enhancing effect across the biological surfaces. The control of the size and size distribution of chitosan microsphere is necessary in order to improve its reproducibility, bioavailability and repeatable release behavior. Furthermore, it is a big challenge how to maintain the chemical stability of protein drug and improve its release behavior in the preparation of chitosan microspheres, because conventional crosslinking method by glutaraldehyde cannot be used in encapsulation of protein drug containing amino group. In this study, we established a method to prepare uniform-sized microsphere, and solve above problems by combining a special membrane emulsification technique and a step-wise crosslinking method. The preparative condition was optimized, and the chemical stability of protein, encapsulation efficiency, and release behavior were compared with conventional preparative method of drug-loaded chitosan microspheres. As a result, fairly uniform chitosan microspheres were obtained with a coefficient of variation (C.V.) value less than 11%, and the step-wise crosslinking method developed specially for membrane emulsification method provided the microspheres with higher encapsulation efficiency (80%), higher chemical stability of insulin (>95%), lower burst release and steady release behavior.

Chemistry, Pharmaceutical↗

PubMed2004

Development and validation of a LC-method for determination of catechin and epicatechin in aqueous extractives from leaves of Maytenus ilicifolia.

A reverse phase-LC method was developed and validated for separation and quantification of catechin and epicatechin in aqueous extractives from leaves of Maytenus ilicifolia. The analysis was performed using a C(18) column with acetic acid-acetonitrile gradient elution. The detection was carried out by UV at 280 nm and the peak identification was based on the retention times and by co-chromatography with reference substances. High coefficients of determination were achieved for both catechin and epicatechin peaks from the standard solutions (0.9996 and 0.9999), as well as from extractives (0.9981 and 0.9982, respectively). The method showed good repeatability (R.S.D. <1.5%), reproducibility (R.S.D. <5%) and good accuracy for both catechin and epicatechin peaks (101.4%, R.S.D. = 1.18% and 100.6%, R.S.D. = 2.07%, respectively).

Catechin↗

PubMed2005

Determination of dipyridamole in pharmaceutical preparations using square wave voltammetry.

An analytical methodology using square wave voltammetry (SWV) at a hanging mercury drop electrode (HMDE) was developed for the quantitative determination of dipyridamole (DIP), a drug used for the treatment of several cardiovascular diseases, in pharmaceutical tablets and injections of Persantin in phosphate buffer (pH 3.0; 0.1M). After optimization of the parameters for SWV, analytical curves were obtained for application in the range of 1.28 x 10(-6)M to 7.02 x 10(-6)M. It was found a detection limit (DL) of 1.88 x 10(-8)M (9.50 ng/ml). The repeatability and the reproducibility of the method were determinated by successive measurements of DIP solutions on the range of the analytical curve with a coefficient variation of 0.97% (n=5) and 1.15%, respectively. The apparent recoveries were obtained by the IUPAC recommended procedure using the second reduction peak. Recoveries obtained by SWV were compared with the UV-vis spectrophotometric method. It was found that the determination of DIP in Persantin tablets gave a mean value of 75.6+/-0.4 mg (100.8%) and 68.9+/-0.3 mg (91.8%) for SWV and UV-vis spectrophotometry, respectively. In the case of injections, it was found 10.4+/-0.1 mg (103.4%) and 9.9+/-0.2 mg (99.9%) for SWV and UV-vis spectrophotometry. Both apparent recoveries for the two types of formulations are in good accordance with the declared value of 75 mg (tablets) and 10 mg (injections).

Chemistry, Pharmaceutical↗