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Variation Coefficient (variation + coefficient)
Selected AbstractsA novel ultra-sensitive method for the quantification of glycosaminoglycan disaccharides using an automated DNA sequencerELECTROPHORESIS, Issue 7 2006Kay Vogel Abstract Analysis of glycosaminoglycans (GAGs) is of increasing importance concerning alterations in extracellular matrix composition and selectivity of glomerular basement membrane. In this report we describe the analysis of chondroitin sulfate disaccharides as an example of GAG ,disaccharide analysis using standard DNA sequencing equipment (DNA sequencer-assisted GAG disaccharide separation, DSA-GAGS). The presented methodology allows nanomolar quantification of 8-aminopyrene-1,3,6-trisulfonic acid (APTS)-derived GAG disaccharides. In comparison to RP-HPLC the established method is much more sensitive, showing detection limits of 38,fmol/,L. Variation coefficients were approximately 10%, enabling exact quantifications after run times of 17,min at 30°C and an electrophoresis voltage of 15,kV; using a capillary DNA sequencer, available in many molecular laboratories, presented advantages like automated sample injection, opportunity of high-throughput analyses, separation of even sulfated disaccharide epimers, and the possibility of using APTS-derived fucose as an internal standard. Furthermore, highly reproducible retention times rendered easy identification of specific signals (SD,0.02). With regard to these results, the described method is a useful tool for the quantification of GAG disaccharides in low amounts, indicating advantages of obverse RP-HPLC and slab gel polyacrylamide electrophoresis in sensitivity, error-proneness, automation, and handling. [source] Voltammetric Reduction of a 4-Nitroimidazole Derivative on a Multiwalled Carbon Nanotubes Modified Glassy Carbon ElectrodeELECTROANALYSIS, Issue 13 2008P. Jara-Ulloa Abstract We report the electrochemical behavior of a 4-nitroimidazole derivative, 1-methyl-4-nitro-2-hydroxymethylimidazole (4-NImMeOH), on glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT). As dispersing agents, dimethylformamide (DMF) and water were used. The electrochemical response of the resulting electrodes was evaluated using linear sweep, cyclic and square-wave voltammetry (LSV, CV and SWV). Several parameters such as medium pH, nature and concentration of the CNTs dispersion and accumulation time were tested. The optimal conditions determined for obtain better response were: pH,2, dispersion concentration=4,mg/mL of CNT in water, accumulation time=7,min. The MWCNT-modified GCE exhibited attractive electrochemical properties producing enhanced currents with a significant reduction in the overpotential and good signal-to-noise characteristics, in comparison with the bare GCE. The modified electrode is highly repeatable for consecutive measurements, reaching a variation coefficient of 2.9% for ten consecutive runs. [source] Adapted DAX-8 fractionation method for dissolved organic matter (DOM) from soils: development, calibration with test components and application to contrasting soil solutionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2009F. Amery Summary Most methods to fractionate natural dissolved organic matter (DOM) rely on sorption of acidified DOM samples onto XAD-8 or DAX-8 resin. Procedural differences among methods are large and their interpretation is limited because there is a lack of calibration with DOM model molecules. An automated column-based DOM fractionation method was set up for 10-ml DOM samples, dividing DOM into hydrophilic (HPI), hydrophobic acid (HPOA) and hydrophobic neutral (HPON) fractions. Fifteen DOM model components were tested in isolation and in combination. Three reference DOM samples of the International Humic Substances Society were included to facilitate comparison with other methods. Aliphatic low-molecular-weight acids (LMWAs) and carbohydrates were classified as HPI DOM, but some LMWAs showed also a partial HPO character. Aromatic LMWAs and polyphenols partitioned in the HPOA fraction, menadione (quinone) and geraniol (terpenoid) in HPON DOM. Molecules with log Kow > 0.5 had negligible HPI fractions. The HPO molecules except geraniol had specific UV absorbance (SUVA, measure for aromaticity) >3 litres g,1 cm,1 while HPI molecules had SUVA values <3 litres g,1 cm,1. Distributions of DOM from eight soils ranged from 31 to 72% HPI, 25 to 46% HPOA and 2 to 28% HPON of total dissolved organic carbon. The SUVA of the HPI DOM was consistently smaller compared with the HPOA DOM. The SUVA of the natural DOM samples was not explained statistically by fractionation and the variation coefficient of SUVA among samples was not reduced by fractionation. Hence, fractionation did not reduce the variability in this DOM property, which casts some doubts on the practical role of DOM fractionation in predicting DOM properties. [source] Extreme body size variability in the golden silk spider (Nephila edulis) does not extend to genitaliaJOURNAL OF ZOOLOGY, Issue 1 2000Gabriele Uhl Abstract Nephila edulis is a spider with large body size variability in males and females. Genital characters show negative allometric values compared to somatic characters. In males, the embolus (the most important structure for sperm transfer) had a significantly lower coefficient of variation than body size. This suggests that male genitalia are under stabilizing selection favouring intermediate size. Female N. edulis showed a trend similar to males regarding allometric values in genitalia. In females, however, the variation coefficient in a specific genital character crucial for successful copulation did not differ from that of indicators for overall body size. This suggests that in Nephila the genitalia of the females experience less stabilizing selection than those of the males. In male and female genitalia, the mode of selection seems to cause developmental instability not in degrees of fluctuating asymmetry but in the degree of data scatter which indicates a lower coefficient of determination. [source] Individual variations of serum testosterone in patients with prostate cancer receiving androgen deprivation therapyBJU INTERNATIONAL, Issue 3 2009Juan Morote OBJECTIVE To analyse individual variations in serum testosterone level, the cumulative rate of ,breakthrough' increases over castrate levels, and to evaluate whether the increases can be predicted. PATIENTS AND METHODS Serum testosterone levels were determined every 6 months over 3 years in 73 consecutive patients with prostate cancer who were medically castrated, prospectively enrolled in a single tertiary academic centre. Patients recruited for this study were being treated with a 3-monthly depot of luteinizing hormone-releasing hormone agonist over 6,48 months. Serum testosterone was measured using a chemiluminescent assay with a lower sensitivity level of 15 ng/dL and interassay coefficient of variation of 25% at low testosterone concentrations. RESULTS Individual variations could not be explained by the interassay variation coefficient in 26% of the patients. The rate of breakthrough increases >50 ng/dL increased from 12.3% at the first determination to 24.7% at the third, then remaining stable. The rate of breakthrough increases of 20,50 ng/dL increased from 27.4% at the first determination to 31.5% at the second, and then remained stable. A first determination of <20 ng/dL provided an 11.4% probability for future increases of >50 ng/dL, with a 5.7% probability if two consecutive determinations were <20 ng/dL and a null probability when three consecutive determinations were <20 ng/dL. CONCLUSIONS Individual variations in serum testosterone level cannot be explained by the coefficient of variation of the assay in a quarter of patients who are medically castrated. Breakthrough increases over castrate levels increase over time and those of >50 ng/dL can be predicted from the previous levels. [source] Measurement of gp210 autoantibodies in sera of patients with primary biliary cirrhosisJOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 4 2007Alicja Bauer Abstract Primary biliary cirrhosis (PBC) is an autoimmune liver disease with unknown etiology. Patients with PBC have antimitochondrial autoantibodies (AMA) and additionally 50% of them have antinuclear antibodies (ANA). A 15,amino acid fragment (DRKASPPSGLWSPAY) from the C-terminal part of the nuclear envelope glycoprotein gp210 has been proposed as one of the antigenic targets for ANA. The aim of this work was to develop an immunoenzymatic assay for determination of gp210 autoantibodies using for its binding a synthetic pentadecapeptide derived from the gp210 amino acid sequence and to determine level of these autoantibodies in sera of patients with PBC and other autoimmune liver diseases from Poland. Polystyrene microtitration plates coated with the synthetic peptide were consecutively incubated with diluted sera, anti-human immunoglobulin G (IgG) antibodies conjugated with horseradish peroxidase, and with tetramethylobenzidine. Optical density (OD) was read at 450 nm. The mean values of the intra- and interassay of variation coefficients of the test were 4.1 and 10.2%, respectively. Anti-gp210 was detected in 44% of PBC patients and in 6% of patients with PSC. The results were negative for healthy blood donors and other controls. The specificity of the test was 99%, so the anti-gp-210 autoantibodies estimated on DRKASPPSGLWSPAY can be a reliable marker of PBC. J. Clin. Lab. Anal. 21:227,231, 2007. © 2007 Wiley-Liss, Inc. [source] Optimization of solid-phase microextraction methods for GC-MS determination of terpenes in wineJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2005Rosa M Peña Abstract Solid-phase microextraction using a 100 µm poly(dimethylsiloxane) fiber, followed by gas chromatography,mass spectrometry determination, has been optimized for the analysis of some terpenes in wine samples. The best results were obtained by direct immersion of the fiber using a sampling period of 15 min with constant magnetic stirring (1100 rpm) and an extraction temperature of 20 °C. The sample volume was 7 ml with 25% NaCl, in a 15 ml capped vial. Desorption was performed directly in the gas chromatograph injector port over 5 min at 250 °C using the splitless mode. The method is sensitive, with detection limits between 11 and 25 µg l,1, precise, with variation coefficients in the range 1.28,3.71%, and linear over more than one order of magnitude. The related conditions were used for wine sample analyses with recoveries between 71.8 and 90.9%. Solid-phase microextraction remains an attractive alternative technique due to its rapidity and because it is a solvent-free extraction. Copyright © 2005 Society of Chemical Industry [source] Forearm blood flow measurements using computerized R-wave triggered strain-gauge venous occlusion plethysmography: unilateral vs. bilateral measurementsCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2001Adriaan M. Kamper The human forearm is a well established model to study local vascular reactivity in humans in vivo, using strain-gauge venous occlusion plethysmography to measure blood flow and changes in blood flow in the forearm. To reduce the intra-individual variability of the forearm blood flow (FBF), it has been advocated that simultaneous measurements of contralateral forearm blood flow is obligatory. Therefore, the use of the calculated forearm ratio (FR) is recommended instead of using the actual FBF. In the present study we compared the intra-individual variability of forearm blood flow measurements and the forearm ratio, by using computerized R-wave triggered strain-gauge venous occlusion plethysmography, to test if bilateral expression of measurements is better than unilateral. Results were obtained in eight volunteers. Intra-arterial infused sodium nitroprusside induced a dose dependent increase in forearm blood flow and a dose dependent increase in the calculated forearm ratio. Intra-arterial infused norepinephrine induced a dose dependent decrease in forearm blood flow and a dose dependent decrease in the calculated forearm ratio. The differences between the variation coefficients of the forearm blood flow measurements and the calculated forearm ratio were different. These results support our hypothesis that by using a computerized, R-wave triggered system for unilateral forearm blood flow measurement is a more reliable outcome than the calculated forearm ratio derived from bilateral measurements. [source] | ||||||||||||||||