Weighted calibration
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A comparison of the s- and w-detections of molecular weight, a necessary condition for precise determination of interdetector volume in size exclusion chromatography of polymers with the dual light scattering--concentration detection, is examined. From the theoretical analysis for a polymer with the log-normal molecular weight distribution it follows that the error in determination of the local calibration, i.e., of a logarithmic dependence of molecular weight on elution volume obtained by the s-detection, from the known dependence of radius of gyration on elution volume and of molecular weight on the radius of gyration, remains linear and is slightly shifted with respect to that obtained by the w-detection (dual detection giving the weight-average molecular weight) towards higher molecular weights, the difference being below the experimental error. It also follows that the error in the slope of local calibration found by the w-detection is given by the ratio of the error in interdetector volume and the variance of the elution curve. This is demonstrated on several polymer samples with symmetric elution curves of polymer samples differing in polydispersity indices. The range of this rule depends on the broadness and symmetry of elution curves. The precision of the interdetector volume determination depends therefore strongly on the Mw/Mn ratio of the sample.
In situ extraction of steroid hormones from waste water using adsorption-based integrative passive samplers represents a promising approach for their monitoring in water at ultra-trace concentrations. Three passive samplers, namely a POCIS, a Chemcatcher fitted with an Empore SDB-RPS disk, and an Empore SDB-RPS disk-based sampler with enhanced water flow, were calibrated in situ in treated municipal wastewater for the purpose of monitoring five estrogens (17-β-estradiol, 17-α-estradiol, 17-α-ethinylestradiol, estrone and estriol) at sub ng per litre concentrations. Uptake of steroids to samplers during 14-day exposure in wastewater was compared with steroid concentrations in daily collected composite water samples. Sampling rates were obtained from a numerical solution of first order uptake kinetics equations describing the uptake of compounds into a passive sampler over time. Mass transfer of steroids in the Chemcatcher fitted with naked Empore disks was more than two times faster than in the POCIS sampler. The uptake capacity of the applied Empore disk was not sufficient for integrative uptake of all tested steroids during the entire 14-day exposure. Time-weighted average concentrations of steroids estimated at concentrations in units of ngL-1using the in situ-calibrated samplers were within a factor of two from values obtained using composite water samples.
A passive sampler based on stir bars coated with polydimethylsiloxane (PDMS) was calibrated for the measurement of time-weighted average concentrations of hydrophobic micropollutants, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls and organochlorine pesticides, in water. Stir bar/water partition coefficients were measured by equilibrating bars with sheets made of silicone rubber material for which partition coefficients had been reported previously. Kinetic parameters characterising the exchange of analytes between stir bars and water were determined under controlled exposure conditions using a passive dosing system. The dosing system consisted of silicone rubber sheets with a large surface area, spiked with analytes. During stir bar sampler exposure, analytes partitioned from dosing sheets to water in the exposure tank and maintained constant exposure concentrations. Reversible and isotropic exchange kinetics of analytes between sampler and water was confirmed by measuring the release of a range of performance reference compounds (PRCs) from stir bars. Application of a two-resistance model confirmed that, except for hexachlorocyclohexane isomers, uptake of the test compounds under the experimental conditions was controlled by diffusion in the water boundary layer. This permits the application of PRCs for in situ calibration of uptake kinetics of test compounds to stir bars.
- MeSH
- chemická frakcionace metody MeSH
- chemické látky znečišťující vodu analýza chemie izolace a purifikace MeSH
- hydrofobní a hydrofilní interakce * MeSH
- kalibrace MeSH
- kinetika MeSH
- organické látky analýza chemie izolace a purifikace MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
A tutorial and spreadsheet for the validation and bottom-up uncertainty evaluation of quantifications performed by instrumental methods of analysis based on linear weighted calibrations is presented. The developed tool automatically assesses if calibrator values uncertainty is negligible given instrumental signal precision, assesses signal homoscedasticity by the Levene's test, guides the selection of weighting factors and evaluates the fitness of the regression model to define the calibration curve. The spreadsheet allows the use of the linear weighted regression model without the need for collecting many replicate signals of calibrators and sample by taking previously developed detailed models of signal precision variation in the calibration interval after adjustments to the daily precision conditions. This tool was successfully applied to the determination of the mass concentration of Cd, Pb, As, Hg, Co, V and Ni in a nasal spray by ICP-MS after samples dilution and acidification. The developed uncertainty models were checked through the analysis of nasal sprays after spiking with known analyte concentration levels. The metrological compatibility between estimated and reference analyte levels for 95% or 99% confidence level supports uncertainty model adequacy. The spiked samples were quantified from many replicate signals but uncertainty evaluation from duplicate calibrator and sample signals was assessed by randomly selecting calibrators and sample signals and by numerically defining a minimum acceptable success rate of the compatibility tests. The developed model was proven adequate to quantify the uncertainty of the studied measurements.
- MeSH
- kalibrace MeSH
- lineární modely MeSH
- nejistota MeSH
- nosní spreje * MeSH
- spektrální analýza MeSH
- Publikační typ
- časopisecké články MeSH
- Klíčová slova
- InBody, DSM-BIA,
- MeSH
- antropometrie * přístrojové vybavení MeSH
- kalibrace MeSH
- lidé MeSH
- složení těla * MeSH
- tělesné váhy a míry MeSH
- váhy a míry normy přístrojové vybavení MeSH
- Check Tag
- lidé MeSH
The approaches to matrix effects determination and reduction in ultra-high performance supercritical fluid chromatography with mass spectrometry detection have been evaluated in this study using different sample preparation methods and investigation of different calibration models. Five sample preparation methods, including protein precipitation, liquid-liquid extraction, supported liquid extraction, and solid phase extraction based on both "bind and elute" and "interferent removal" modes, were optimized with an emphasis on the matrix effects and recovery of 8 forms of vitamin E, including α-, β-, γ-, and δ-tocopherols and tocotrienols, from plasma. The matrix effect evaluation included the use and comparison of external and internal calibration using three models, i.e., least square with no transformation and no weighting (1/x0), with 1/x2 weighting, and with logarithmic transformation. The calibration model with logarithmic transformation provided the lowest %-errors and the best fits. Moreover, the type of the calibration model significantly affected not only the fit of the data but also the matrix effects when evaluating them based on the comparison of calibration curve slopes. Indeed, based on the used calibration model, the matrix effects calculated from calibration slopes ranged from +92% to - 72% for α-tocopherol and from -77% to +19% in the case of δ-tocotrienol. Thus, it was crucial to calculate the matrix effect by Matuszewski's post-extraction approach at six concentration levels. Indeed, a strong concentration dependence was observed for all optimized sample preparation methods, even if the stable isotopically labelled internal standards (SIL-IS) were used for compensation. The significant differences between individual concentration levels and compounds were observed, even when the tested calibration range covered only one order of magnitude. In methods with wider calibration ranges, the inappropriate use of calibration slope comparison instead of the post-extraction addition approach could result in false negative results of matrix effects. In the selected example of vitamin E, solid-phase extraction was the least affected by matrix effects when used in interferent removal mode, but supported liquid extraction resulted in the highest recoveries. We showed that the calibration model, the use of a SIL-IS, and the analyte concentration level played a crucial role in the matrix effects. Moreover, the matrix effects can significantly differ for compounds with similar physicochemical properties and close retention times. Thus, in all bioanalytical applications, where different analytes are typically determined in one analytical run, it is necessary to carefully select the data processing in addition to the method for the sample preparation, SIL-IS, and chromatography.
- MeSH
- extrakce na pevné fázi metody MeSH
- hmotnostní spektrometrie * metody MeSH
- kalibrace MeSH
- lidé MeSH
- superkritická fluidní chromatografie * metody MeSH
- vitamin E * krev analýza MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
In the present study, we have evaluated the effectiveness of a passive sampler for polar organic chemicals to accumulate a group of widespread and hazardous tumor-promoting toxins produced in cyanobacterial water blooms-microcystins (MC). The previously optimized configuration of the sampler based on polycarbonate membrane and Oasis HLB sorbent (2.75 mg/cm(2)) was validated under various exposure scenarios in laboratory and field. Calibration of the passive sampler conducted under variable conditions and concentrations of MC revealed linearity of the sampling up to 4 weeks. The sampling rates of microcystins for two different exposure scenarios were derived (e.g., MC-LR: R (s) = 0.017 L/day under static and 0.087 L/d under turbulent conditions). R (s) values were further used for calculations of time-weighted average concentrations in natural water. Improved sensitivity and selectivity of the in-house-made sampler was observed in comparison with the commercially available Polar Organic Compound Integrative Sampler (POCIS). Comparisons of grab and passive sampling methods were performed during cyanobacterial water bloom season in the Brno reservoir, Czech Republic in 2008. Data obtained by passive sampling provided a more relevant picture of the situation and enabled better assessment of potential risks. The present study demonstrated that the modification of POCIS is suitable for monitoring of occurrence and retrospective estimations of microcystin water concentrations, especially with respect to the control of drinking water quality.
- MeSH
- bakteriální toxiny izolace a purifikace MeSH
- kalibrace MeSH
- membrány umělé MeSH
- mikrocystiny izolace a purifikace MeSH
- monitorování životního prostředí přístrojové vybavení MeSH
- mořské toxiny izolace a purifikace MeSH
- sinice chemie MeSH
- Publikační typ
- časopisecké články MeSH
- hodnotící studie MeSH
- práce podpořená grantem MeSH
The knowledge of the dynamic extremes of human voice is important for voice diagnostics and for scientific purposes. Numerous authors have published on the dynamic range of human voice but the methodology has been quite heterogenous and the exact values of the dynamic extremes are often unclear. There has been a need for a carefully documented study about measuring extreme limits of normal voice with easily reproducible methodology. We measured 37 subjects, 23 women and 14 men for this experiment. Two microphones were used (one head-mounted and one stand-mounted), which were calibrated at a standard distance 30 cm from the mouth. The head-mounted microphone was used for measuring the softest phonations and the stand-mounted for measuring the loudest ones. The loudest level was determined from calling the Czech words “Hej, Hou, Haló” as the peak sound level. The softest level was determined as a minimum of the fast time-weighted sound level from the softest sustained phonations on vowel [a:]. The standard weighting filtres A, C or Z and a custom high-pass filter were used to decrease ambient noise. The level of the loudest phonation was found to be 127 dB at 30 cm from the mouth (male subject) and the softest phonation was found to be 31 dB (A-weighted) at 30 cm from mouth (male subject). These levels appear to be greater than those measured previously and can serve as a basis for specifying dynamic ranges of microphone intended for voice measurements.
- MeSH
- akustika řeči MeSH
- audiovizuální pomůcky využití MeSH
- experimenty na lidech MeSH
- financování organizované MeSH
- fonace fyziologie MeSH
- fonetika MeSH
- hlas fyziologie MeSH
- kalibrace MeSH
- kvalita hlasu fyziologie MeSH
- lidé MeSH
- percepce řeči MeSH
- počítačové zpracování signálu přístrojové vybavení MeSH
- statistika jako téma MeSH
- vlnková analýza MeSH
- vnímání výšky zvuku MeSH
- Check Tag
- lidé MeSH
