Showing papers on "Calibration curve published in 2007"

Appropriate calibration curve fitting in ligand binding assays.

Abstract: Calibration curves for ligand binding assays are generally characterized by a nonlinear relationship between the mean response and the analyte concentration. Typically, the response exhibits a sigmoidal relationship with concentration. The currently accepted reference model for these calibration curves is the 4-parameter logistic (4-PL) model, which optimizes accuracy and precision over the maximum usable calibration range. Incorporation of weighting into the model requires additional effort but generally results in improved calibration curve performance. For calibration curves with some asymmetry, introduction of a fifth parameter (5-PL) may further improve the goodness of fit of the experimental data to the algorithm. Alternative models should be used with caution and with knowledge of the accuracy and precision performance of the model across the entire calibration range, but particularly at upper and lower analyte concentration areas, where the 4-and 5-PL algorithms generally outperform alternative models. Several assay design parameters, such as placement of calibrator concentrations across the selected range and assay layout on multiwell plates, should be considered, to enable optimal application of the 4- or 5-PL model. The fit of the experimental data to the model should be evaluated by assessment of agreement of nominal and model-predicted data for calibrators.

Laboratory and Ambient Particle Density Determinations using Light Scattering in Conjunction with Aerosol Mass Spectrometry

Abstract: A light scattering module has been integrated into the current AMS instrument. This module provides the simultaneous measurement of vacuum aerodynamic diameter (d va) and scattered light intensity (RLS) for all particles sampled by the AMS above ∼180 nm geometric diameter. Particle counting statistics and correlated chemical ion signal intensities are obtained for every particle that scatters light. A single calibration curve converts RLS to an optical diameter (d o). Using the relationship between d va and d o the LS-AMS provides a real-time, per particle measurement of the density of the sampled aerosol particles. The current article is focused on LS-AMS measurements of spherical, non-absorbing aerosol particles. The laboratory characterization of LS-AMS shows that a single calibration curve yields the material density of spherical particles with real refractive indices (n) over a range from 1.41 < n < 1.60 with an accuracy of about ±10%. The density resolution of the current LS-AMS system is also shown...

Systems and methods for acquiring calibration data usable in a pulse oximeter

Abstract: The present disclosure includes a pulse oximeter attachment having an accessible memory. In one embodiment, the pulse oximeter attachment stores calibration data, such as, for example, calibration data associated with a type of a sensor, a calibration curve, or the like. The calibration data is used to calculate physiological parameters of pulsing blood.

A statistical overview on univariate calibration, inverse regression, and detection limits: Application to gas chromatography/mass spectrometry technique

Abstract: The paper summarizes critically the current approaches for the calculation of the limits of detection and quantification. In the context of the description of the method based on the calibration line, the arguments concerning the underlying experimental design, the choice of the appropriate model in the univariate regression, the effects of the dispersion characteristics of the data are deeply discussed. The effects of the scedasticity of the experimental data are taken into account in the obtainment of the calibration curve and in its utilization. To gain transparency, adaptability, and tutorial effectiveness the explicit formulas relevant to the use of straight line and quadratic models are reported. An application of the described procedures to GC-MS data is reported as an illustrative example. © 2006 Wiley Periodicals, Inc., Mass Spec Rev 26:1–18, 2007

Method and system for dynamically updating calibration parameters for an analyte sensor

Abstract: Methods and apparatuses including determining a calibration parameter associated with a detected analyte value, calibrating the analyte value based on the calibration parameter, and dynamically updating the calibration parameter are disclosed. Also provided are systems, kits, and computer program products.

Two Methods for the Determination of Enantiomeric Excess and Concentration of a Chiral Sample with a Single Spectroscopic Measurement

Abstract: The previously established enantioselective indicator–displacement assays (eIDAs) for the determination of concentration and enantiomeric excess (ee) require two spectroscopic measurements for each chiral sample. To further simplify the operation of eIDAs, we now introduce two innovative analytical methods, both of which utilize a dual-chamber quartz cuvette, which reduces the number of spectroscopic measurements from two to one. An attractive feature of this cuvette is that the concentration- and ee-dependent absorption data can be collected at the isosbestic points or transparent regions of the spectra recorded in each individual chamber, thereby reflecting optical changes that occur in the other chamber. Therefore, two independent equations, which are needed to solve the values of the two independent variables—concentration and ee—can be established with only a single spectroscopic measurement. The first method takes advantage of this feature in conjunction with a judicious choice of indicator/host combinations to generate concentration- and ee-dependent calibration curves. Our second method removes the requirement to measure equilibrium constants and molar absorptivities altogether through the use of artificial neural networks (ANNs). The most frequently used three-layer feed-forward network is generated, which relates the absorption data to concentration and ee of the samples by training with a back propagation procedure. Here, the data collection is not limited to the isosbestic points or transparent regions. Both approaches enabled accurate and rapid determination of concentration and ee of chiral samples. The technology removes the relative difficulty, which is the need for two separate measurements for concentration and ee respectively, of analyzing chiral samples compared to achiral samples. When implemented in a high-throughput format, this technology should greatly facilitate the discovery of asymmetric catalysts in the same way as conventional high-throughput screening assays.

Spectral simulation methodology for calibration transfer of near-infrared spectra.

Abstract: A spectrum simulation method is described for use in the development and transfer of multivariate calibration models from near-infrared spectra. By use of previously measured molar absorptivities and solvent displacement factors, synthetic calibration spectra are computed using only background spectra collected with the spectrometer for which a calibration model is desired. The resulting synthetic calibration set is used with partial least squares regression to form the calibration model. This methodology is demonstrated for use in the analysis of physiological levels of glucose (1–30 mM) in an aqueous matrix containing variable levels of alanine, ascorbate, lactate, urea, and triacetin. Experimentally measured data from two different Fourier transform spectrometers with different noise levels and stabilities are used to evaluate the simulation method. With the more stable instrument (A), well-performing calibration models are obtained, producing a standard error of prediction (SEP) of 0.70 mM. With the less stable instrument (B), the calibration based solely on synthetic spectra is less successful, producing an SEP value of 1.58 mM. For cases in which the synthetic spectra do not describe enough spectral variance, an augmentation protocol is evaluated in which the synthetic calibration spectra are augmented with the spectra of a small number of experimentally measured calibration samples. For instruments A and B, respectively, augmentation with measured spectra of nine samples lowers the SEP values to 0.64 and 0.85 mM.

Preparation and characterization of calibration standards for bone density determination by micro-computed tomography

Abstract: Phantoms for the calibration of local bone mineral densities by micro-computed tomography (μCT), consisting of lithium tetraborate (Li2B4O7) with increasing concentrations of hydroxyapatite [HAp, Ca10(PO4)6(OH)2] have been prepared and characterized for homogeneity. Large-scale homogeneity and concentration of HAp in the phantom materials was determined using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), while homogeneity on the micrometer scale was assessed through μCT. A series of standards was prepared by fusion of pure HAp with Li2B4O7 in a concentration range between 0.12 and 0.74 g cm−3. Furthermore, pressed and sintered pellets of pure HAp were prepared to extend the calibration range towards densities of up to 3.05 g cm−3. A linear calibration curve was constructed using all individual standard materials and the slope of the curve was in good agreement with calculated absorption coefficients at the effective energy of the μCT scanner.