Calibrated reference

Calibration refers to characterizing the residence time in the GPC as a function of molecular weight. Axial dispersion refers to the chromatogram being a spread curve even for a monodisperse sample. A polydisperse sample then is the result of a series of overlapping, unseen, spread curves. 

Another aspect of traceability of the results is the linkage of data from the homogeneity study, the stability study, and the characterization study of the reference material. In order to establish this link, the coordinator must be in the position to demonstrate that the results of these three studies have a common reference. Such a reference can be a calibrant, reference material, or possibly some realization by means of a suitable method. If such a common reference is not available, it is impossible to link the data sets, and therefore it is impossible to translate the results from the homogeneity and stability studies to the characterization of the material. 

Molecular rotors with a dual emission band, such as DMABN or A/,A/-dimethyl-[4-(2-pyrimidin-4-yl-vinyl)-phenyl]-amine (DMA-2,4 38, Fig. 13) [64], allow to use the ratio between LE and TICT emission to eliminate instrument- and experiment-dependent factors analogous to (10). One example is the measurement of pH with the TICT probe p-A,A-dimethylaminobenzoic acid 39 [69]. The use of such an intensity ratio requires calibration with solvent gradients, and influences of solvent polarity may cause solvatochromic shifts and adversely influence the calibration. Probes with dual emission bands often have points in their emission spectra that are independent from the solvent properties, analogous to isosbestic points in absorption spectra. Emission at these wavelengths can be used as an internal calibration reference. 

In order to measure the exact amount of a specific protein (analyte) by IHC signal intensity, a critical requirement is the availability of a standard reference material (present in a known amount by weight) that can be used to calibrate the assay (IHC stain). It is then possible to determine the amount of test analyte (protein) by a translation process from the intensity of IHC signals. In this respect it is helpful to consider the IHC stain as a tissue based ELISA assay (Enzyme Linked ImmunoSorbent Assay), noting that ELISA is used in the clinical laboratory as a standard quantitative method for measuring protein by weight in fluids, by reference to a calibrating reference standard. 

The gas pycnometer is based on the ideal gas law. A known quantity of gas (characterized by a determined temperature and pressure) is allowed to flow from a calibrated reference volume into a calibrated sample cell containing the solid. A second pressure reading is obtained, and the sample volume is calculated. 

Plotting Calibration (Reference) Graphs Using the Least Squares Regression Method... 

A calibration (reference) standard shall be prepared from a representative sample. Longitudinal (axial) reference notches shall be introduced on the outer and inner surfaces of the standard in accordance with Fig. 2(c) of ASTM E 213 to a depth not greater than the larger of 0.1 mm (0.004 in.) or 4% of specimen thickness and a length not more than 10 times the notch depth. 

If it is established that a measuring device provides a value for a known sample that is in agreement with the known value to within established limits of precision, that device is said to be calibrated. Thus, calibration refers to a procedure that checks the device to confirm that it provides the known value. An example is an analytical balance, as discussed above. Sometimes the device can be electronically adjusted to give the known value, such as in the case of a pH meter that is calibrated with solutions of known pH. However, calibration can also refer to the procedure by which the measurement value obtained on a device for a known sample becomes known. An example of this is a spectrophotometer, in which the absorbance values for known concentrations of solutions become known. We will encounter all of these calibration types in our studies. 

Figure 2 serves to illustrate the remarkable reproducibility and precision of the spectra that are obtained. The upper trace shows the 950-1150 cm-1 region of the absorbance spectrum of 35 x 10 3 Torr (buffered to 700 Torr total pressure with ultra pure air and run at forty meters path length) of supposedly 90% pure methanol, as received from a supplier. The middle trace represents 12 x 10 3 Torr of methanol, as determined more than a year previously in the short auxiliary cell. The lower trace shows the difference. Note that the and ISq spectra are completely distinctive, that the 1 0 enrichment is in fact only 65%, and that in the region of spectral overlap perfect separation of the two spectra can be achieved in spite of their great complexity. Further, the lower trace, obtained using archival reference data, represents a calibrated reference spectrum for methanol, even though no purified sample has ever existed. 

Calibration refers to comparison with a standard in accordance with certain statutory regulations by specially authorized personnel (calibration facility). The result of this procedure is a calibration certificate which contains the deviations of the readings of the instrument being calibrated from the standard. 

Unless technically impossible, the accuracy and linearity of each measurement chain shall be checked at least at two different points of the measurement range. Visualization of values transmitted from the sensors to the system controller is made most often directly on the controller itself (screen or printer), using an appropriate submenu of the controller. The accuracy of the values read on the equipment or utilities instmmentation is checked by means of appropriate calibrated reference instmmentation traceable to national official standards. 

Unless technically impossible, accuracy and linearity of each output chain are checked. Visualization of values sent to the equipment is made either directly on the checked peripheral system or using appropriate equipment. Accuracy of values transmitted from the analog outputs is checked by using an appropriate calibrated reference instrumentation traceable to national official standards. 

Fig. 9.2. Constant-volume tensimeter. The sample tube (enlarged view, upper left) is loaded with solid in a dry box or by sublimation from the vacuum line. The lube is evacuated, sealed, weighed, then glassblown to the tensimeter. After evacuating and flame-drying the tensimeter, the mercury level is raised and the break-seal cracked. Since the mercury serves as the cutoff to the vacuum manifold, the sample is not exposed to grease, stopcocks, or joints. This design is desirable when very long equilibration times are necessary. The mercury level is adjusted at the volume-calibrated reference point, such as A on (he diagram, if it is important to know the gas volume in the apparatus.

The use of more calibration data can result in improved model performance, especially if the additional calibration data result in an improved representation of the sample states that need to be covered for calibration. Referring to the earlier plot of interference error and estimation error versus model complexity (Figure 8.18), an improved representation of the calibration space corresponds to a general drop in the level of the estimation error curve. This results in lower overall prediction error. 

After first employing MAP techniques for its own calibrations, NBS launched efforts to teach the concept to others. Detailed descriptions of how to implement the MAP concept for particular kinds of calibrations were published during the late 1970s and the 1980s by Croarkin, Varner, and others. References [8] and [9] provide two examples of MAP techniques for dimensional calibrations. References [10] and [11] (taken together) describe MAP techniques for maintaining dc voltage. 

Calibration Samples. Monodisperse polystyrene latices are available with known, narrow particle size distributions. Coefficients of variance about the mean diameter are typically less than 6% of diameter measured using electron microscopy (25). HDC typically cannot resolve differences in diameter of only 6%. Therefore, these polystyrenes are sufficiently narrow to be used as HDC calibration reference samples. However, doing so may result in incorporation of a systematic error in the particle size versus elution volume calibration, arising from known electron microscopy errors of as much as 5% for particles below 1 um (26). Therefore, accuracy can only be stated as relative to electron microscopy results for the calibration samples. FlowSizer performance specifications have been reported elsewhere (27) with diameter and mass percent results within 5% of those determined by electron microscopy for a series of these monodisperse polystyrene latices. 

However, for relatively new types of solar cells such as the polymer-based solar cells described here, suitable stable reference cells cannot yet be fabricated. This implies that, for measurements concerning these cells, calibrated reference cells are used (Si, GaAs) with a different spectral response to the device under test, resulting in mismatch factors that deviate significantly from 1. It is therefore of the utmost importance to carry out the procedure as precisely as possible in order to minimise measurement errors. 

To minimize line artifacts and establish a common time reference, (42) is usually rewritten in differential form, to compare reflected signals from the sample and a calibrated reference standard and thus eliminate Vo(f) [79-86]. 

Calibration and standardization are often confused and used interchangeably. Calibration refers to the process of adjusting an instrument or instrument s scale to a known physical standard [22], Wavelength scales are calibrated by comparing the instrument s wavelength scale to a spectral line whose value is known from first... 

Now, with the advent of reference materials, the term standard is too general to be used alone and it is, therefore, normal to specify the type of standard, e.g. analytical, calibration, reference material, etc. Use of the term standard(s) is, therefore, only appropriate in the most general of contexts. 

Sample Binding Energy of V2p3/2 and Ols/eV (FWHM) Eb Calibration Reference... 

Sample Binding energy of V2psp and Ols (eV) (FWHM) b Calibration Reference... 

Each calibrated reference source is supplied with a calibration certificate listing ... 

M. Moini, Ultramark 1621 as a calibrant/reference compound for MS. II. Positive- and negative-ion ESI, Rapid Commun. Mass Spectrom., 8 (1994) 711. 

Several uptake kits are commercially available, Tg uptake values for individual subjects depend on specific assay conditions such as incubation time and temperature, quantity and avidity of the binding material, and specific activity and choice of the label. To compensate for variations in uptake values, the percent uptake for each unknown should be determined by comparison with a calibrator, reference material, or euthyroid reference serum of Imown percent uptake. Almost aU commercial assays determine the percent uptake... 

Complex environmental monitoring measurements are generally based on successive analytical steps, such as extraction, derivatization, separation and detection. This succession multiplies the risk that the traceability chain is broken because of a lack of appropriate references (e.g. pure calibrants, reference materials). Reference methods usually refer to methods with high metrological qualities (they may actually be standardized methods), and examples are provided by primary methods that are directly traceable to SI units without the need to use an external calibration. 

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