Reference calibration

In the simplest case, experimental calibration can be carried out by direct reference measurements where the sensitivity factor b is given by the relation of measured value to concentration of a reference material (RM), b = yRvi/xRv,. Direct reference calibration is frequently used in NAA and X-ray analytical techniques (XRF, EPMA, TXRF). 

Measurements in living things, e.g. patients, is occasionally done by sampling in a non-invasive way. Because no standard patients are available which can be selected for calibration, another principle of calibration must be applied, e.g., by a reference method that measures parallel to the actual measuring method. So, the calibration consists in a comparison of the measured results with that of the reference method which are considered to be true (that have been validated beforehand). An example of a reference calibration is represented by non-invasive blood glucose determination by means of NIR spectroscopy (Muller et al. [1997] Fischbacher et al. [1997] Danzer et al. [1998], see Sect. 6.2.6). 

In contrast to the common calibration procedure measuring y — f xstandard) as shown in the front plane of Fig. (6.3a,b), the glucose reference calibration takes place in the base area of the three-dimensional model, xsampie = f ixstandard)> see Sect. 6.1.2. 

TABLE 5. Peak potentials Ep for oxidation of tetramethyllead and tetraethyllead on three different electrodes in AN 0.1 M EtaNCKV at 20°C, Ag AgCl reference, calibrated at +0.38 V vs 10 3 ferrocene116... 

Alanine dosimeters are based on the ability of 1-a alanine (a crystalline amino acid) to form a very stable free radical when subjected to ionizing radiation. The alanine free radical yields an electron paramagnetic resonance (EPR) signal that is dose dependent, yet independent of the dose rate, energy type, and relatively insensitive to temperature and humidity. Alanine dosimeters are available in the form of pellets or films and can be used for doses ranging from 10 Gy to 200 kGy. A reference calibration service using the alanine EPR system was developed and the scans were sent to the service center by mail. Currently the available system allows transferring the EPR scan to a NIST server for a calibration certificate. This way the procedure has been shortened from days to hours. ... 

Information concerning reference/calibration standard compound, potency, and reference for documentation of standard preparation. 

The value of e (under the conditions specified in Procedure) is 5.2 10" (a=1.9) at 545 nm. In the absence of acetate buffer, e values can be higher [16,17]. Hexamine buffer is recommended. The absorbance of the free reagent is insignificant at 545 nm. Solutions of the CAS-Al complex do not obey Beer s law. The intensity of the colour of the complex depends on the concentration of CAS. The colour weakens with increasing concentration of acetate. Alkali-metal salts affect the colour and its stability. To compensate for this salt effect, corresponding amounts of the salts should be added to the reference calibration solutions [19]. 

Between acquisitions there must be a delay sufficient for complete relaxation of the spins, and if signal averaging is used for each experiment, this must also be applied between each scan to obtain reliable calibrations. In proton spectroscopy, such delays are unlikely to be too much of a burden, but can be tediously long for slower-relaxing spins. If you have some feel for what the pulse width is likely to be, perhaps from similar samples or a reference calibration, then a better approach in this case is to search for the 360° null. Since magnetisation remains close to the - -z axis, its recovery demands less time and the whole process can be performed more quickly. The process can... 

The calcium and sodium activity coefficients were determined at 25.0 - 0.1 C with an Orion electrode (model 92-32) and a Radiometer electrode (model G502 Na), respectively. A saturated calomel electrode was used as the reference. Calibration curves were obtained using CaCl or NaCl solutions before and after each measurement. The CaCl2 and NaCl concentrations were measured by potentiometric determinations of the chlorides with silver nitrate and with a silver electrode. 

Two types of systems are commonly used power compensation and heat flux DSCs. In the power compensation apparatus temperatures of the sample and the reference are controlled independently by using separate but identical furnaces. The power input to the two furnaces is adjusted to equalize the temperatures. The energy required for the temperature equalization is a measure of the enthalpy or heat capacity in the sample relative to the reference. In heat flux DSC, the sample and the reference are interconnected by a metal disk that acts as a low-resistance heat-flow path. The entire assembly is placed inside a furnace. The changes in the enthalpy or heat capacity of the sample cause a difference in its temperature compared to the reference. The resulting heat flow is small because of the thermal contact between the sample and the reference. Calibration experiments are conducted to correlate enthalpy changes with the temperature differences. In both cases, the enthalpy changes are expressed in the units of energy per unit mass. 

Even Auger spectroscopy 26, 27), which is a powerful way of detecting the presence of various elements in the surface, is not foolproof regarding the absence of other elements. Sensitivities and calibrations for a given element seem to vary from one surface to another, and unless there is a reference calibration, absolute coverage determination is not possible, even by Auger spectroscopy. 

Aerial measuremait of surface activity on the ground Gamma spectrometCT system with NaI(Tl) detector and GPS Detailed information on spatial inhomogeneities in d osition R id Radionuclide-specific Costly Limited radionuclide id tifi-cation Ground reference calibration needed Limited to gamma emitting radionuclides Experienced staff needed... 

Gamma spectrometer with HPGe detector and GPS Costly Ground reference calibration needed Limited to gamma emitting radionuclides Normally liquid required ... 

Four grades are provided for in BS 5317 Reference, Calibration, grade 1 and grade 2. Reference grade bars are intended for use as reference standards and are of the highest accuracy. 

Once the reactive gas saturates the sample, the peaks areas acquired by the TCD (b, Figure 7) are equal to the reference calibration peak (a, Figure 7) and the analysis is over. In general, as for static adsorption analyses, the dynamic chemisorption is performed at constant temperature conditions (isotherms). The choice of the temperature depends on many factors such as type of sample and gas, type of information required, but it is very common to perform chemisorption at room temperature. Also the pre-treatments of the sample are effected in order to obtain a clean surface able to chemisorb the probe gas as described in 5.1. 

Only one inversion is now necesary. However, the drawback is that we need more references (calibration samples) than variables. Modern spectrometers supply hundreds of absorbances without any difficulty, but preparing so many samples is simply not viable. 

PIDs and FIDs have similar detection capability for VOCs in that the ionization process and signal collection of both are nonselective. Although very useful as VOC detectors, they are quite limited when nsed as field detectors for CWAs. Detection of CWAs can occnr only throngh the nse of response factors equivalent to respective calibration gas. Methane gas and isobntylene are nsed by FID and PID, respectively, as the reference calibration gas. Response factors correlate detector responses calibrated against the reference gases to a known concentration of a given compound. The usefulness of response factors, nnfortunately, is valid only if the sample contained the targeted chemical withont any other infinences (i.e. in a known situation). They are not viable CWA or TIC detectors becanse they do not provide specific... 

Fifty pesticides were selected and their reference calibrants of garanteed grade or equivalent were obtained from Kanto Kagaku (Tokyo, Japan), Hayashi Pure Chemical (Osaka, Japan), and Wako Pure Chemical (Osaka, Japan). Each stock solution (500mg/L) of the individual pesticide was prepared in acetone. Portions of all the stock solutions were combined in a volumetric flask and made up with acetone to prepare a mixed standard solution. Pesticides concentrations of working solutions for LC/MS analysis were prepared between 0.02 and 1 mg/L using acetnitrile. 

The QCT Calibration Phantom is designed and constructed to be used as an accessory to a CT scanner, as a reference calibration standard for comparing CT numbers of unknown materials to a known material. The Phantom is made up of a plastic base material, polyethylene containing 5 cylindrical holes (190 0.5 mm diameter). Each cavity filled with the reference solutions. Four cavities are filled with different solution of K2 HPO4 in distilled water provide a calibration for calculating the bone mineral density. We used 0, 50, 100 and 200 mg/cc solution of K2HPQ4 in distilled water and the fifth is a fat equivalent reference sample that it is filled with 60% ethanol [2]. 

Hence, it is possible to construct a standard curve relating viscometric measurements to steady-state anisotropy measurements for a particular fluid and use the quantitative relationship to determine the viscosity of the fluid by fluorescence polarization [4,9-11]. A standard curve in a reference calibration oil such as white paraffin oil can be used to determine the viscosity of another fluid as long as the calibration fluid is similar in dielectric constant and viscosity to the fluid being analyzed. It is important to keep in mind that the same fluorescent probe may display different behavior even in different hydrocarbon calibration oils, hence one must exercise caution when determining absolute values for microvis-... 

Note 6—The target calibration values used in this section are specific to the automatic vapor pressure instrument evaluated in the 1988 interlaboratory cooperative program. These calibration values do not necessarily correspond to the total vapor pressures or the dry vapor pressures (Test Method D 49S3) reported for the reference calibration materials, but rather are values that the instrument manufacturer suggests using to produce a dry vapor pressure equivalent reading on the digital display. 

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