Calibration substances

First, the zero line is recorded using two empty crucibles. Next, a calibrant substance (usually alumina, i.e., synthetic sapphire) is placed in the sample crucible and the temperature program is repeated. Finally, the calibrant is replaced by the sample under study (keeping the crucible) and the temperature program run a third time. Based on equations 12.20 and 12.21, it can be concluded that the ordinate difference between the traces of the calibrant curve and of the zero line obtained for a given time t leads to the corresponding value of fcp ... 

H. K. Cammenga, W. Eysel, E. Gmelin, W. Hemminger, G. W. H. Hohne, S. M. Sarge. The Temperature Calibration of Scanning Calorimeters. Part 2. Calibration Substances. Thermochim. Acta 1993, 219, 333-342. 

If a calibrating substance, e.g., a fatty acid, saturates Asp, the total number of adsorption sites is... 

As mentioned in Section 8.3.2, the instrument must be calibrated with a substance of known molecular weight. The experimental conditions, i.e., solvent and temperature, must be strictly identical with those used for lignin samples. The calibrating substances usually employed are benzil (M = 210.2 g mol ) and sucrose octaacetate (M = 678.6 gmol ) with concentrations, m, in the range between 10 2 and 10 molkg-1. 

In fact, theory can provide explicit functions for (a) and (b) but values for these constants are usually obtained from calibrating substances of known molecular weights and molecular radii. Furthermore, each photocell will not have precisely the same response to low levels of light intensity and consequently calibration procedures are also necessary to take their different responses into account to provide appropriate correction factors.. 

The Raman intensities of several rotational and rotovibrational lines of or N2 are accurately known, and it is straightforward to express CILS intensities relative to these known intensities. This can be done by either adding a small amount of the calibration substance (H2) to the gas under investigation ( internal standard ) or by using separate gas cells for the two ( external standard ). 

Calibration is effected by means of six calibrators contained in the kits. The relevant graph is stored in the apparatus and is re-plotted whenever the reagent batch is changed or if a technical change is made in the instrument. The sample rotor is filled with 2 vessels each per calibrator. The calibrators consist of a human serum base into which the appropriate calibrator substance has been weighed with the exception of free T4. 

In situ pressure measurements within the diamond anvil cell are performed by means of calibration substances that are embedded in the pressure chamber together with the sample and the transmitting medium. Frequently used... 

EXAMPLES OF RECOMMENDED CALIBRATION SUBSTANCES AND FORMS WITH PRECAUTIONS FOR USE AND STORAGE — ORGANIC SUBSTANCES BASED ON REF. [23)... 

All common gases exist in very pure forms and can serve as calibration substances in routine measurement. It is, together with metal analysis, the best provided field in terms of primary reference materials. One important producer is NMI, who has developed several procedures to produce gases traceable to the mole of substance. NIST has also a large offer in pure gases. All commercially important industrial gases are nowadays available. Toxic gaseous substances are not yet all available. 

In cases where methods are similar or show common steps, it is essential to examine if no systematic bias is affecting the results. In some few cases, BCR was confronted with situations where participants had to use a common calibration material (certification of dioxins and furans in a fly ash extract). Such a situation offers the possibility of introducing a systematic error into the study and consequently of a bias of the certified value. Situations where suppliers cannot propose reliable calibration substances may oblige the certification body to provide a common material. It should remain an exception and if unavoidable, the producer of the common calibrant should follow a strict preparation procedure similar to the one described above for the certification of calibrants. 

In recent years great advance has been made in instrumentation for ORD and, in particular, for CD measurements [see, for example, Refs. (32—39,17)]. The improvements in measurement of CD within an absorption band enabled progress in the determination of the optical activity of conjugated protein molecules, particularly for systems of relatively small activity. A frequently used calibration substance for CD instruments is (+)-camphor-10-sulfonic acid in aqueous solution. In order to achieve correct calibration, optical rotation values of the calibration substance should be transformed to CD values used for standardization (40, 41). 

As previously discussed in Chapter 5, the DTA or DSC curve consists of a series of peaks in an upward or downward direction on the AT or heat-flow axis. The positions (on the temperature or X axis), shape, and number of peaks are used for purposes of qualitative identification of a substance, while the areas of the peaks, since they are related to the enthalpy of the reaction, are used for quantitative estimation of the reactive substance present or for thermochemica determinations. Because of the various factors which aflect the DTA or DSC curve of a sample, the peak temperatures and the shape of the peak are rather empirical. Generally, however, the curves are reproducible for any given instrument, so that they can be useful in the laboratory. By use of various calibration substances, the areas enclosed by the curve peaks can be related to heats of reaction, transition, polymerization, fusion, and so on. Or, if the heat of the reaction is known, the amount of reacting substance can be determined. 

The standard DSC heat-flow calibration procedure with indium is not longer accurate enough, due to the change from a closed to an open cell system (the standard platinum cell lids are removed). Demineralised water is used, therefore, as calibration substance for the vaporisation experiments. The heat of vaporisation of demineralised water was measured six times which each of the sample cups. The average heat of vaporisation measured was compared with the known heat of vaporisation of water (43.9 kJ/mol., [20]) to calculate a correction factor for each sample cup ... 

In fact, theory can provide explicit functions for (a) and (b) but values for these constants are usually obtained from calibrating substances of... 

The correlation coefficient for 1 % weight loss is r = 0.986, for 5 % r = 0.994, and for weight losses exceeding 10 % the correlation coefficient increases to / > 0.997. The coefficients of equation 3-3 are different for each weight loss and decrease at increasing weight losses (Fig. 3-18 and 3-19). The ascertained functions are always of the same kind regardless to the type of thermobalance or the series of calibration substances, but the coefficients are, naturally, different. Nevertheless there is a linear relation between the data... 

Various instruments have been constructed for measurement of the capacity or capacity increase. In the early research, primarily instruments based on electrostatic methods were employed, e.g., those utilizing Coulomb s law [Fu 24] or static capacity measurement [Op 33]. Later, instruments based on alternating current capacity measurement gained preference. Among these can be listed the instruments based on the classical bridge method [Ad 64, Ga 50], the resonance methods [Im 65, So 64] and the heterodyne method [Ba 51, We 51]. All of these can be used only for relative measurements. The dielectric data sought are obtained by comparison with known calibration substances. Instruments based on the... 

Since the various calibration substances have different molecular weights, the reference substance for calibration should be specified when the content is given in mg/L... 

An advantageous and highly sensitive method of determining the bismuth content is to use ICP-AES (Chapters 2 and 3) on a separate concentration. The result may then be referred to nonionic surfactant, taking into account the calibration substance etc. 

Table 17.9 Melting points of calibration substances for the Kofler hotbench...

PEO 2000 for synthesis (Merck-Schuchardt) was chosen for osmotic vapour pressure measurements. Fructose p.a. (Fa. Merck) was used as calibrating substance. For the membrane osmosis PEO 35000 (Hoechst AG) was taken. This product was fractionated by slowly cooling a solution (10 wt.% PEO) of a mixture water/acetone (15/85 wt./wt.). This procedure was carried out to make sure, that the sample doesn t contain portions of low molecular polymers <20000 g/mol. The membranes (Sartorius, Gottingen, regenerated cellulose Cat.-Nr. 11539) have a lower limit for determination of molar masses of 20000 g/mol. 

In Figure 8 the spectrum of approximately 20 nanograms of isobutyl methacrylate (which seems to be the calibrating substance for determining sensitivity in GC/FT-IR) is shown The spectrum was obtained from a... 

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