Calibration constant determination

A variation of the Shepard Cane incorporates both electrodes on a single rod. A circuit diagram of this type of instrument is shown in Fig. 10.51. The single rod has a calibration constant, determined by the area of the positive electrode. At balance the resistivity is given by the resistance multiplied by the rod constant. This instrument is portable and simple to operate, but it cannot be recommended when accurate results are required. 

Prepare the solutions and measure the pH at one temperature of the kinetic study. Of course, the pH meter and electrodes must be properly calibrated against standard buffers, all solutions being thermostated at the single temperature of measurement. Carry out the rate constant determinations at three or more tempertures do not measure the pH or change the solution composition at the additional temperatures. Determine from an Arrhenius plot of log against l/T. Then calculate Eqh using Eq. (6-37) or (6-39) and the appropriate values of AH and AH as discussed above. 

An added benefit of the direct SEC-[n] calibration approach is that a new independent way of determining K and a values, using only broad MW standards, has also resulted. As few as three standards (or four, if all are narrow MWD) are needed to obtain both MW and [x]] calibration curves for a particular polymer-solvent system by using the broad-standard, linear calibration approach. From the experimental calibration constants of the two calibration curves, one can calculate K and a directly as described later. 

The CO2 signal was calibrated by comparing against the well-known amount of CO2 formation produced during oxidation of a saturated CO adlayer ( CO stripping ) [Jusys et al., 2001], determining the calibration constant K between the two signals via the relation... 

We also indicated in Section 6.2 that the calibration of an instrument for quantitative analysis can utilize a single standard, resulting in a calibration constant, or a series of standards, resulting in a standard curve. If a single standard is used, the value of K is the calibration constant. It is found by determining the instrument response for a standard solution of the analyte and then calculating K ... 

In order to calculate the kinematic viscosity, the calibration constant for the viscometer in question must be known. This calibration constant is often determined by the vendor before it is shipped, but it is also often checked by the user. In the calibration procedure, a fluid of known viscosity is tested so that the calibration constant can then be calculated ... 

First, the calibration constant of the viscometer is determined from the calibration data ... 

The procedure may start with the reference experiment, which, in the case under analysis, involved a solution of ferrocene in cyclohexane (ferrocene is a nonphotoreactive substance that converts all the absorbed 366 nm radiation into heat). With the shutter closed, the calorimeter was calibrated using the Joule effect, as described in chapter 8, yielding the calibration constant s. The same solution was then irradiated for a given period of time t (typically, 2-3 min), by opening the shutter. The heat released during this period (g0, determined from the temperature against time plot and from the calibration constant (see chapter 8), leads to the radiant power (radiant energy per second) absorbed by the solution, P = /t. ... 

The calibration constant K strongly depends on the instrumental specifications, geometry of the calorimeter (Kd), and the solvent thermoelastic properties (x ) It can be determined through a comparative assay made under the same conditions as the main experiment but using a photoacoustic calibrant instead of the sample compound. The calibrants are substances that have known values of (pm from independent measurements, or more conveniently, substances that dissipate all of the absorbed energy as heat (e/>nr = 1), like ferrocene [286] or ort/w-hydroxybcnzophenone [287]. Note that the computation of K is not really needed, because a direct comparison of the signals obtained with sample and calibration compounds allows it to be eliminated from the calculations. 

Figure 12, in which the calibration constant, k, in mm./sec. channel, is shown as a function of the analyzer address. In this manner the linearity of the velocity scale can be readily determined over the range of Doppler velocities of interest in most iron and tin Mossbauer experiments.]... 

The layer thickness determines the relative intensity of the layer and substrate peaks. Provided again that the stracture is simple (later chapters deal with cases that are not), then the intensity of the layer peak increases monotonically with thickness. The values and the calibration constant will depend on the particular system being measured and can be determined either empirically or by computer calculation. An example is shown in Figure 3.8. 

The speed at which a sphere rolls down a cylindrical tube filled with a fluid or down an angled plate covered with a film of the fluid also gives a measure of viscosity. For the cylindrical tube geometry, equation 35, a generalized form of the Stokes equation is used for any given instrument, where v is the translational velocity of the rolling sphere and k is the instrument constant determined by calibration with standard fluids. 

Vapor Pressure Osmometry. VPO is a very practical method for determining Mn values in a wide range of solvents and temperatures. Recently, results obtained with classical pendant-drop instruments showed a significant dependence of the calibration constant upon the molecular weight of the standards (8,9). On the other hand, with an apparatus equipped with thermistors allowing the volume of the drops to be kept constant, this anomaly is not observed (10,11). 

Newtonian and non-Newtonian calibration fluids were used to determine the necessary calibration constants for the impeller method. It has been previously determined that the impeller method is only valid for a Reynolds number (Re) <10. Impeller rotational speed and torque data from Newtonian calibration fluids of known viscosity were employed to determine the Newtonian calibration constant, c. Cone-and plate-viscometer data from non-Newtonian calibration fluids were used to determine a viscosity vs shear rate relationship. Impeller rotational speed and torque data of the non-Newtonian calibration fluids combined with a determined viscosity vs shear rate correlation were utilized to calculate the shear rate constant, k. The impeller method calibration constants allow the calculation of viscosity, shear rate, and shear stress data of non-Newtonian suspensions. Metz et al. (2) have thoroughly discussed the equations utilized in the impeller method. 

For a given rotational speed, the measured torque combined with fluid viscosity and impeller diameter can be used to determine the Newtonian calibration constant, c. 

Viscosity, shear stress, and shear rate can be calculated for any non-Newtonian suspension using the impeller method calibration constants. Viscosity is determined using Eq. 4. The shear stress can be calculated for any impeller speed and measured torque ... 

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