Calibration basic

The linearity of the detector can be obtained by diluting the analyte stock solution and measuring the associated responses, while the linearity of the analytical method can be determined by making a series of concentrations of the analyte from independent sample preparations (weighing and spiking) [15]. It is also essential that the basic calibration linear curve be obtained by using independent samples, and not by using samples that have been prepared by dilution and injected into HPLC/GC, or spotted on one TLC plate. 

In the bioanalytical studies, the basic calibration should be prepared in the same biological matrix as in the samples of the intended study, which can be achieved by spiking the matrix with known concentration of the analyte. In this case, a blank sample, a zero sample (blank and internal standard), six to eight nonzero samples covering the expected range (including the anticipated QL) should be evaluated as part of the linearity study [27]. 

From the basic calibration of our method we can derive some performance characteristics of the method. This is important for method validation (see chapter 11)... 

The basic calibration of a method only covers the final measurement step without any preceding sample preparation. Pure analytical standard solutions are used here. Of course this does not cover the whole analytical process. So method characteristics for the basic calibration are not transferable to the whole analytical process. During validation the influence of other matrix constituents has to be investigated. 

For the basic calibration we will use sufficiently pure material which is free from interfering compounds. We have to ensure the homogeneity of the samples and the representativeness regarding the characteristics described in the slide. Of course the samples have to be sufficiently stable for the time period within which they are intended to be used. If necessary, we have to preserve the samples. Storage of the samples has to be organised in such a way that the integrity of the sample is not influenced. 

Preparation of standard samples always should be as accurate as possible Therefore gravimetric procedures should be preferred compared to volumetric ones and several dilutions should be avoided since each dilution step adds to the uncertainty. For a basic calibration we need 6 to 10 standard samples. They should be distributed equidistant over the whole working range. Linear regression requires equidistant distribution. Otherwise... 

What we have seen up to here is the basic calibration that delivers method characteristics for the pure physical measurement in the validation and re-validation procedure. Many analytical methods however require a frequent, sometimes daily calibration. Of course there is no need to have a 10 point calibration for everyday calibration. 

The basic calibration as described up to here is part of the (re-)validation of an analytical method... 

Most experiments described in Section 3.2.1 (with the exception of adsorption gravimetry) rely on the use of a calibrated volume. The basic calibration can be carried out in two ways directly or indirectly. Direct calibration implies that this part of the equipment can be isolated, removed and weighed (either evacuated or filled with dry air), filled with an outgassed liquid of known density and then weighed again. 

Some care should be exercised when using coated thermocouples since the response of the probe strongly depends on the coating. Although a calorimeter is important for the basic calibration of transducers, the calorimeter itself of little interest for sonochemical studies, unless it is used as the reactor. 

The method which seems to be soundest and most free of empirical complications from the point of view of basic calibration is interferometry. The calibration is derived from fundamental optics. A technique for dealing with the effect of pressure on the refractive index of the fluid is available via the Lorenz equation. An implicit difficulty is the effect of temperature on the density of the fluid and thus on the evaluation of the Lorenz equation. The necessity of passing the light through a flat transparent plate to form the fringes imposes some limitations on the applicability of the method. 

Usually, the manufacturer provides a basic calibration for each sensor. In many cases it is linear. Careful calibration with high resolution may detect any small non-linearity in this basic calibrations (see Muller et al., 1995, for examples). However, it is recommended not to change the basic calibration coefficients, but rather add corrections to these. 

The basic laboratory calibration of a conductivity cell is obtained by immersing the cell with the CTD in tanks filled with seawater of different salinities. To avoid effects of thermal expansion of the cell on the calibration, all bath temperatures are kept the same to within 2 K. The basic calibration Cctd of the conductivity cell is referred to the conductivity of the baths and is valid for the overall bath temperature and at atmospheric pressure. 

Pressure, temperature and conductivity measurements are converted into physical units in their basic calibrations, Pctd, 7 ctd and Cctd- This includes all necessary special corrections needed for certain CTD types. Preliminary salinity 5ctd is calculated. 

A basic calibration procedure is required to adjust the spectrophotometer amplifiers to convert the two measured light intensities, I (sample) and /q (optical or electronic reference), into the correct solution of the term log foil), Le., the absorbance as defined by Beer-Lambert s law (see Section 10.2). Mechanical or electronic simulation of an intensity Z = 7o must result in a zero photometer output. The linearity of the absorbance output should be checked by measuring a standard dilution sequence (see Section 10.2.4). 

Calibration of an Analytical Method (Basic Calibration) 565 The residual standard deviation is then ... 

Basically, calibration gas mixtures are produced by combining defined quantities of different components. The preparation methods are characterized by special features ... 

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