Multi-point calibration

Fluorescence lifetime imaging Multi-point calibration, minimum resolvable differences, and artifact suppression. Cytometry 43, 248-60. 

According to the number of standards used, the calibration procedures can be subdivided into Single-point calibration Two-point calibration Multi-point calibration. 

Multi point calibration will be recommended if minimum uncertainty and maximum consistency are required over a wide range of pH(X) values [21, 22]. The calibration function of the electrode is then calculated by linear regression of the difference in cell voltage results from the standard pH values. This calibration procedure is also recommended for characterising the performance of electrode systems. 

There are various ways to derive a calibration curve. Multi-point calibration curves, for example, include a minimum of three different concentrations of the analyte. For semiquantitative assays, a single-point calibration is common. The single point is usually the threshold concentration used to determine whether a specimen is positive or negative for the analyte of interest. Depending on the validation process and performance characteristics of the assay, a single-point calibration curve may also be used in quantitative applications over a limited range of linearity. A historical (pre-established) multi-point calibration curve may also be used, but only if the stability of the analytical method over time has been well established (Goldberger et al., 1997). 

Multi-point calibration is carried out using up to five standard buffers. The use of more than five points yields no significant improvement in the statistical information obtainable. 

The transition used to calibrate the temperature scale of a thermobalance should have the following properties [1] (i) the width of the transition should be as narrow as possible and have a small energy of transformation (ii) the transition should be reversible so that the same reference sample can be used several times to check and optimize the calibration (iii) the temperature of the transition should be independent of the atmospheric composition and pressure, and unaffected by the presence of other standard materials so that a multi-point calibration can be achieved in a single run and (iv) the transition should be readily observable using standard reference materials in the milligram mass range. Transitions or decompositions which involve the loss of volatile products are usually irreversible and controlled by kinetic factors, and are unsuitable for temperature calibration. Dehydration reactions are also unsuitable because the transition width is strongly influenced by the atmospheric conditions. 

The system can then search for the required peaks, find their centroids and fit an appropriate function to the pairs of position/energy data. In most cases, the choice of appropriate function will be determined by the system itself. A hardwired analyser is unlikely to allow more than a two point calibration. Even in an MCA emulator system such as Maestro-II, users are limited to a two point linear calibration. Using the companion full spectrum analysis program, GammaVision, this initial calibration can be replaced by a multi-point calibration fitted to a quadratic equation ... 

Transfer 0.2 mL blank serum/plasma, blood and/or urine, standards, controls, and patient specimens to appropriately labeled 12 x 75 mm tubes (see Note 5). Multi point calibrators are run in the beginning of an analytical run with controls interspersed throughout the run according to the QC standards established by a laboratory. The last sample of a run should be a low QC. 

Prepare the aforementioned standards and suitable dilutions for the calibration graphs to cover the three ranges. A computer included with the analyzer may be used, if an internal multi-point calibration curve is provided. 

The concentration of sulfur in the sample is read from the calibration curve using the averaged counts for each oil. Record the results to two decimal places. If the analyzer includes a computer and provides for automatic multi-point calibration, the concentration values so computed are to be recorded. 

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