What types of calibration are there

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Quantitative analysis

Detector behavior - response

The detector signal of an analyzer is strongly dependent on the concentration or the mass of a compound. In order to be able to quantify analytes precisely, the detector must be calibrated with a known sample amount. The range that is calibrated should at least cover the expected concentration range of the analyte in the samples. In each quantitative evaluation, the signal size of the detector for an analyte is compared with that of a standard.

The detector sensitivity (also referred to as the response factor) is defined as the ratio of the signal size to the concentration or mass of the analyte for constant analysis conditions and analyte amount.

The display sensitivities of the detector for different analytes are substance-specific and depend on the measurement method, the detector behavior and the evaluation method. The response of a detector is used as a property to compare different detectors or to give other verbal, qualitative statements regarding response behavior. To determine the concentration, the response factor must be used in reciprocal form (called the calibration factor). However, this should be avoided and an up-to-date calibration using several standard solutions should be preferred. These take into account the current status of the measuring system and, depending on the method, also the steps of the sample treatment.

calibration

Calibration is the generation of a mathematical model that describes the signal size as a function of the concentration of an analyte. For this purpose, one or more standard solutions of different concentrations are always measured. Their signal quantities are then used for modeling. The resulting calibration function has a limited validity (time, device, measuring parameters, measuring range, etc.). In order to be able to determine the concentration of the analyte from signals from samples with this model, the analysis function must be formed from the calibration function.

Calibration function
Analysis function

There are several methods of using an analytical system for quantification. The following methods are described in this teaching material:

  • Calibration with standard solutions (calibration via external standard and calibration function)
  • Calibration with standard solutions that also contain an internal standard
  • Standard addition
  • uncalibrated calculation method (normalization method)

These measurement methods, which require the methods mentioned above, are so-called relative methods. In contrast to this, there are the absolute methods that do not require calibration against standard samples of known concentration. These methods are e.g. gravimetry and titrimetry. Such methods also require reproducible chemical conditions (e.g. stoichiometry, standard solutions) and "calibrated" measuring and laboratory devices (e.g. burettes, scales).