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General detector parameters
In the chromatographic system, the detector has the task of converting a physically measurable property of the eluate from the column into an electrical signal. This signal is amplified and a chromatogram is created through visualization.
Linearity and dynamic range
In order to be able to detect samples over a wide concentration range without an additional calibration curve, the signal of the detector must depend proportionally in the linear range on the analyte concentration / mass. If the dependency changes outside the linear range, another calibration curve must be recorded in order to obtain meaningful data with the detector.
Sensitivity and Limit of Detection
In the linear range of the detector, the sensitivity is constant, since it describes the ratio of the detector signal to the concentration or mass of the analyte. The smallest amount of substance that can still be determined (in the carrier gas or eluent) limits the linear range downwards. It is assumed that a peak with twice the signal height is not drowned in the background noise.
Discontinuity, noise, drift
The cause of the background noise is the electronic signal processing. Control processes (e.g. temperature, pump system) are often the cause of periodic changes. In addition, sample residue that has gradually accumulated can degrade and affect detector behavior.
The general signal behavior of detectors can be divided as follows:
- the response sensitivity is the same or similar for many substances: universal detectors (examples: thermal conductivity detector, mass spectrometer)
- the response sensitivity is structure- or element-selective for individual components: selective detectors (examples: electron capture detector, nitrogen-phosphorus detector)