Response Functions and Limits of Detection

The limit of detection of a method (or limit of quantification for a dosage method) is a very important parameter. To compare this parameter in quadmpole and ion trap operations, the acquisition mode of the mass spectrometer must be made precise. 

Response functions obtained in full scan mode with a quadrupole and an 

In terms of detection limits, the performances of the quadrupole and ion trap are inverted with more specific acquisition modes such as SIM and SIS. SIM in quadrupole supplied limits of detection (and quantification) inferior to those in SIS with an ion trap. The demonstration of performances in SIM is described in Chapter 5 dedicated to acquisition modes. SIS proved less efficient because the isolation of an ion is much less precise with an ion trap than with a quadrupole. Furthermore, the molecules eluted from the chromatograph when the ion trap is not in ionization phase (internal source) or filling mode (external source) are not ionized and therefore not detected. This is not the case with a quadrupole that continuously detects the ions of interest. 

In summary, ion traps supply limits of detection that are inferior to those obtained with quadrupoles in scanning mode. Quadrupoles and triple quadrupoles supply detection limits that are inferior in SIM and MRM, respectively. That is why ion traps are useful for identifying substances and quadrupoles are normally used for quantification. Ion traps can also quantify analytes quadrupoles and triple quadrupoles can characterize molecules at higher concentration levels. 

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