Quadrupole ion trap analysers

The maximum resolution is given by expression 16.16 for an ion carrying a unit charge e, accelerated under a PD of volts at the entrance to a filter of length L and of radius by using a radiofrequency whose maximum voltage 

The functioning principles can be discussed as follows the compound is submitted to a very brief electron bombardment yielding ions which subsequently penetrate the central part of the filter. A radiolfequency voltage is then applied to the annular electrode that confines these ions to the central space, by forcing them to follow complex trajectories in the presence of a low pressure of helium, of about 0.01 Pa, introduced to the trap as a form of shock absorber. 

To analyse the ions present, the radio frequency amplitude is increased gradually to destabilize the ions. One by one, in the rising order of m/z ratio. 

These small volume and high sensitivity instruments have, however, the inconvenience of operating over a narrow dynamic range and with an average reproducibility of spectra from the same sample, which represents a serious disadvantage in quantitative analysis. 

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Figure 2.243 Linear mass calibration of the quadrupol ion trap analyser (voltage of ring electrode against m/z value).

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