Retarding potential quadrupole filters

Highest isotope abundance sensitivity is needed to measure well very minor isotopes, e.g., to determine the age of a uranium sample (Wallenius et al. 2001). Use of tandem magnetic sectors or addition of an energy filter (Thermo Fisher Scientific, Patent 1993) like a retarding potential quadrupole lens (RPQ) (O Fig. 63.19) would do the job. 

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