A novel variable dispersion zoom optics for isotope ratio sector field mass spectrometer

Aperture of collectors in multiple Faraday Collector system is limited to typically 1 mm due to limited dispersion of ion beams of different masses and this in turn makes it difficult to achieve required peak flatness on all collectors. Further, for analysis of different elements, positions of collectors need to be mechanically adjusted from outside the vacuum system and this makes the collector system very unwieldy. To circumvent these problems, a new collector system based on variable dispersion zoom optics has been developed that facilitates fixed collector cups with wider apertures. The collector position adjustability is replaced by the variability of the dispersion using a DC quadrupole followed by deflection optics that provides matched peaks with increased peak flatness for different elements. Advantage of new optics has been demonstrated by 87Sr/86Sr isotopic ratio measurement whereby precision has been improved to 8 ppm compared to 23 ppm obtained with the conventional collector setup on the same instrument.

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► Development of variable dispersion zoom optics for thermal ionization mass spectrometer has been carried out.
► Aperture of collectors has been increased from 1 mm to 3 mm.
► Improvement in peak flatness and precision of isotopic ratio measurement is demonstrated.
► The system increases mass range for multi-collector isotopic ratio measurement.