Mass Spectrometer

Abstract

An isotope ratio mass spectrometer has an ion source, a static field mass filter, a reaction cell to induce a mass shift reaction, and a sector field mass analyser for spatially separating ions from the reaction cell according to their m / z. A detector platform detects a plurality of different ion species separated by the sector field mass analyser. The static field mass filter has a first Wien filter that deflects ions away from a longitudinal symmetry axis of the spectrometer in accordance with the ions' m / z, and a second Wien filter that deflects ions back towards the longitudinal symmetry axis in accordance with the ions' m / z. An inverting lens is positioned along the longitudinal axis between the Wien filters to invert the direction of deflection of the ions from the first Wien filter. The static field mass filter provides high transmission and improved spectrometer sensitivity. The first and second Wien filters permit simple tuning.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a National Stage application filed under 35 USC § 371 of International Patent Application No. PCT / EP2019 / 056884, filed on Mar. 19, 2019. PCT Application No, PCT / EP2019 / 056884, claims priority to GB 1804386.9, filed Mar. 19, 2018, both of which are incorporated by reference herein in their entirety.FIELD OF THE INVENTION[0002]This invention relates to a static field mass filter for a mass spectrometer and a mass spectrometer, in particular, but not exclusively, for isotope ratio mass spectrometry (IRMS).BACKGROUND OF THE INVENTION[0003]Mass spectrometers are used to analyse the m / z ratios of ions which have been generated by an ion source from a sample. Before analysis, the ions might be further exposed to other processes in one or more reaction cells. Further mass filters may be used to reduce the amount of analysed ions by selecting only ions in a specific m / z range of a m / z window. Such a mass filter is arranged betw...

AI Technical Summary

Benefits of technology

[0036]In contrast to RF based mass filter technology, the static field mass filter works perfectly well with wide aperture high ion beam energy (typically KeV range) ion optics which ensures high transmission and thus high sensitivity of the complete mass spectrometer.

[0039]The resulting instrument may easily be tuned along the path of the ions, because there is a simple relationship between the electric and magnetic fields, and the mass to charge ratio of the ions. Internal normalisation algorithms for mass fractionation correction can thus be applied to achieve accurate results.

[0042]The high stability static ion optics permits high precision, high accuracy isotope ratio measurements. There is an inherent robustness against small drifts of instrument parameters with the symmetrical double Wien filter arrangement, because the same controller can be employed for both the magnetic and the electric fields. This means that any instability arising in a first of the Wien filters occurs equally in the second of the Wien filters, and the arrangement of the static field mass filter with first and second Wien filters separated by an inverting lens thus allows the instabilities in the Wien filters to cancel each other out.

[0043]Another advantage of the static field mass filter of the present invention is that it employs high ion energy ion optics (of the order KeV). This contrasts with RF mass filters that employ low energy ion optics. High energy ion optics provides for improved focusing conditions, leading to higher ion transmission. There is higher robustness against space charge—in ICP-MS, for example, there is an intense argon ion beam at the entrance to the pre-filter. Where the pre-filter is—in accordance with this invention—a static field mass filter, the resulting ability to employ higher ion beam energies reduces the effect of space charge which in turn reduces the degree of mass discrimination.

[0044]Higher ion energies also provide higher matrix robustness, particularly in the case of laser ablation, again as a result of reduced space charge effects.

[0045]In the static field mass filter of embodiments of the present invention, the ions are spread over their mass-to-charge ratio in the direction transverse to the flight direction (z-direction) of the ions. This avoids the mixing the of flight paths of ions in the direction transverse to the flight direction, which is a consequence of the use of quadrupole mass filters.

Problems solved by technology

This leads to a flat transmission of ions across a selected mass-to-charge ratio range and small deviations in system tuning do not change the measured isotope ratio in an unpredictable way.

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