SIRIX: A NEW STABLE ISOTOPE RATIO MULTI-COLLECTOR MASS SPECTROMETER FROM ISOTOPX

Stable isotope ratio mass spectrometry (SIRMS) allows highly precise and accurate isotope ratio measurements of H/D, ¹³C/¹²C, ¹⁵N/¹⁴N, ¹⁸O/¹⁶O, ³⁴S/³²S (from SO₂ and SF₆), ²⁸Si/²⁹Si as well as Ar, Kr and Xe isotopes. In recent years measurement of isotopologues or “clumped isotopes” have become more widespread. Much focus is on the analysis of CO₂ where isotopes of mass m/z 44, 45, 46, 47, 48 and 49 are of interest.

The new SIRIX mass spectrometer from Isotopx is the latest version of this type of mass spectrometer. It features advanced multi-collector technology in combination with a high sensitivity and high mass resolution spectrometer design. The objective is to provide a powerful, versatile, sensitive, stable isotope mass spectrometer that is intuitive to use, which can also be optimised for the most exacting applications.

Ultimate precision in stable isotope mass spectrometry requires detector and amplifier stability previously not achievable. Existing instrumentation requires the switching between sample and reference gas of the order of every 30s to continually “calibrate” the instrument. Each switch between sample and reference gas has a corresponding delay/settle period for the beam intensity to settle. As a result, the duty cycle of sample gas can be well below 50%.

With the development of the ATONA and new extended range ATONA, Isotopx has successfully managed to improve performance and stability of the amplifier system. The exceptionally quiet and stable amplifier allows for extended measurement times of sample gas; increasing duty-cycle.

This paper details the new mass spectrometer design and performance of the ATONA amplifier technology when used in stable isotope applications and beam currents. Comparisons with traditional technologies are made and advances in analytical techniques that are now possible are considered.

We highlight efforts to improve instrumentation by increasing measurable signal currents and reducing background interferences which are factors limiting analytical precision and analysis times.