The MAT-253 Ultra—a novel high-resolution, multi-collector gas source mass spectrometer

We present the design, performance and representative applications of the MAT 253 Ultra – the first prototype of a new class of high-resolution gas source isotope ratio mass spectrometers. The MAT-253 Ultra is a forward geometry double focusing sector mass spectrometer with a Nier-type gas source. Samples are introduced through capilary bleeds from any of 4 automated flexible bellows and/or a carrier-gas port. Ions enter the analyzer through an adjustable entrance slit (5 to 250 m). The analyzer has a 23 cm radius magnet and is similar in scale and design to the Neptune Plus MC-ICPMS. The detector array consists of 1 fixed position and 7 moveable positions on 6 trolleys. An RPQ lens is positioned before the central detector position. Each detector position contains both an SEM and faraday cup detector; each faraday can be registered through any of 10 amplifiers varying in gain from 107 to 1012. Ion beams from m/z 1 to ~300 can be collected, with a ~15 % mass range for simultaneous collection. Useful ion yield is ~1 ion per 1200 molecules for CO2 under standard analytical conditions and using a 250 m entrance slit. The dynamic range in simultaneously measurable ion currents is ~1014. Backgrounds are negligible in the central detector position when the RPQ is in use, permiting quantitative analysis of low intensity ion beams even with high source pressures. Mass resolving power (M/¨M, 5%/95% definition) has been measured up to 26,000 and is routinely as good as ~22-24,000 — sufficient to separate most isobaric interferences among isotopologues of H-C-N-O-S molecular species; in particular, it permits separation of 13C from D isotopologues and both from H adducts in alkanes and related organics. Analyzer system stability is routinely < 2ppm/hour, permitting precise analysis of small features on complex peaks. External precision for isotope ratio measurements of relatively intense ion beams are routinely 10’s of ppm, relative; measurements of weaker ion beam using SEM detectors reach counting statistics limits down to external precisions of ~0.1 ‰. The MAT 253 Ultra enables many previously impossible isotopic analyses of gases and volatile organics and their fragment and adduct ions. Demonstrated examples include: G13C, GD and 13CH3D of methane; G13C of propane and many of its fragments (enabling position-specific 13C determination); direct analysis of G17O G18O, G15N and 15N-18O ‘clumping’ in N2O and its NO fragment; 18O17O and 18O2 in O2; and clumped isotope analysis of CO2 free of contaminant isobaric interferences