The Nu Instruments Noblesse is a single focusing mass spectrometer based upon a 24 cm radius, 75 degree magnetic sector. The mass spectrometer volume is 1.89 L (measurement includes inlet hose & source getter volumes). The Noblesse's “bright” Nier ion source, quadrupole zoom lens optics, and detector filters acheive high sensitivity (typically 12.5 Amps/mol at 300 mA trap current and 6kV accelerating voltage) and finely focused ion beams. Collectively these attributes facilitate resolution of partially overlapping mass interferences on noble gas peaks. The microprocesser-controlled zoom optic system permits "in-run" change of mass dispersion and ion beam tuning that allows use of a fixed three collector array. The Stanford Noblesse instrument (NG 021) is fitted with a faraday detector (1011 Ohm) and three ion counting ETP multipliers. The faraday cup or ion counter are selected dynamically for measurement behind the high mass exit slit. The axial and low mass exit slits are fitted with ion counters with chicane electrostatic filters that block stray electrons or ions that can degrade peak shape. 40Ar/39Ar measurements involve a single peak hop (40Ar, 38Ar, 36Ar measured together followed by 39Ar, 37Ar). Multicollector measurements are standardized by analysis of a 40Ar-39Ar-38Ar-36Ar reference gas using the exact same measurement sequence used for unknowns. Long term reproducibility of multicollector measurement of 40Ar/39Ar is typically 0.1 per mil.