The VG-5400 is a dedicated mass spectrometer for noble gas isotopes. It is a double focusing instrument with extended geometry.

It has a Nier-type ion source, an electromagnetic analyser, a Faraday collector with a 100 GOhm resistor, and an ion counter (SEM: secondary electron multiplier). The sample is admitted the mass spectrometer through a cryogenic preparation and purification line. The sensitivity of the mass spectrometer is 1×10^-3 A/Torr and 2×10^-4 A/ Torr for argon and helium, respectively. It enables us to detect even 5000 ³He atoms. The resolution of more than 600 at 3 amu allows us to resolve a ³He⁺ peak and H₃⁺/HD⁺ double peak. The tritium concentration of environmental water samples are determined via the mass spectrometric analysis of its daughter, ³He. The pressure sensitivity and hence the systematic error of the measurement of low level helium abundances are eliminated by adding an ultrapure 4He spike to each tritiogenic ³He samples. The 10-20 % of systematic error could be reduced below 2 permil. Besides tritium analyses, noble gases dissolved in groundwater are determined by the mass spectrometer. ³H/³He apparent ages and recharge temperatures can be calculated from the noble gas concentrations and helium isotope ratios. All these values are applied in the research of recharge areas and palaeoclimate.