1C-O2-1820 PDF
Instrumentation and Method Development of On-site Analysis of Helium Isotopes Using a Multi-turn Time-of-Flight Mass Spectrometer
Helium isotope determination may be useful in measuring volcanic activity and earlier warning of possible eruptions. A method is presented for measuring the 3He/4He ratio in a gas sample by the multi-turn time-of-flight mass spectrometer infiTOF-UHV (MSI-Tokyo Inc., Tokyo Japan) (infiTOF). In contrast to conventional waveform averaging, peaks are determined by ion pulse counts from each time-of-flight trigger. Samples were also measured by conventional magnetic-sector mass spectrometry, and results were used to designate a secondary standard for infiTOF measurement and provide a ratio for each sample for comparison to infiTOF results. Mass assignment error for 3He+ was 4.30 x 10-5 Da. Mass error for 4He2+ and 3He+ for sample cylinders was 3.00 x 10-8 Da and 2.25 x 10-4 Da. Ratios determined by infiTOF were found to be within 2% of the ratios determined by magnetic-sector mass spectrometry. Mass drift was found to be less than 50 x 10-6 Da over ten hours. Flow was not found to affect the results as long as the reference sample was analyzed under the same conditions. Results indicate that the infiTOF system may be a viable tool for measuring helium isotopes, which may eventually lead to earlier warnings of volcanic activity.