"The U.S. Bureau of Mines has developed a mass spectrometer method for determining helium in the parts-per-million to 10-pct range to an accuracy of +/-1 pct. The method employs a mass spectrometer, an inlet system utilizing a chromatographic gas-sampling valve, and an activated coconut charcoal trap cooled with liquid nitrogen. Gravimetrically prepared standards of helium in nitrogen were used to demonstrate the linearity of the method over the concentration range of 10 ppm to 10.66 pct helium." - NIOSHTIC-2 NIOSHTIC no. 10009096

National Institute for Occupational Safety and Health