 Metals were a class of material that could not be previously ionized by thermal ionization (the method formerly used for ionizing solid sample).Spark ion sources were not commercially produced until after 1954 when Hannay demonstrated its capability for analysis of trace impurities (sub-part per million detection sensitivity) in semiconducting materials.The prototype spark source instrument was the MS7 mass spectrometer produced by Metropolitan-Vickers Electrical Company, Ltd. in 1959.