The formation of trace moisture by exposure of dry heated surfaces of 316 L stainless-steel, Restek Silcosteel(R), and nickel 1/8 in. outer diameter line segments to purified Ar and H-2 was studied using atmospheric pressure ionization mass spectrometry at flow rates of 2 slpm. Prior to H-2 exposure, adsorbed moisture was removed by heating incrementally to 500degreesC in an argon matrix, where the Restek Silcosteel(R) material released a maximum of 50 ppb moisture at 300 degreesC and moisture spikes from the Ni and stainless-steel surfaces reached several 100 ppb. Upon exposure to H-2, persistent low ppb moisture emissions due to the reduction of surface oxide species were observed at temperatures as low as 100 degreesC. Spikes at 300-500 degreesC ranged from similar to100 ppb for the stainless-steel lines,to 400 ppb for the Restek Silcosteel material. The observed moisture emissions have to be considered as a potential contamination source for high-purity processes utilizing H-2 purge at elevated temperatures. (C) 2004 American Vacuum Society.