Characterization of a hydrogen flame as an ion source form mass spectrometry

A commercial inductively coupled plasma (ICP) mass spectrometer was modifie d to employ an air-hydrogen flame in place of the ICP as an ion source. A l iquid nitrogen trap was placed in the vacuum line to remove water. A very s imple intrinsic mass spectral background was obtained with the hydrogen fla me ionization mass spectrometry (FIMS). Molecular ions such as K(H2O)(+), N a(H2O)( +), Ca(H2O)(+) and CaOH(H2O)(x)(+) (x = 0-2) were observed when sol utions containing Na, K or Ca were aspirated, Although the presence of the molecular ions complicated the mass spectra, it also provided a wider choic e of analytical masses for an analyte. Isotope ratio measurements of Ca wer e made with both Ca+ and CaOH+ species at masses 40, 44, 57 and 61. Better isotope ratio precision was obtained at CaOH+ masses relative to there for Ca+ because the sensitivity was about 10 times higher. Isotope ratio measur ement of K wats made at masses 39 and 41. A ratio precision of about 0.2 an d 0.5% was obtained for K and Ca, respectively. The results suggest that th e FIMS is suitable for the isotope ratio measurement of K and Ca in simple matrices, and that the air-hydrogen flame is a more desirable ion source th an an air-acetylene flame for FIMS.