Impurity measurement in specialty gases using an atmospheric pressure ionization mass spectrometer with a two-compartment ion source

Using an atmospheric pressure ionization mass spectrometer (APIMS) with a two-compartment ion source, impurity in specialty gases (CH₄, SiH₄, GeH₄) is measured due to a stable ionization reaction with a detection limit of approximately 0.1 to 1 parts per billion (ppb). The form in which the impurity exists in these gases has been clarified. In the case of SiH₄, the main impurity is disiloxane (SiH₃-O-SiH₃). We have also established a method for obtaining the SiH₃-O-SiH₃ calibration curve standardized for a known concentration of SiH₃-O-SiH₃ generated from the reaction of SiH₄ with H₂O. In the case of CH₄ and GeH₄, the main impurity is moisture (H₂O) and it is quantified from the plotted H₂O calibration curve.