Performance of a corona ion source for measurement of sulfuric acid by chemical ionization mass spectrometry

The performance of an ion source based on corona discharge has been studied. This source is used for the detection of gaseous sulfuric acid by chemical ionization mass spectrometry (CIMS) through the reaction of NO(3)(-) ions with H(2)SO(4). The ion source is operated under atmospheric pressure and its design is similar to the one of a radioactive (americium-241) ion source which has been used previously. The results show that the detection limit for the corona ion source is sufficiently good for most applications. For an integration time of 1 min it is similar to 6 x 10(4) molecule cm(-3) of H(2)SO(4). In addition, only a small cross-sensitivity to SO(2) has been observed for concentrations as high as 1 ppmv in the sample gas. This low sensitivity to SO(2) is achieved even without the addition of an OH scavenger. When comparing the new corona ion source with the americium ion source for the same provided H(2)SO(4) concentration, both ion sources yield almost identical values. These features make the corona ion source investigated here favorable over the more commonly used radioactive ion sources for most applications where H(2)SO(4) is measured by CIMS.