3P-09 PDF
Enhancement of ionization efficiency by DC corona discharges in direct analysis in real time-mass spectrometry (DART-MS)
DC corona discharges were coupled with conventional DART to enhance ionization efficiency of DART. The combination of positive and negative corona discharges with conventional DART resulted in the formation of plasma jet, consisting of purple glow due to a large number of excited helium with 19.8 eV, between the DART source exit and corona needle. Analytes were desorbed and ionized by insertion in the plasma jet. The absolute intensities of (de)protonated analytes [M±H]± and [M±H]± with oxygen attachment and hydrogen loss observed were significantly increased compared with those obtained under conventional DART. In contrast, the species and relative intensities of fragment ions with respect to [M±H]± were same as those observed when using conventional DART, indicating of no effect of excited helium in the plasma jet on fragmentation processes. The present study showed, therefore, that the plasma jet occurring by combining DC corona discharges with conventional DART can significantly improve DART ionization efficiency without unnecessary secondary reactions.