Facile Atmospheric Generation of Water Radical Cations via TiO 2 ‐Nanoneedle Arrays for Aromatic Hydrocarbon Detection Based on Corona Discharge

Water radical cations, (H 2 O) n +• , have attracted considerable attention owing to their potential practical applications in analytical chemistry, structural chemistry, radiotherapy, and radiochemistry. Recently, atmospheric pressure chemical ionization has emerged as a versatile method for direct mass spectrometric analysis. Usually, H 3 O + is the major proton donor during ionization and only the pseudo molecular ion peaks, instead of molecular ions are detected. In this work, (H 2 O) 2 +• ions with high oxidizability and reactivity were generated using hydrothermally grown TiO 2 nanoneedle arrays in combination with a linear ion trap mass spectrometer under low operating voltage and applied to the direct mass spectrometric analysis of a mixture of volatile aromatic hydrocarbons. (H 2 O) 2 +• ions were generated with a high absolute ion current of up to 1.07 × 10 5  counts/s at atmospheric pressure. Using the generated (H 2 O) 2 +• as the primary ion permitted the tandem mass spectrometric analysis of a mixed vapor sample of aromatic hydrocarbons.