We first tried to figure out if methylene was eliminated as formaldehyde in the microdroplet-driven double C-N breakdown by using high-resolution mass spectrometry (HR-MS). Due to low ionization efficiency of formaldehyde in electrospray ionization, dansyl hydrazine was utilized as a high-efficiency derivatization agent. A formaldehyde standard and two crude collected solutions from the microdroplet and bulk reactions were offline reacted with dansyl hydrazine in 1% acetic acid acidic methanol prior to HR-MS detection. As shown in Figure a&b, the hydrazone product of formaldehyde with dansyl hydrazine was clearly detected as its protonated form at m/z 278.0953 (mass error 1.80 ppm), and the abundance ratio of hydrazone to dansyl hydrazine (m/z 266.1) from the collection solution by the microdroplet reaction was apparently higher than the formaldehyde standard. As a comparison, the hydrazone peak detected from the reaction mixture of bulk phase after 8 hours reaction was much lower than its microdroplet counterpart. In addition, two additional peaks at m/z 298.1 (corresponding to the protonated vicinal diamine product 2a) and 310.1 (corresponding to protonated imidazoline derivative 1a and rearranged benzofused N-heterocycle 3a)