Formation of the [M−1]⁺ Ions of Methylindoles in APCI Mass Spectrometry

Figure 3

Relationship between the m/z 130 [M−1]⁺ ions and m/z 131 M^+• ions of 2-methylindole and 3-methylindole studied by collision induced dissociation. (a) Collision energy resolved production curves of m/z 130 during CID of m/z 131. I130 and I131 are the absolute intensity of m/z 130 and m/z 131 ions, respectively. (b) Collision energy resolved total intensity (sum) of the m/z 130 and m/z 131 ions of 2-methylindole and 3-methylindole. (c) and (d) CID spectra of the m/z 131 ions of 2-methylindole and 3-methylindole, respectively, at 35% normalized collision energy.

(a)

(b)

(c)

(d)