In order to optimize the mass spectrometric conditions, thestandard solutions of AD, PF and the IS were respectively infused into the mass spectrometer by a syringe pump. According to the Q1 full-scan mass spectra, the protonated molecule ion [M+H]+wasinvisible for AD and also in low abundance for PF under the positiveESI mode. Sodiated adduct ions [M+Na]+were the base peak (thehighest abundance) for both analytes, and hence selected as theprecursor ions initially. But as the collision energy increased, thesignal intensity of [M+Na]+decreased significantly and no prod-uct ions were observed, which meant that [M+Na]+ions could notbe used as the precursor ions for the MRM detection of AD andPF. Afterwards, we found that ammonium adduct ions [M+NH4]+of the analytes and IS also produced high abundance by addingammonium acetate into the infusion solution. Moreover, the pre-cursor [M+NH4]+ions were fragile so that they could be fragmentedto generate abundant product ions with high yield [18]. Therefore,the [M+NH4]+ions at m/z 475.2, 498.2 and 406.2 were selectedas the precursor ions for AD, PF and the IS, respectively. On thebasis of that, to generate a high yield of stable and dominatingproduct ion from [M+NH4]+, mild collision-induced dissociation(CID) conditions such as low collision energy (CE) and low CADwere applied. The final MRM transitions used for quantificationwere m/z 475.2 → 163.1 for AD, m/z 498.2 → 179.1 for PF and m/z406.2 → 227.1 for IS (see Fig. 1).