ESI was conducted
using a capillary voltage of 3 kV. Nitrogen was used as the sheath
and auxiliary gas with the heated capillary set at 275 ◦C. MS–MS
spectra were obtained by collision induced dissociation (CID) of
the parent m/z, with the relative collision energy set at 35%. Identification
was based on the m/z values and fragmentation ions,
while quantification was performed using a laboratory reference
material (“A. Vogel Spilanthes”, Biohorma, Lummen, Belgium) with
spilanthol (0.11%, w/w) as the reference biomarker.