In the EDD, measurements are recorded on known matrix with negligible autofluorescence. Resolving SC fluorescence from that of co-deposited flavoring compounds presents the greatest challenge to detection. Direct spectral measurements were performed on filters removed after actuation of e-cigarettes containing a range of commercially available eliquid, as to assess the impact on SC emission. From Figure , of 13 exemplar e-liquids, the major emission band from flavoring compounds is localized in the spectral region ~400-450 nm, red-shifted from SC emission by ~50 nm. On comparing to spectra acquired for identical e-liquids containing 1.5 mg/mL MDMB-4en-PINACA, we see that SC emission is resolved from that of the flavoring compounds (Figure ). We note that in some instances, emission is convolved of SC and flavoring compounds, however, a spectral feature is still present at ~350 nm. Figure shows how indole-based SC fluorescence is also resolved in the presence of flavoring compounds, with spectra of corresponding unaltered e-liquids shown in Figure . We posit that the variation in magnitude of SC emission is due to differential quenching occurring in e-liquid variants with different chemical composition. Taken together, these data indicate that sensitive, on-filter detection of SCs in the heterogenous mixture of commercial e-liquid is possible with the EDD.