A reference mass spectrum (Fig. 2a) was collected using GINDEESI-MS from a blank day cream sample. Fig. 2b exhibits the GIND-EESI-MS mass spectrum recorded for 1 min from a skin care product spiked by 10 ppb oxybenzone, showing the abundant peaks ascribed to the protonated molecules (m/z 229) and the sodiate molecule (m/z 251). In comparison with the reference spectrum (Fig. 2a), no signals were detected with significant abundances at
either m/z 229 or m/z 251 although other background peaks were
detected at relatively high signal levels (∼103, cps), indicating that
no oxybenzone was detected in the blank sample. The protonated molecules (m/z229) produced major fragments ofm/z211, 151 and 105 during CID, by the loss of water, benzene, and C7H8O2, respectively (inset of Fig. 2b). The abundant peak at m/z 151 showed that
the cleavage of benzene was highly favored in the CID process. In
the MS3 spectrum (inset of Fig. 2b), the major fragments of m/z
151 further fragmented into ionic species, such as ions of m/z 123 and 95 by the loss of CO and CO, successively. These characteristic
fragments matched those obtained using the authentic oxybenzone, confirming the detection of trace analytes in the viscous
sample.