Total ion chromatograms of BO samples maintained at a surface pressure of 0.5 mN/m for 0, 60, and 120 minutes are shown in
Figure 4 with the mass spectra corresponding to the peaks. Three major components were detected: (1) BO (mass 590.6 amu) had a retention time of 42.6 ± 0.4 minutes and was detected as (M + H)
+, (M + NH
4)
+, and (M + Na)
+ ions. Fragmentation around the ester moiety was observed in collision-induced dissociation (CID) (
Supplementary Fig. S2A), similar to that observed previously for WEs.
15 (2) A more polar component was observed as a double peak with retention times of 23.2 ± 0.2 minutes and 25.2 ± 0.2 minutes. This molecule was detected as (M + NH
4)
+, (M + Na)
+, (M + K)
+, and (M + 59)
+ ions and had a molecular mass of 638.5 amu. The identity of the 59-amu adduct is unknown, but it has been also previously detected in ESI-MS with methanol- and acetic acid–containing eluent.
16 The 48-amu increase in mass compared with BO indicated that this compound was an ozonide. In addition, CID showed characteristic fragmentation around the 1,2,4-trioxolane ring
17 (
Supplementary Fig. S2B), confirming the identity of this compound as a BO ozonide (BOoz). Same fragments were detected for both peaks, indicating that the ozonide is present as
cis- and
trans-isomers, as has been previously detected for secondary ozonides.
17 (3) An even more polar component was detected with a retention time of 5.3 ± 0.1 minutes and mass of 480.4 amu. Multiple adducts were detected, including (M + H)
+, (M + 15)
+, (M + NH
4)
+, (M + MeOH + Na)
+, and (M + MeOH + 59)
+. This mass corresponds to a typical ozonolysis product, behenyl 9-oxononanoate (Boxno). The (M + 15)
+ ion is possibly an oxocarbenium ion formed in a reaction with methanol in the ionization process as has been reported previously for aromatic aldehydes.
18 In CID, fragmentation around the ester moiety was observed, identical to BO (
Supplementary Fig. S2C). In addition to the three main peaks, several peaks with smaller retention times were observed (
Supplementary Fig. S3). However, these peaks were ignored, as they were also observed in a blank sample and were putatively identified as sodium acetate clusters, phthalates, and Irganox-antioxidants likely originating from the solvents and containers used for collecting and handling the samples.