Sample extraction
For each of the whales, we processed ten replicates, approximately 0.4 g
of blubber each: five endogenous (un-spiked) and five spiked with 400 µL
of a calibrant mixture of the 11 target analytes (masses in
Supplementary Table 2). In addition to three blanks, we ran three
un-spiked replicates from a standard reference material (NIST SRM 1945),
taken from a pregnant female short-finned pilot whale. For
quantification, we diluted neat standards in methanol to create ten
calibration standards covering a physiologically relevant range of
concentrations (Supplementary Table 2). We created an IS mix with ten
isotopically labeled matched ISs (Supplementary Table 2), which we added
to all samples (blanks, SRMs, calibrants, and blubber) before
extraction. We prepared all stocks and samples gravimetrically and
extracted all samples, including blanks and calibrants, using a bead
homogenization and QuEChERS extraction protocol previously detailed (6).