for PS, except that the last holding time at 320 °C was lengthened by
20 min.
Quantification of POPswas performed by comparing the peak areas of
the IS (19-hydroxycholesterol) and their analog COPs,with calculation of
the Rf: 7β-hydroxycholesterol (Rf=1.14) for hydroxyphytosterols,
β-epoxycholesterol (Rf=0.72) for epoxyphytosterols, and 7-
ketocholesterol (Rf=1.15) for ketophytosterols. The Rf for 7-
ketostigmasterol (1.12) was calculated and compared with that
calculated for 7-ketocholesterol, to confirm the Rf values of the
COPs with respect to the POPs.