2.2 Odorants preparation
This experiment used three odorants, namely tetrahydrothiophene,
2-methylpyrazine, and trimethylindole, purchased from Aladdin Company
(Shanghai, China). Appropriate amounts of the above three odorants were
added to a felt-tip pen (Burgart Messtechnik, Wedel, Germany). Regarding
the safety of the odorants: first, after adding an appropriate amount of
the three odorants, the pen can be used for 6 months without adding
odorants again during the period. Also, the amounts of
tetrahydrothiophene, trimethylindole, and 2-methylpyrazine used in this
experiment were 1 mg, 2 mg, and 300 mg, respectively. A-fter animal
experiments and literature review, the damage of these three odorants to
the human body can be ignored19-21.