2.5. Limonene measurement

Limonene dissolved in the isopropyl myristate (IM) overlay was used for quantification. The samples were prepared by diluting 100 ​μL of the IM overlay in 300 ​μL of pure IM, and limonene concentration was quantified using a gas chromatography instrument equipped with a flame ionization detector (Hewlett-Packard model 7890 A, Agilent Technologies, CA, USA) and a 30-meter DB5-MS column (J&W Scientific). The oven temperature initiated at 70 ​°C and held for 3 minutes, followed by an increase at 5 ​°C/min to 260 ​°C and held for 3 minutes. Limonene was quantified by comparing peak area to that of a (R)-limonene internal standard.