Supplementary Section: Purity Analysis of Adulterated Essential Oils by FT-IR Spectroscopy and Partial-Least-Squares Regression

The peppermint oil results are presented in this supplementary section. This section includes Figures 1–4 and Table I. 

Figure 1 (web): FT-IR spectra of calibration samples of (a, left) WO, (b, left) TTO, (c, left) RO, and (d, left) LEO. Cross sections of FT-IR spectra of (a, right) WO, (b, right) TTO, (c, right) RO, and (d, right) LEO adulterated with peppermint oil. (Peppermint oil adulteration ranged between 1% and 90% [wt/wt].)

Figure 2 (web): Typical score plot of PLS-1 regression of WO adulterated with peppermint oil.

Figure 3 (web): FT-IR spectra of independent validation samples of (a) WO, (b) TTO, (c) RO, and (d) LEO adulterated with with peppermint oil.

Figure 4 (web): Plots of actual and determined percent composition of independent validation samples of (a) WO, (b) TTO, (c) RO, and (d) LEO adulterated with peppermint oil.