## 3 Results and Discussion  
### Visible Inspection of the Raman and SORS Spectra  
There is increasing interest in methodologies that allow for rapid detection of food adulteration, and these methods would ideally be portable so that these 'capable guardians' can be used directly within the food chain [40]. During the past two decades, the application of handheld Raman spectroscopy has attracted a lot of attention. In the present study we have employed three handheld Raman instruments to investigate whether it is possible to develop models that allow for the quantification of specific adulterants in EVOO. These three handheld instruments were intentionally selected as they are equipped with three different laser wavelengths at 785, 830 and 1064 nm in the near infrared (NIR) region, and thus any potential fluorescence interference should be minimal. Indeed, we found no broad spectral features that may be due to fluorescence. In addition, three adulterants were used in this study as these provide varying degrees of difference in chemical composition when compared to EVOO. Sunflower oil was expected to be the easiest to detect, followed by pomace oil (a solvent extract from the olive pulp after the generation of EVOO), and finally refined olive oil (a virgin oil that has been refined without alteration of the oil's glyceridic structure), which is thus chemically very similar to EVOO.  
Figure 2 shows representative Raman spectra of EVOO, pomace OO, refined OO and sunflower oil collected directly through a commercially available olive oil bottle using a SORS instrument with excitation at 830 nm. The mixtures of sunflower oil with EVOO have been conducted at two different volumes of oil samples in order to test whether the volume of oil inside the container made any difference. These two oils were chosen as they were in abundant supply, unlike pomace OO and refined OO, and shall be discussed below to establish that using lower volumes (28 mL) provided very similar quantitative models to those generated using a larger volume (90 mL).  
Inspection of the Raman spectra from all oils (conventional Raman (Figure S2) and SORS (Figure 2)) showed very similar features, with only subtle quantitative differences between them. However, the mixture of sunflower oil with EVOO displayed higher levels of a peak at 920 cm\({}^{-1}\) which clearly originated from components in the sunflower oil (assigned to C-H bending from lipids). This and the assignments of the main Raman active vibrations are also highlighted in Figure 2. When all the spectra were viewed (Figure S3), increasing levels of sunflower oil in the mixtures resulted in an increase in the intensity of two strong peaks at 1265 cm\({}^{-1}\) (C-H deformation) and 1657 cm\({}^{-1}\) (C=C stretch), corresponding to changes in unsaturated fatty acid composition, and decreasing in the intensity of peaks at 1300 and 1441 cm\({}^{-1}\)[42], which were also seen in PCA loadingsplots (Figure S4). In the mixtures of EVOO and pomace OO and refined OO, the story is similar but the changes in peak intensities are much smaller, which is reasonable due to these olive oils having very similar chemical composition to EVOO, as they are also derived from olives [42].