Quantitative Analysis of Various Citrus Oils by ATR/FT-IR and NIR-FT Raman Spectroscopy

Abstract

The essential oils of various commercial citrus species were studied by ATR/FT-IR as well as NIR-FT Raman spectroscopy. Some of the most relevant monoterpene components occurring in the oil, such as limonene and γ-terpinene, show characteristic key bands in the IR and Raman spectra, which are useful for making a quantitative distinction between different oil types. Applying principal component analysis (PCA) to the spectral data, the individual citrus products are located, in most cases, as separated clusters in a 3-dimensional factor space. Cross-validation statistics showed that a partial least-square (PLS) algorithm was able to produce high quality predictions of the relative oil composition as well as general quality parameters. Both complementary spectroscopic techniques described in this study have the potential to replace existing analytical procedures because they are capable of faster quality control measurements and they allow on-line analyses during distillation or extraction processes to be performed.

Handheld Raman Spectroscopy for the Distinction of Essential Oils Used in the Cosmetics Industry

“…Considering these high contents of limonene in the essential oils of lemon and orange, it is easy to deduce that the Raman spectra of these essential oils are dominated by Raman bands of limonene. The main features in the Raman spectrum of limonene appear at 1678, 1645, 1435 and 760 cm −1 [45,46], and similar bands are clearly identifiable in the Raman spectrum of lemon and orange essential oils, as shown in Figure 1h (for bitter/sweet orange and lemon essential oils, respectively) can be attributed to a ring deformation mode of limonene.…”

Characterization of laurel fruit oil from Madeira Island, Portugal

“…Generally, vegetable oils are 95-98% fat (25,26). Subtle dissimilarities between the spectra do exist because of differences in the structure of the polymethylene chains, and considerable information can be extracted from the spectra.…”

Non-destructive NIR-FT-Raman analyses in practice. Part 1. Analyses of plants and historic textiles

“…For a large series of Raman spectra from different citrus oils we have carried out successfully a multicomponent analysis (PLS) of all relevant essential oil components. We could show that the Raman spectra can be analyzed quantitatively with very high precision and in a considerably shorter time than standard chromatographic methods such as gas chromatography [11]. It is surprising to find polyacetylenes in many plants, mainly compositae.…”

“…Furthermore, the large entrance pupil of interferometers allows short registration times. The spectra can often be evaluated quantitatively, replacing time-consuming chromatographic separation procedures [11]. The present paper demonstrates the ability of NIR-FT-Raman spectroscopy for non-destructive analysis of natural substances in plants.…”

“…Our examples demonstrate the ability of Raman spectroscopy for an easy multicomponent analysis [11]. In particular it allows us to select those parts of the plants which contain the largest concentration of the individual natural substances [17,18].…”