Essential oils quantitative analysis

NMR is not frequently used for the direct analysis of plant extracts. NMR spectroscopy, for example, is sometimes used in the identification of essential oils. Quantitative NMR procedures for the determination of constituents are rarely reported but... 

Shaw, P. E. Review of quantitative analysis of citrus essential oils. J. Agric. Food Chem, 1979, 2], 246-257. 

Quantitative chromatographic analysis of the composition of distilled essential oil was reported previously by Nigam and Purohit (1960) and by Lawrence (1970). The major constituent of large cardamom essential oil is 1,8-cineole (65-80%), while the content of a-terpenyl acetate is low (traces to 5%). The monoterpene hydrocarbon content is in the range of 5-7%, of which limonene, sabinene, terpinene and pinene are significant components. The terpinols comprise approximately 5-7% of the oil. The high cineole and low terpenyl acetate probably account for the very harsh aroma of this spice in comparison with that of true cardamom (Pruthi, 1993). 

For an essential oil such as lavender, the same major components will be present these are linalool, linalyl acetate and 1,8-cineole. This is the qualitative knowledge. The different types of lavender essential oils will contain different amounts of constituent compounds. Spike lavender, Lavandula latifolia, has high amounts of 1,8-cineole (25-37%), while true lavender, Lavandula angustifolia, has very small amounts (0-5%). Lavandula latifolia may contain up to 60% camphor, while Lavandula angustifolia has only up to about 12%. This is quantitative information. A quantitative analysis is needed to help identify different types of oil and can distinguish chemotypes. 

Analysis of an essential oil will tell us what compounds are present (qualitative analysis) and in what amounts (quantitative analysis). However, when considering the composition of any named oil it is difficult to lay down precise criteria. As with all products of natural origin, there will be variations according to growing conditions and how they are harvested, extracted and stored. Even if the species of plant is defined and the parts used for oil production are carefully controlled, variation in composition will occur. This has previously been explained in terms of chemotypes and will be examined in more detail for other essential oils later in this chapter. Even when examining a particular chemotype there will be differences in the amounts of constituents, although these are usually within a fairly narrow range. 

Analysis The identification of the composition of a substance. Physical methods used for essential oil mixtures include GC-MS. The identification of substances is called qualitative analysis, while the estimation of the amounts of components present is quantitative analysis. 

Quantitative analysis Measurement of the amounts or concentrations of components in a substance, e.g. percentage amounts of compounds in an essential oil. 

The main method of analysis of monoterpenoids in essential oils is a capillary gas chromatography. Due to the high volatility of monoterpenoids and the high speed and efficiency of the capillary gas-chromatography it is applied nowadays as the most universal method for a qualitative and quantitative analysis of monoterpenoids mixtures. 

The first raw materials for the flavour industry included extracts, tinctures, oleoresins, juice concentrates, essential oils, and a few synthetic chemicals (Tab. 3.1). Up to the 1950s, flavour research was concentrated on the isolation, stmcmral analysis, and synthesis of just a few quantitatively outstanding natural materials (Tab. 3.1). The situation changed dramatically with the advent of gas chromatography as a means of analysis, especially in conjunction with mass spectrometry. 

The percentage of essential oil content in dry chamomile flower-heads and its qualitative and quantitative characteristics, which were determined by the GC-analysis are presented in comprehensive Table 7.1. Percentage contents of the essential oil from chamomile flower anthodia were ranging 0.63 0.19 over the whole examined samples. 

NIR can also play an important role in phytoanalysis. There are some reports on the use of NIR for the quantitative analysis of water content, residual solvents of dry extracts, as well as for the analysis of constituents. It has been used in the analysis of polyphenols (wine, soy) and a quantitative NIR reflectance spectroscopy method was established for the determination of two major constituents of St John s wort (hyperforin and biapigenin) using HPLC as reference method. It was also successfully used for the rapid evaluation and quantitative analysis of essential oils using GC as reference method. It can be considered a rapid and highly effective alternative method to conventional quantitative analysis of plant extracts. 

Several attempts have also been made to obtain information about the composition of essential oils using IR spectroscopy. One of the rst comprehensive investigations of essential oils was published by Bella nato and Hidalgo (1971) in the book Infrared Analysis of Essential Oils in which the IR spectra of approximately 200 essential oils and additionally of more than 50 pure reference components have been presented. However, the main disadvantage of this method is the low sensitivity and selectivity of the method in the case of mixtures with a large number of components and, second, the unsolvable problem when attempting to quantitatively measure individual component concentrations. 

Godefroot, M., P. Sandra, and M. Verzele, 1981. New method for quantitative essential oil analysis. 

Bazina et al. (2002) stated, Hence, a simple quantitative analysis of the essential oil composition is not necessarily appropriate for estimating genetic proximity even in closely related taxa. ... 

The application of two methods, conventional (30 m x 0.25 mm ID, 0.25 pm column) and fast (10 m X 0.10 mm ID, 0.10 pm column), on ve different citrus essential oils (bergamot, mandarin, lemon, bitter oranges, and sweet oranges) has been reported [49]. The fast method allowed the separation of almost the same compounds as the conventional analysis, while quantitative data showed good reproducibility. The effectiveness of the fast GC method, through the use of narrow-bore columns, was demonstrated. An ultrafast GC lime essential oil analysis was also performed on a 5 m x 50 pm capillary column with 0.05 pm stationary phase Im thickness [50]. The total analysis time of this volatile essential oil was less than 90 s a chromatogram is presented in Figure 7.2. 

Analytical Methods. Identification of Terpenols in Essential Oils by Trifluoroacetylation and F N.m.r. Spectroscopy . Chemical Study of Trifluoroacetyl Signal in the F N.m.r. Spectra of Trifluoroacetylated Natural Products . Structure Determination of Trifluoroacetyl Steroids by F N.m.r. ." Determination of Structure and Quantitative Analyses of Hydroxy Steroids in the Microgram Range. Analysis of Hydroxy Steroids by F N.m.r. Spectroscopy . Nuclear Magnetic Resonance Studies of the Interaction of... 

Formacek, V. and K.H. Kubeczka, 1982a. Quantitative analysis of essential oils by 13C-NMR-spectroscopy. In Atherische Ole Analytik, Physiologie, Zusammensetzung, K.H. Kubeczka (ed.), 42-53. Stuttgart, New York Georg Thieme Verlag. 

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