Odour purity

The use of the sensory powers of the nose as an analytical tool is explored under odour purity in Chapter 7. It is a simple measure of quality but is subjective, as it requires insight and experience. 

Sensory analysis The odour of an essential oil can be evaluated by conducting investigations on the evaporation of an essential oil under standardized conditions and comparing this to a standard sample of the oil. This is sometimes referred to as odour purity but is a rather subjective method. It involves putting the essential oil and a standard sample onto separate smelling strips and allowing them to evaporate to a final dry-out under the same environmental conditions and time scale. This, along with a visual inspection of the oil, is the only immediate quality control measure available to the aromatherapist. 

Sample purity is always important when measuring properties for SAR work. In the field of olfaction, the organoleptic purity (i.e. odour purity) is even more important than chemical purity, especially when measuring odour character. A small trace of an impurity with a very intense odour is likely to lead to incorrect results in the odour measurement and thus render the data, and hence any resultant SAR, invalid. For example, 1 ppm of thiomethanol will distort the odour of geraniol far more than would 10% of citronellol. Therefore any SAR on odour will be suspect if the data originates from a source which is unfamiliar with measurement of organoleptic purity. 

Characteristics evaluate as appropriate under all process conditions Formula (chemical structure) Purity (identity of any contaminants), physical state, appearance, other relevant information Concentration, odour, detectable concentration, taste ... 

Aeetylene is a simple asphyxiant and anaestlietie. Pure aeetylene is a eolourless, highly flammable gas with an ethereal odour. Material of eommereial purity has an odour of garlie due to the presenee of impurities sueh as phosphine. Its physieal properties are shown in Table 9.4. Aeetylene, whieh eondenses to a white solid subliming at -83°C, is soluble in its own volume of water but highly soluble in aeetone. 

Phenyl-ethyl alcohol, or benzyl carbinol, has been known for many years, but its powerful rose odour has been entirely overlooked, its discovery having been made by an ordinary research chemist and not a perfumery expert. Its preparation was described in the Berichte (9, 373) in 1876, but the product there noted was evidently impure, as its boiling-point is recorded as 212°. Commercial specimens vary greatly in both their odour and their keeping properties, some samples deteriorating in odour very rapidly. It is, therefore, very important to -obtain it in a state of the highest purity. It has the following characters —... 

For hundreds of years the essential oil of lavender has been well appreciated for perfumery purposes [72]. Lavender oil is obtained by steam distillation from the fresh-flowering tops of Lavandula angustifolia Miller (Lavandula officinalis Chaix) [73]. It is a colourless or pale yellow, clear liquid, with a fresh, sweet, floral, herbaceous odour on a woody balsamic base [73, 74]. According to the European Pharmacopoeia, characteristic components of lavender oils are limonene, cineol, 3-octanone, camphor, linalool, linalyl acetate, terpinen-4-ol, lavandulyl acetate, lavandulol and a-terpineol. Adulterations commonly include blends of lavender oils with lavandin oil or spike oil, and the addition of synthetic linalool and linalyl acetate. In contrast, genuine lavender oils contain as main constituents (i )-linalyl acetate and (i )-linalool of high enantiomeric purity (Fig. 17.14). 

A substance is said to be chemically pure when it is made up of identical atoms and molecules. This means that the concept of purity can only apply to a single element or compound. As essential oils are made up of mixtures of organic compounds, they cannot be strictly chemically pure. Chemical purity and composition have to be related to an odour profile and be free from any contamination. Standard samples are used for reference when considering the purity of an essential oil, and the analytical techniques of GC-MS, refractive index and other methods previously described are applied. A standard sample or standard oil is a sample of a product that conforms to a specification for that product. It is kept for purposes of comparison with batch samples and used in quality evaluation. 

The range of chemicals which require some form of purification is extremely diverse. The need for chemical purification is very much a function of what the manufacturer perceives is necessary for their product, and normally reflects the wishes of the customer, product grade, application, etc. Typical improvements made include the removal of colour, and the chemical removal of minor byproducts, since the chemical manufacturer generally requires a product which has good colour, odour and purity. 

Copovidone is a product of pharmaceutical purity. It is a white or yellowish-white spray-dried powder that has a relatively fine particle size and good flow properties. It has a typical slight odour and a faint taste in aqueous solutions. 

Sensory values evaluate the olfactive purity through careful trace analysis using sniffing techniques. Determine threshold value, odour value, anosmia. 

Enantiomeric purity and enantiomeric excess (ee) are usual terms used in the determination of enantiomers. Enantiomeric purity is defined as the measured ratio (expressed as a percentage) of the detected enantiomers, whereas ee-values describe the relative difference of the separated enantiomers (expressed as a percentage). Usually quantifications are given in ee-values, but one should note, that convincing results can be concluded only for baseline-resolved enantiomers (cRs > 1.50). Exact calculations of partially resolved mirror images, as frequently happened in the current literature, remain unintelligible in view of differences in sensory qualities and odour thresholds of enantiomers Eig. 6.25, [1-9]. 

With regard to chirality evaluation as an indicator for the genuineness of natural flavourings and fragrances only chiral volatiles of high enantiomeric purity and characteristic and small ranges of ee-values should be validated in relation to their total amounts (Table 4). Furthermore, it is remarkable to pay more attention to the odour activity values (OAV) of compounds analyzed [77, 78]. 

The absolute detection threshold varies widely with chemical substances, as is shown by the large spread in odour thresholds for single compounds reported in the literature [25]. This is caused, among others, by the procedure used, the purity of the chemical substance, the equipment apphed and the sample of subjects. 

Pyridine 5 Colourless liquid flammable with characteristic nauseating odour, bp 115°C Causes puritis (itching), eczema, headache, vomitting, conjunctivitis, and abdominal pain. To be handled in a Fuming cupboard. 

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