The essential oil chemist works in a highly specialized field requiring careful analytical ability, ingenuity, and a highly developed sense of smell and taste. He must always be on the alert for known acjulterants and impurities and for new and hitherto untried adulterants. Above all, he must have sufficient chemical background and experience to be able to interpret the results of his analyses.
Crude adulteration of oils has lessened considerably, because of careful analytical control. Seldom does one encounter today the adulteration of lemon oil with turpentine, or the addition of acetanalide to vanillin. However, some adulterations are still in evidence, especially where strict analytical control is not maintained by government agencies and buyers. For example, at a comparatively recent date, the orange oils of French Guinea were so badly adulterated with kerosene and mineral oil fractions that the reputation of this oil suffered; government control entirely chocked this gross adulteration. Ceylon citronella oils have been adulterated with mineral oil fractions for so long that the trade has almost accepted this as a necessary evil, trying to limit the amount of adulteration rather than to stop it altogether. Such crude adulterations usually offer no problem to the esential oil chemist. A routine analysis easily discloses such falsifying.
A much more dangerous and common type of adulteration is the addition of materials that do not materially affect the physicochomical properties of an oil. Often materials are added that arc normal constituents of the oil: materials that are obtained as by-products, isolates from other oils, or synthetics. Such "sophistication" is much more difficult to detect and often may be suspected but proved only with great difficulty at best.
It is in cases such as these that a well-developed sense of smell and taste proves of immense value. Here it is important for the chemist to know what adulterants to expect. Organoleptic tests, in conjunction with physicochemical analyses, also are of great importance in evaluating the quality of unadulterated oils.
A discussion of the general procedure to be followed in examining an essential oil, isolate, or synthetic may prove of value.
A study of the odor, and in some cases the flavor, helps materially in detecting adulteration or "sophistication," and in judging quality. Comparison should be made with an oil of high quality, a "type" oil of known purity. A drop or two of the oil in question is placed upon a strip of blotting paper ; the same amount of the pure "type" oil is placed upon a second strip; and the two held together at right angles by means of a clip.1 The odor of the two oils should be studied carefully and compared at intervals. When first on blotters, addition of the more volatile adulterants is often discovered. Solvent "by-notes" may also be detected in the case of a product obtained by extraction. When the blotters have dried considerably, addition of the less volatile adulterants may often be detected materials such as cedarwood and heavy camphor oil. The study of the odor and flavor often suggests the presence of adulterants which may be confirmed by special chemical or physical tests. Or adulterants indicated by the analysis may be confirmed by a study of the odor and flavor. Moreover, organoleptic tests are probably the only satisfactory method, thus far developed, of detecting burnt, pyroligneous "by-notes" resulting from improper distillation, and of detecting slight spoilage in certain oils, as for example the citrus oils.
1 The wooden clips sold for drying photographic negatives prove very satisfactory.

Also of great importance is the determination of the physical and chemical properties of a given oil. The specific gravity, the optical rotation, the solubility in dilute alcohol, and the refractive index should be determined for all oils and liquid isolates and synthetics as a matter of routine. Other special tests are also to be carried out, depending upon the material under consideration (e.g., ester content, total alcohol determination, congealing point, evaporation residue). For an optically inactive, crystalline solid, the best criterion of purity lies in the determination of the melting point.
Comparing these analytical figures with results of previous analyses and with data published in the literature, the chemist may obtain an indication of the purity and quality of the oil. Crude adulteration often is discovered at this point.
The relationship between the individual chemical and physical properties is often very revealing. Thus, the addition of orange terpenes to an orange oil will cause a lowering of the specific gravity, refractive index, and the evaporation residue, and a corresponding increase in the optical rotation; the addition of turpentine oil will cause a lowering of the optical rotation as well as of the othor three properties.
Another factor to be considered is possible sources of adulteration or contamination. Benzaldehyde should be tested for chlorine, since a positive halogen test would indicate manufacture from benzyl chloride or insufficient purification. Low refractive index and specific gravity of a linaloe oil suggest adulteration with ethyl alcohol, a common form of adulteration for this oil.
The value of the relationship between each physical and chemical property, and between the analysis and the odor and flavor cannot be stressed too strongly.
The analytical figures obtained in as complex a material as an essential oil seldom represent actual percentages of single constituents. Thus, in the case of an ester determination, all saponifiable material is calculated as a certain ester, regardless of the fact that itnquestionably other esters are present or that other constituents are capable of saponification. The figures obtained, however, are no less valuable for practical purposes. Nevertheless, it may be seen that in this field of chemistry it is of utmost importance that a procedure be rigidly followed in order to assure reproducible results that are of practical value.
The main purpose of the following discussion is to help standardize such analytical procedures so that chemists throughout the essential oil industry may obtain results that can be reproduced by other workers in this field as well as by chemists in related industries.

comment 0 nhận xét:

Post a Comment

© Pharmacognosy | Plants | herbal | herb | traditional medicine | alternative | Botany | © Copyright 2012 ; Email: