Steam distillation methods

Onuska and Terry [14] have described a method for the determination of chlorinated benzenes in bottom sediment deposits. Sample preparation methods using Soxhlet extraction, ultrasonic extraction or steam distillation were compared. The chlorinated benzenes were characterized by open tubular column gas chromatography with electron capture detection. In recovery studies using sediments with different organic matter contents, the steam distillation method was the most efficient. Detection limits were in the range 0.4-10pg kgy1. 

Clean-up after steam distillation is usually performed by alumina [31-33] or silica [2], Sweetman reported a method without any clean-up at all [34]. The steam distillation method has only been applied to the alkylphenols and short-chain ethoxylates, because of the poor volatility of longer chain ethoxylates. 

Bremner, J.M. and Keeney, D.R. (1965) Steam distillation methods for determination of ammonium, nitrate and nitrite. Analytica Chimica Acta 32, 485 95. 

A 10 gram sample was placed in a 200 ml round bottom flask and 100 ml of distilled water added. A Dean-Stark trap and condenser were used and the mixture was brought to a boil. The steam distilled oil was measured after four hours versus control mixtures. In order to measure surface oil on the spray-dried powders, the powder was first washed with a solvent (ethyl ether or hexane) then oil retentions were run by the steam distillation method illustrated above. Differences in oil volume for solvent washed versus non-washed were attributed to surface oil on the spray-dried powders. 

Ajowan oil is extracted from the seed by the steam distillation method. The two kinds of oils, i.e. essential oil (volatile oil) and non-volatile fatty oils, are extracted. Two... 

Failure of aliphatic aldehydes to be produced in high yields by application of this steam distillation method to estragole and 1-dodecene may be attributed to the increased stability of the intermediate hydroperoxides toward hydrolysis. In other words, the conversion rates of the corresponding intermediates, V to VI to VII, are so slow that the hydroperoxides are either steam distilled and/or undergo the relatively more rapid oxidative rearrangement to VIII and subsequent conversion to IX. 

The advantage of steam distillation over other methods of volatile oil extraction lies principally in its wide applicability and speed of operation. Most plants or plant parts, with the exception of the flowers in some few cases, may be extracted most readily and most expeditiously and with a minimum amount of labor by the steam distillation method. The simplicity of the operation is obvious. The removal of the oil is much more complete than by any other process. Furthermore, there is produced as a by-product during the distillation an aqueous distillate which is completely saturated with the oil. The aqueous distillate may in many instances be utilized and sold as an aromatic water of commerce, especially in such cases as lavender, orange flowers, rose, etc. The aromatic waters possess excellent odors, largely because of the extreme dilution of the odorous compounds held in solution, and are useful in the perfumery and toilet-preparation industries. When the aqueous distillate from the plant has no marketable value, it may be profitably collected and returned to the boiler. In case of a further distillation of the same plant it will materially add to the yield of oil, since the distillate is a saturated solution of the oil. Many oils are extremely soluble in water. Distillates from oils of this class usually augment considerably the yield of oil when returned to the boiler and transformed into steam and oil vapors. 

When the major alkaloid in tobacco samples is nor-nicotine, the commonly used steam-distillation method and automated procedures result in poor estimates of nicotine and nornicotine. Rosa18 therefore developed a pyrolysis-gas chromatographic method, whereby pyrolysis was carried out with a Victoreen pyrolyzer fitted to the gas chromatograph. Nicotine is relatively volatile and readily released by pyrolysis, even at 100°C. Nornicotine, being less volatile, showed maximum release by pyrolysis at 300°C. The pyrolysis-gas chromatography was carried out with ca. 1 mg of tobacco. The results obtained with the method are presented in Figure 5.3. 

There is a steam distillation method which is technically advanced to the two above methods. The steam passes through the plant and so facilitates diffusion. This, however, leads to problems if the moisture in the plant material evaporates before the oil is fully released. 

A complete steam distillation method, which modified earlier distillation apparatus, was semi-automated by Griffith and Jeffrey (1948) and Griffith... 

The variability of the composition of an EO is also impacted by the choice of the method of extraction of EOs. One characteristic of EOs is the volatility of their compounds which allows them to be easily extracted by water vapors, in contrast to fixed lipid oils and essences (concrete, absolute, oleoresins, and resinoids) which are extracted by solvents and alcohol. Guenther [9] distinguished three kinds of water and steam distillation methods for obtaining essential oils. These methods are far more restrictive than more recent extraction and separation methods which are mentioned in the European Pharmacopoeia [10] using supercritical fluids, steam distillation, dry distillation, or mechanical cold pressing of plants. 

Steam distillation may be accomplished in several ways. The product may simply be put in a rotary evaporator (if liquid, or initially slurried in water if solid) and a distillate collected. This distillate would be solvent extracted to yield an aroma isolate suitable for GC analysis. The most common steam distillation method employs Simultaneous Distillation/Extraction (SDE may be called a Likens-Nickerson method). This is one of the oldest and most popular methods for obtaining aroma isolates. Chaintreau [31] has provided a very good review of this method and its evolution. An atmospheric pressure system is shown in Figure 3.4 (bottom). Vacuum systems must have joints that are air-tight, and all parts of the apparatus must be under rigid temperature control. 

Volatile oil content. Steam distillation method or organic solvent method. Microbiological examination. Total plate count, conforms, salmonella, molds, and yeasts. 

Hydrodiffusion is a steam distillation method, whereby steam is fed to the plant material from the top. Steam penetrating the plant matrix condenses and forces the essential oil to diffuse to the surface. Because of gravity, oil leaves the vessel together with the condensate water from the bottom of the still. Powdering the material results in better oil yields. This technique is suitable both for superficial and subcutaneous oils. The disadvantage of this technique is the undesired extraction of coumarins, psoralens, and chlorophyll into the oil. Therefore, hydrodiffusion has not become a widely used distillation technique. 

Hydrocarbon solvents, like hexane, petroleum ether, methanol or ethanol, are added to the plant or animal material in order to extract the delicate fragrance substances. The extraction by means of Soxhlet manifolds could, in some cases, facilitate the extraction procedure. After distillation to remove the solvent, the remaining extract is known as conaete. This extract can be used as such, or cold ethanol may be added to re-extract oils or fats in order to purify the extract. After ethanol evaporation, the resulting oils are more purified, and the extract is known as absolute, which is the purest and most concentrated form of essential oil. This method is useful for fragrance chemicals which are thermolabile and/or have too high a boiling point to be extracted by the steam distillation method. 

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