Technique of steam distillation

The student should be familiar with the theory of steam distillation, given in Section 1,6, before carrying out the operation in the laboratory. 

To carry out a steam distillation, the solution (or mixture or the solid with a little water) is placed in the flask B, and the apparatus is com-pletely assembled. Steam is passed into the flask B, which is itself heated by means of a small flame to prevent too rapid an accumulation of water, at such a rate that it is completely condensed by the condenser C. The passage of steam is continued until there is no appreciable amount of water-insoluble material in the distillate. If the substance crystallises 

It is frequently convenient to carry out the steam distillation from the flask in which the chemical reaction has taken place losses due to 

The set-up of Fig. II, 41, 3 ensures the complete condensation of the steam when a rapid flow of steam is necessary for satisfactory results, and is useful in the distillation of large volumes of liquids of low vapour pressure, such as nitrobenzene. Thus the flask A containing the mixture may be of 3-litre capacity and B may be a 1-litre flask the latter is cooled by a stream of water, which is collected in a funnel and conducted to the sink. The receiver C must be of proportionate size all stoppers 

Sometimes an air bubble enters the tube E and prevents the regular flow of liquid from B the air bubble is easily removed by shaking the rubber tube. The flask A is heated (e.g., by a ring burner) so that distillation proceeds at a rapid rate the process is a continuous one. If the liquid to be steam distilled is lighter than water, the receiver must be modified so that the aqueous liquors are drawn off from the bottom (see Continuous pjg, jjt 5 Extraction of Liquids, Section 11,44). 

The rubber tube E for the returning aqueous liquor must at some point be lower than the entrance to the tube C so that a trap of liquid will be formed and prevent the vapours from A entering the side tube. 

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The technique of steam distillation is sometimes used in purification because it is fairly selective in that relatively few water-insoluble substances are steam-volatile, and because it facilitates the distillation of some compounds at temperatures well below their normal boiling points. The codistilled water is usually easily removed. Examples of its use include the distillation of nitrobenzene and naphthalene. 

Purpose To isolate the natural product citral using the technique of steam distillation. 

Figure 10 shows a series of three distillation apparatuses used for routine analysis. Figure 11 describes the construction of the distilling head and demonstrates the technique of steam distillation from a solution at a constant temperature above 100°C. 

Considerable effort has been made to examine the volatiles and trace components that contribute to food flavors. Sone early techniques for measuring the volatile components in food products by gas chromatography consisted of analyzing headspace vapors to detect vegetable and fruit aromas (5) and volatiles associated with other food materials ( ). AlTo, sample enrichment has been used in the analysis of Tome food products. However, these techniques require steam distillation or extraction and concentration, or both, before the volatile mixture can be introduced into a gas chromatograph (, 9, 10). Besides being... 

It has been known for centuries that codistillation of many plant materials with steam, a technique called steam distillation, produces a fragrant mixture of liquids called plant essential oils. For thousands of years, such... 

The harshest technique is steam distillation, which involves boiling garlic followed by extracting compounds from condensed steam. Steam-distilled garlic oils consist of the diallyl (57%), allyl methyl (37%) and dimethyl (6%) mono- to hexasulfides. These oils are diluted (>99%) with vegetable oils to obtain a practical-sized pill and to stabilize the sulfides (Lawson, 1993). 

Hydrodiffusion is a relatively new technique. It is essentially a form of steam distillation. However, it is steam distillation carried out upside down since the steam is introduced at the top of the pot and the water and oil taken off as liquids at the bottom. The plant materials diffuse through the cell membranes into the steam and are carried to the bottom of the still by the descending flow of condensate. This technique therefore saves energy because it is not necessary to vaporise the oil. 

Benzoic acid and its salts may be determined by titration with sodium hydroxide after extraction of the benzoic acid from an aqueous food suspension into chloroform, and evaporation of the chloroform and any acetic acid present (AOAC method 963.19). Vanillin interferes with this determination and a more selective method involves the determination of benzoic acid in an ether extract by UV absorption at 272 nm, as described in AOAC method 960.38. An alternative method of isolating benzoic acid from food involves the use of steam distillation and TLC separation. These sample preparation techniques are used in AOAC method 967.15 prior to the determination of benzoic acid by UV absorption. 

Purpose. In this exercise you will extract oil of cinnamon from a native plant source, such as Cinnamomum zeylanicum, and then purify the principal flavor and odor component of the oil, cinnamaldehyde. The experiment demonstrates the importance of steam distillation techniques (at the semimicro level) [Pg.239]

Steam Distillation. The process of steam distillation can be a valuable technique in the laboratory for the separation of thermally labile, high-boiling substances from relatively nonvolatile materials. For steam distillation to be... 

This technique involves steam distillation along with solvent extraction for the isolation of essential oils from plants. This technique has been applied extensively as a step prior to compositional studies of essential oils, sueh as eurcuma [32], marjoram [33], grapes [34], soybeans [35], and lavender [36],... 

Steam distillation Vacuum or steam distillation is a technique feasible for methylmercury extraction because of the relative volatility of methylmercury hydrides.The strong point of this technique is that efficient matrix separation is achieved, which is particularly important when analysing waters rich in organic matter. A detailed description of steam distillation for methylmercury analysis was published by Horvat, and recently an improved apparatus was introduced by Hintelmann. ... 

The most popular device for fluoride analysis is the ion-selective electrode (see Electro analytical techniques). Analysis usiag the electrode is rapid and this is especially useful for dilute solutions and water analysis. Because the electrode responds only to free fluoride ion, care must be taken to convert complexed fluoride ions to free fluoride to obtain the total fluoride value (8). The fluoride electrode also can be used as an end poiat detector ia titration of fluoride usiag lanthanum nitrate [10099-59-9]. Often volumetric analysis by titration with thorium nitrate [13823-29-5] or lanthanum nitrate is the method of choice. The fluoride is preferably steam distilled from perchloric or sulfuric acid to prevent iaterference (9,10). Fusion with a sodium carbonate—sodium hydroxide mixture or sodium maybe required if the samples are covalent or iasoluble. 

The concern by consumers about cholesterol has stimulated the development of methods for its removal. Three principal approaches are in the pilot-plant stages use of enzymes, supercritical fluid extraction, and steam distillation. Using known techniques, it is not possible to remove all cholesterol from milk. Therefore, FDA guidelines identify cholesterol-free foods as containing less than 2 mg cholesterol per serving, and low cholesterol foods as containing from 2 to 20 mg (37). 

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

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