Ultrasonic disruptors

An alternative extraction technique is sonication of the soil with an ultrasonic probe. The technique is relatively quick, but its speed is limited by the sequential nature of sample processing. Samples are placed in a glass extraction vessel and mixed with a drying agent (anhydrous sodium sulphate) until free flowing. Solvent is added and the ultrasonic disruptor is placed in the solvent and above the sample for a period of 3 min. The solvent is decanted, fresh solvent is added to the sample, and the process is repeated twice more. The extracts are combined and concentrated for further processing (cleanup). 

There is on record at least one investigation leading to the emulsion synthesis of YBa2Cu307 x powders [207]. The basic solvent system was Tween 85, poly(oxyethylene) sorbitan ester/kerosene (oil phase). The aqueous phase containing dissolved salts Ba(N03)2, Cu(N03)2.3H20 and Y(N03)3.H20 in proper proportions was added into the surfactant/oil system under stirring which was continued for several hours after the addition was complete. An ultrasonic disruptor was used for decreasing the aqueous droplet size. This emulsion was added drop by drop into hot (180"C) kerosene. The product powders were washed with toluene... 

Frequency and Intensity. Most ultrasonic baths operate in the 30 -80 kHz range. Frequency is rarely an important factor, provided the frequency is low enough to permit cavitation. The cell disruptors normally adapted for sonochemical uses operate at 20 kHz. The intensity must be enough to produce cavitation. Beyond that, optimum intensities for heterogeneous reactions have not been determined. 

Review.1 This review includes a discussion of the three types of ultrasonic generators whistlers, cleaning baths, and probe disruptors. The last is the most efficient, but the most expensive. Cleaning baths are inexpensive, but are limited in the temperature range to that of the liquid used, generally water. The review concludes that sonication is most useful in heterogeneous reactions, particularly those of organometallics. The references (235) date from 1953 to the present time, with most in the last 10 years. 

RiZn. Dialkylzinc reagents can be prepared from an organic halide, lithium wire, and zinc bromide at 0° in toluene-THF by sonication in a cell-disruptor generator. Yields are essentially quantitative. Diarylzinc reagents and dimethylzinc can be prepared by sonication in an ultrasonic laboratory cleaner. 

Figure 10-3. Sonicator or sonic cell disruptor showing the sonic wave generator in the background and the titanium transducing element in the foreground. Needle tips capable of operating in small test tubes may be interchanged with the larger tip (arrow) shown here. (Courtesy of Heat Systems-Ultrasonics, Inc., Plainview, N.Y.)...

Fisher Scientific) was emulsified into aqueous soap solutions of 0.25 w% each of sodium laurate and sodium oleate prepared from sodium hydroxide, lauric acid (Aldrich Gold Label) and oleic acid (Fisher Purified). Coarse emulsions were used for microscopy (as in Figure 2), but fine emulsions (with droplet sizes of about 0.2 microns), used for determination of middle phase film thicknesses, were made by ultrasonication with a cell disruptor. 

One of the original uses of power ultrasound in biochemistry was to break down biological cell walls to liberate the contents (indeed many ultrasonic horn systems were first marketed as cell disruptors). Subsequently it has been shown that power ultrasound can also be used to produce a positive effect on enzyme activity. If the intensity is too high however the enzymes can be denatured. 

The aliquot designated for extraction at neutral pH was extracted three times, with fresh 100-mL acetone/hexane (50/50). An ultrasonic cell disruptor, in pulsed mode at 50 percent duty cycle, was employed to enhance the contact between the extraction solvent and soil. Following each extraction, the soil was allowed to settle, the solvent decanted, and the combined supernatants from the neutral pH extraction were dried through a column of anhydrous sodium sulfate (5-cm bed height 3-cm diameter). Concentration of the extract was performed using a Kuderna-Danish evaporator. Final volume was adjusted to 1 mL using nitrogen blowdown evaporation. 

The mixing for W/O emulsions is usually performed in the laboratory by simple equipment like a magnetic stirrer, an ordinary mechanical stirrer with multiple fins, a planetary stirrer, a high shear / high speed blender, an ultrasonic vibrator or in some cases a sonic disruptor [18]. Ordinary rotational mixing can be coupled with sonication for obtaining relatively small droplets [42]. 

For the protein nanocomposite formulation, 400 g of water and 400 g of glycerol were also blended in a large beaker with a mechanical stirring device for two minutes, prior to the addition of 60 g of Cloisite Na. For the untreated system the mixture was then eombined drip-wise with 1200 g of the soy protein using a ten-litre laboratory seale high-speed mixer (HSM-10) for five minutes prior to extrusion similar to the neat protein film. For the ultrasonically treated system the mixture was treated with a point souree ultrasonic device (Branson sonifier model 250 W cell disruptor) for one hour in an iee-eooled environment (as outlined in section 11.2). This mixture was then eombined drip-wise to 1200 g of the soy protein using a ten-litre laboratory seale high-speed mixer (HSM-10) for five minutes prior to extrusion similar to the neat protein film. 

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