Tips to Increase Effectiveness of Ultrasonic Liquid Processing

Ultrasonic probe sonicators are a versatile set of equipment having applications in fields as diverse as nanotechnology, food processing, microbiology, and pharmaceutical research. Amongst other applications, ultrasonicator systems are used for cell disruption, dispersion, atomization, homogenization, and emulsification.

Three components form the heart of an ultrasonic sonication system: the ultrasonic generator converts, the piezoelectric converter, and the horn/probe assembly. The generator transforms low-frequency voltage into high-frequency voltage (20 kHz). The converter then converts electrical energy delivered from the generator into mechanical vibrations (20 kHz). Finally, the horn/tip assemble receive high-frequency vibrations from the converter and amplify these whilst transmitting them into the sample been processed. The intense vibration of the probe tip inside the liquid forms a cavitation zone that causes bubbles to implode and release tremendous amount of energy.

As a result, the sample within the cavitation zone is subjected to ultrasonic processing. Ultrasonic liquid processing depends on a lot of variables, including sample volume to be processed, the viscosity of the material to be processed, the type of horn used, and the diameter of the probe tip. Given below are some general tips to follow in order to increase the effectiveness of liquid processing using ultrasonicator systems:

1. Submerge probe tip appropriately in the sample

It is extremely important to ensure that the probe tip is properly immersed in the liquid being processed. Keeping it above the half-way mark of the vessel will lead to foaming or bubbling. On the other hand, if it is submerged too low, the circulation rate will be affected. In both cases, the quality of sonication will be poor. When sonicating small samples, it is preferable to use cup horn assembly to avoid foaming.

2. Use solid probe tips for organic liquids

Whilst replaceable probe tips (with threaded ends) have a flexibility to be removed, they are not as effective when processing organic liquids. This is because during sonication such liquids can seep into the tip and loosen thereby overloading the system. Thus, solid probe tips are preferable for processing such liquids to avoid overloading and maintaining consistency in sample reproducibility.

3. Use narrow vessel for uniform processing

Since the ultrasonic energy is generated from the tip and is directed downward into the liquid in all directions, a narrow vessel produces uniform and quicker results than using a wide vessel. When a wide vessel is used, the sample at the lateral ends of that vessel is rarely affected by the cavitation zone at the centre. This leads to poor sonication results. In addition to this, using a narrow vessel causes faster ultrasonic cycles than using a wider vessel.

4. Ensure probe size matches recommended sample volume range

The size of the probe is directly proportional to the volume of sample to be processed. For instance, large sample volumes require a large-size probe for ideal processing. When we use a probe tip which is smaller than ideal increases the sonication time as well as decrease the life of that probe. On the contrary, when processing smaller volumes (50 ml and less), microtips are recommended. Since smaller tips deliver greater intensity, you have to take care to use the pulse mode to prevent excessive heat build-up.

Paresh Shah is a Director at Life-Care Equipments Pvt. Ltd., a leading manufacturer and distributor of a wide range of ultrasonic cleaning systems.