When sonicating a sample, it is important to choose the right size of probe. Each probe includes a recommended sample volume range, which can overlap with other probes. For instance, a probe measuring ½” in size will be able to process 20-250 ml.
The sample volume that needs to be processed must match with the tip diameter. One can process less than 20 ml or over 250 ml, depending on the type of sample used.
Based on the size and shape of the vessel, the ½” probe may be difficult to fit within a 20 ml volume. Here, a ¼”microtip could provide a better option. To this end, a number of factors must be taken into account when choosing the right probe for a particular application.
In case of small volumes, a small tip is needed to accommodate inside the sample tube. For processing samples inside tiny, thin vessels or for samples not more than 50 ml, small tips or Microtips are recommended.
High intensity Microtips are made for short processing times. If the tips are used for long time periods, they will produce a large amount of heat. To overcome this, Microtips should be utilized in pulse mode to bring down heat buildup.
For effective processing, a larger probe is required for larger volumes. Using a probe of appropriate size will reduce the processing time and also extend the life of the probe. In addition, using a stir bar can help in processing large samples.
Table 1. Tip diameter and processing volume range
||Processing Volume Range
||200ul - 2ml
||200ul - 2ml
||500ul - 15ml
||5ml - 50ml
||20ml - 250ml
||100ml - 500ml
||200ml - 1,000ml
|1” with booster
||500ml - 1,500ml
Aqueous Samples vs. Solvents
For aqueous samples, a replaceable tip probe is recommended as these probes have threaded ends and can be easily replaced when the tip is worn out. When sonicating a solvent-based solution, the liquid tends to enter into this threaded tip. Presence of liquid inside the tip will overload the sonicator or display an error message.
When processing low surface tension liquids, like acetone and acetone, or a sample containing solvents, a solid tip probe should be used. However, when the tip fails to sonicate effectively, the probe must be replaced.
An example of solid probes is a sapphire tip probe which has a sapphire disk attached to the end. Sapphire tips are long-lasting when compared to titanium tips. Also, only small quantities of the sapphire material are released into the sample. However, a sapphire tip can only be utilized with aqueous samples.
Solvents tend to separate the sapphire tip from the probe and hence sapphire tips must be used for processing abrasive samples where normal tips are not suitable or in those applications where titanium contamination is not desired.
Shape and Size of Vessel
The ultrasonic energy is produced from the tip and is directed downward. When a sample is being processed, the liquid is pushed in all directions. In case the vessel is too wide, it will not mix properly and some amount of sample will remain untreated.
On the other hand, when the vessel is narrow the time taken to process the sample is reduced significantly. Therefore, a narrow vessel is generally preferred to a wide vessel.
Foaming usually occurs with sample volumes of less than 1 ml. Two issues can cause foaming: either the tip is not immersed deep enough or the amplitude setting is too high. Certain samples foam quite easily, but a Cup horn will not produce foam.
Another important issue is the depth of the probe within the sample vessel. In case the probe is very close to the liquid’s surface, it will produce foam. Likewise, if the probe is too deep, it may sonicate against the vessel’s bottom and will not process the sample effectively. For effective mixing, the sample must flow freely beneath the tip.
In addition, prior to processing the samples, the probe must be tested in a vessel filled with water to observe the flow pattern of the liquid and also the ultrasonic energy. During this test, the probe’s depth can be adjusted until sufficient mixing and movement of the water is seen.
A booster horn can increase the intensity of a 1” or ¾” probe, but this device cannot be used for smaller diameter probes as they already provide high intensity. The booster can be used for processing complex samples with volumes over 500 ml.
Amplitude vs. intensity
Amplitude and intensity have a direct relationship. When users operate at a low amplitude setting, they will deliver low intensity sonication and vice versa.
In order to reproduce results, parameters such as amplitude setting, viscosity, temperature, and sample volume should remain consistent. Amplitude is the most important factor when reproducing sonication results.
During sonication, small fluctuation in the wattage display is normal. However, major fluctuations in wattage (+/-20 W) may signify a problem with the sonicator, sample, or setup.
Qsonica designs, develops and manufactures the world's most technologically advanced ultrasonic liquid processors. Our 40 years of experience in a wide range of industries has enabled us to develop a full line of equipment and accessories to provide solutions for the following applications:
- Cell Disruption
- Nanoparticle Dispersion
- Creating Emulsions
- Shearing DNA
- ChIP Assay
This information has been sourced, reviewed and adapted from materials provided by Qsonica - Ultrasonic Liquid Processors.
For more information on this source, please visit Qsonica - Ultrasonic Liquid Processors.