Choosing the right homogenizer horn is an important step in most ultrasonic homogenization applications. Also known as a probe, the horn is inserted into the sample and vibrates rapidly. This transfers ultrasonic energy to the sample; specifically, the particles in close proximity to the horn are blasted with huge amounts of energy.
The energy blast, and the vacuum formed each time the probe retracts during its vibrational movement, causes the formation and collapse of bubbles in the surrounding liquid, a process known as cavitation. Cavitation creates shear and shock waves, which facilitate a range of applications including cell disruption, particle size reduction, emulsification, and dispersion.
There are a variety of probe types available, ranging in size, shape, and function. Here, we look at the main factors to consider when deciding which horn is right for your application and the different types of probes available.
There are a surprising number of options available with several factors affecting your decision, including:
- Vessel type
- Sample size
- Amplitude and intensity
Let’s look at each of these in detail:
Certain applications call for a special shape of horn. For example, cup horns are used to indirectly homogenize samples enclosed in sealed microtubes, which keep samples cool. These are generally used in situations where the sample volume may be too low for direct probe sonication, where lower-intensity or more diffuse ultrasonic energy is helpful.
In other cases, a flow horn may be suitable. These enable you to process a semi-continuous stream of samples and may be water-jacketed to assist in cooling. These are used when an in-line process is preferable or when you want to exceed the batch processing capacity of your ultrasonic homogenizer.
Some applications require the homogenization of samples that contain gritty solids. This could lead to extensive wear and pitting of the tip of the horn, lowering its effectiveness in homogenization as well as its useful life. To maintain homogenization efficiency and help avoid costs associated with regularly replacing the horn, you can look for probes with replaceable tips. The Standard Probes for the Q500 and Q700 Sonicators come with replaceable or solid tips, but note that replaceable tips can’t be used with organic solvents.
Have a high throughput application? There are horns specifically designed for those cases too.
Dual, 4-tip, and 24-tip horns for the Q500 & Q700 Sonicator.
2. Vessel Type
You may find that it’s difficult to find a probe that fits your desired vessel type. There are some solutions in this regard too.
Have a long-necked vessel? You may need to use a probe extender. For example, these extenders for Q500 and Q700 Sonicators enable you to use standard probes in long-necked vessels.
If your vessel has a small diameter, the Microtips for Sonifier® S-250/450 and SFX250/550 could be a good fit.
Generally, however, your choice of vessel should accommodate your homogenization process. As the ultrasonic energy is released downwards from the probe, you should use a vessel in which your liquid will be deeper than it is wide and place the tip of your probe somewhat close to the surface of the liquid while ensuring it is never run in air.
3. Sample Size
Most ultrasonic homogenizers are compatible with a standard set of probes that come in a variety of sizes, with specifications focusing on the tip diameter of the horn. When choosing a size, one of the first things you need to look at is your sample size to make sure your probe is compatible.
These specifications for standard Q55 Sonicator tips indicate the range of processing volumes each is suitable for:
Microtip Probes for the Q500 & Q700 Sonicators are specially designed for use with small samples and provide high intensity (more on that in the next section).
4. Amplitude and Intensity
An additional consideration is the maximum amplitude you can reach with a given probe, which is determined by its size. As the probe size increases, the wattage you need to maintain a given amplitude will also increase. For this reason, the maximum amplitude of a probe will decrease as you go up in probe size.
The effectiveness of sonication is impacted by the intensity of cavitation which is determined by the amplitude. The higher the amplitude, the higher the intensity of sonication.
If you already have a standard horn, an alternative to a high-gain horn is to attach a booster to your existing probe. A booster attaches between the converter and the horn and increases the intensity. Examples include the Qsonica 2:1 Titanium Booster Horn and the Branson Boosters for the Q500 & Q700 Sonicators.