Best Practices for Ultrasonic Homogenization

Every ultrasonic process is slightly different. Even if what may seem like similar applications, someone else’s protocol might not work perfectly for you. You should plan on some degree of protocol optimization, but you should be able to find a good starting point for your protocol by following a few broadly applicable guidelines. Likewise, following best practices will enable you to ensure more consistent results and extend the life of your Sonicator and ultrasonic horns.

Sonication Best Practices

• Use a vessel which allows the liquid level to be deeper than it is wide. A beaker is a suitable vessel. A tray is not. Don’t take this advice to an extreme: a graduated cylinder is less suitable than a beaker.
• Ultrasonic energy is most concentrated below the tip of the ultrasonic horn, so you want ample space below the tip of the horn and the bottom of the vessel. When using a standard-sized horn (i.e. not a microtip), the tip should be placed no less than 1” below the surface of the liquid and no more than halfway between the surface of the liquid and base of the vessel. The best place to place the horn will depend on the viscosity and other properties of your liquid. The goal should be to create the best fluid flow possible.
• For large volumes (one liter or more), fluid flow may be improved by adding another source of stirring, such as a magnetic stirrer or overhead stirrer. Regardless of the stirring method used, ensure the stirrer never contacts the horn.
• Unless you have a horn which is specifically designated as handheld, the horn should be mounted to avoid it from moving around and accidentally contacting any solid surface. Mounting should be performed by clamping the converter to a stand.
• Ultrasonic homogenization will increase the temperature of the material being processed. This can be mitigated by using pulse mode, using a jacketed vessel, and / or placing your vessel in an ice bath. Certain Sonicators can be used with a temperature probe which will automatically pause the process if the temperature exceeds a user- defined limit.
• Volumes under 0.2 ml should not be processed using a probe-style horn. Use a cup horn instead.
• Processing higher viscosity liquids will generally require a longer run time and lower the maximum volume which can be processed. It may also limit the amplitude the horn can operate at, especially with larger horns.
• Amplitude is a proxy for processing intensity. Higher amplitudes may result in shorter processing times and / or smaller particle sizes (but also impart more heat).
• If you are experiencing foaming, you may need to reduce the amplitude, place the tip of the horn deeper into the liquid, or use a smaller horn.

• If you are not using a sound enclosure, always wear hearing protection when using any ultrasonic homogenizer.
• Do not run the horn in air (except when troubleshooting, and then only for a brief period of time).
• Never get the converter wet. (It can be cleaned with a damp, lint-free cloth when not in use.)
• Never allow the horn to come in contact with the sides of the vessel or any other solid object.
• Microtip horns must always be used in pulse mode.
• If you are using an organic solvent or any solvent with a low surface tension, you cannot use a horn with a replaceable tip. You must use a horn with a solid tip (which includes microtips).
• Do not use a Sonicator in explosive environments (i.e. C1D1 or C1D2).
• Gently clean the horn after each use. Running in water (or optionally, for solid-tipped horns only, in a gentle solvent such as isopropyl alcohol) is usually sufficient. If necessary, a minimally abrasive cloth or wipe can be used. Avoid wiping the tip of the horn. Horns can be autoclaved if necessary.
• If you are experiencing declining performance, you may need to replace your horn. Inspect the tip; if the tip still looks shiny, it is likely still in good condition. If it is dull and appears slightly rough, that is an indication of pitting / wear and it may need to be replaced.
• Processing suspensions of hard or abrasive solids will substantially increase the wear on your horn, requiring it to be replaced more often.
• Processing acidic solutions will accelerate wear of the horn.
• Using the horn at higher amplitude will cause faster wear.
• Smaller diameter horns wear faster than larger horns. Using a larger horn at a lower amplitude instead of a smaller horn at a higher amplitude will lead to longer useful life (but may have other effects on your process, so it may not be practical to optimize for the life of the horn).
• Laboratory scale models should have their converter cooled by clean, dry, compressed air if run for more than 15 minutes. The converter on pilot plant scale models should be cooled with compressed air at all times.
• Air used to cool a converter should be filtered by a 5 micron filter and pumped at 10 psi and at least 4 CFM.
• If your Sonicator is overloading frequently, you may need to replace your horn, you may be working with too viscous of a material, or the liquid you are processing may be outside the temperature range for your horn.

• Ultrasonic homogenizers must be used with liquids. It cannot be used for powders or other solids unless they are suspended in a liquid.
• Ultrasonic processing works best with materials which are low viscosity. Laboratory-scale units should be used with materials roughly 4000 centipoise or less (roughly the viscosity of thin honey or a thick maple syrup). If the liquid does not pour freely, it is too viscous to process. Pilot plant-scale units are even more sensitive to viscosity and should not be used with any material substantially more viscous than water.
• Gentle heating may be used to help reduce the viscosity of your material. horns can be used at temperatures up to 60°C.
• Sonicator horns are tuned for use with liquids between 0°C and 60°C. If you need to process a material which is outside this temperature range, contact us and we can provide a horn which is tuned to your temperature requirements.

• Due to larger horns operating at lower amplitudes, you may need to run for a longer period of time when switching to a larger horn when using the same instrument.
• If you need to process larger volumes than your Sonicator can accommodate in batch, consider using a flow cell setup.
• Keep in mind that larger diameter horns are less suitable for higher viscosities. If you are working with a higher-viscosity substance, you may not be able to scale up beyond the laboratory-scale systems.

• The compressor must always be air-cooled when using a continuous flow cell. Air used to cool a converter should be filtered by a 5 micron filter and pumped at 10 psi and at least 4 CFM.
• Substances must be well mixed before being pumped into the flow cell. It does not do you any good to pump your materials through in stages. If you are pumping from an external vessel, that vessel should have some form of mixing (for example an overhead or magnetic stirrer).
• Adjust the flow rate to ensure the sample has sufficient residence time inside the flow cell to achieve the desired result. If necessary, run the effluent stream back into your source vessel to be recirculated through the flow cell.
• Be aware of the flow rate and pressure limitations of the flow cell you are using and adhere to them.
• Any type of fluid pump can be used so long as it meets the flow rate and pressure requirements.
• Avoid pumping air through the flow cell. Turn the Sonicator off promptly when the process is complete. Ensure the setup is such that you are not pulling air into the line.