Sonicator FAQ

Sample Volume and Probe Size

Selecting the proper size probe is extremely important. Each probe has an approximate recommended sample volume range. See the chart below for guidance. For example the ½” probe can process approximately 20-250ml. Depending on the vessel size and shape, the ½” probe may have difficulty fitting inside a 20ml volume and a microtip may be a better option. Sample vessel size and shape is a factor when selecting a probe.

Small volumes require a small tip to fit inside the sample tube. Small tips (microtips) are recommended for processing samples inside small, thin vessels and never samples larger than 50ml. Microtips are high intensity and made for short processing times. A microtip will generate a considerable amount of heat in small volumes and therefore should be used in the pulse mode to prevent heat buildup.

Tip Depth / Foaming Issue

Probes/tips must be submerged properly. If the tip is not submerged enough the sample will foam or bubble. If the tip is too deep it will not circulate the sample effectively. Both conditions will end up with poor results. Foaming often occurs with samples volumes below 1ml. Foaming can also be caused when the amplitude setting is too high.

Power vs. Intensity

Power is the measure of the electrical energy that is being delivered to the converter. It is measured in watts and displayed on the sonicatorʼs screen. At the converter, the electrical energy is transformed into mechanical energy. It does this by exciting the piezoelectric crystals causing them to move in the longitudinal direction within the converter. This conversion from electrical into mechanical energy causes a motion that travels through the horn/probe causing the tip to move up and down.

The distance of one movement up and down is called its amplitude. The amplitude is adjustable. Each probe has a maximum amplitude value. For example, with a ½” diameter probe at setting 100%, the probe will achieve an amplitude of approximately 120μm. At setting 50% the amplitude is approximately 60μm. Note this value is approximate and not perfectly linear. Qsonica measures the amplitude of each probe at 100% and these values are published in the brochure.

Amplitude and intensity have a direct relationship. If you operate at a low amplitude setting, you will deliver low intensity sonication. If you operate at a high amplitude setting, you will have high intensity sonication. In order to be able to reproduce results, the amplitude setting, temperature, viscosity and volume of the sample are all parameters that need to remain consistent. The amplitude, not the power, is most critical when trying to reproduce sonication results.

Power has a variable relationship with amplitude/intensity. For example, sonicating water at setting 50% requires less wattage when compared to a viscous sample (such as honey). For both samples the amplitude/intensity is the same but the power/wattage will differ because the viscous sample will require more watts in order to drive the horn. The viscous sample puts a heavier load on the probe so they system must work harder to vibrate up and down at the same intensity.

Small fluctuations in the wattage display during sonication is normal. Major swings in wattage (+/-20 watts) may indicate a problem with the sample, setup or the sonicator itself.

Nanomaterials and Probe Size

Certain applications such as processing nanoparticles, often require long processing times. Using a larger probe will speed up processing and larger probes will not erode as quickly as smaller ones.

For example, using a Q700 with a ½” diameter probe will process a 50ml sample much faster than a Q125 or Q700 with a ¼” probe. In addition, smaller probes wear out faster and will need to be replaced more often. Over time using a larger system will end up costing less as you factor in the replacement cost of multiple probes.

Optimization

1. All applications require optimization of amplitude and time settings. Test your probe/tip with water using the same volume and sample vessel that you will use for actual sample processing. Observe how the liquid moves during sonication at different amplitude (intensity) settings. You should see and hear the cavitation and the entire sample volume should mix and flow well. 

2. Choose an amplitude setting that does not create foam or splashing as your starting point. Smaller volumes will require lower amplitude settings and shorter pulses of sonication. Larger volumes can be sonicated at 100% if necessary, to speed up processing times.

3. After choosing an amplitude setting, perform a time study by testing a sample at several time intervals and comparing results. Adjust amplitude and time as needed to obtain the desired result.

4. See the Resources section on the website for Protocols and Papers from other customers.

Booster Horn

A booster is a device that increases the amplitude (intensity) of a 1” or ¾” probe. For example, a 1 liter sample may be processed twice as fast with a 1” probe and 2:1 booster when compared to the 1” probe used alone. Smaller diameter probes already offer high intensity and will crack if used with a booster. The booster is recommended when processing difficult samples with volumes above 500ml.

How to Determine Energy Delivered

The WATTS reading displayed on the screen is the amount of electrical energy the ultrasonic generator delivers to the converter.

NOTE: The greater the resistance to the movement of the probe, the greater the amount of power that will be delivered to the probe. As a liquid is being processed, its viscosity and chemical characteristics will change causing the power readings to fluctuate.

How to calculate the power that is being delivered to a sample:

1. Turn on the equipment
2. Set the amplitude as required
3. With the probe in air, not immersed in a sample, record the amount of watts displayed on the power monitor
4. Without changing the amplitude setting, immerse the probe into the sample and record the amount of watts displayed on the power monitor
5. The difference in power readings between step 3 and 4, is the amount of power being delivered to the sample in watts
6. To obtain the power density in watts/cm², divide the number of watts obtained in step 5 by the area of the probe tip.

Area = (diameter/2)² x π or π r²

Area using a 3mm probe: 3mm/10 = .3cm = .15cm radius

.15²cm X 3.142 (π) = .0707cm²

Now divide the number of watts by the area of the probe.

Using 1 watt as an example, the power density would be 1/.0707 = 14 watt/cm²

NOTE: The intensity is expressed as watts per surface area. (watts/cm²)