Finding the Best Ultrasonic Dispersion

One goal in method development is to disperse aggregates to the single particle state prior to measurement. Ultrasound is frequently used to disperse aggregated particles, but it is critical to determine the exact amount of energy required. In the past it was required to design an experiment to assess the effect of ultrasound on the state of dispersion. This is now automated with the Method Expert software features, exclusive to the LA-960 particle size analyzer. A case study of how the Method Expert was used during a structured method development process is explained below.

Download the White Paper about the revolutionary Method Expert software (You need to be logged in)

The LA-960 Method Expert: Guided, Automated Method Development Software
The LA-960 Method Expert: Guided, Automated Method Development Software

The sample used in the case study is a pigment that arrived in the lab as a powder to be dispersed in water. First, it was determined that no surfactant was required to wet the powder. Next, an initial experiment generated a bimodal result, indicating aggregation. The internal ultrasonic probe in the LA-960 was turned on for 10 seconds and the larger peak diminished, suggesting that ultrasound aids dispersion. Then the Method Expert function was opened and the screen below shows how the effect of ultrasound experiment was easily setup in three steps for automatic execution.

The Ultrasonic Optimization setup screen in the Method Expert
Click to enlarge: The Ultrasonic Optimization setup screen in the Method Expert

Using these settings the system automatically took 5 measurements with 30, 60, 90, 120, and 150 seconds of ultrasound at the highest power level of 7.  After all measurements are completed, the results are displayed in various formats so the user could select the optimum amount of energy (time).

Ultrasonic Treatment Wizard results from the Method Expert
Click to enlarge: Ultrasonic Treatment Wizard results from the Method Expert

The particle size distribution overlays and D10, 50, 90 vs. time plots can be viewed in greater detail, as seen below. Note that after 150 seconds a second larger peak (light blue) appears, indicating re-aggregation of the particles. This is also clearly seen by the sharp increase in D50 and 90 in the second plot.

The Method Expert provides Expert Advice information to guide the inexperienced user in selecting the best possible ultrasonic treatment.

Overlay of particle size distributions after varying ultrasonic treatments
Click to enlarge: Overlay of particle size distributions after varying ultrasonic treatments
Comparison of D10, D50, and D90 results after varying ultrasonic treatments
Click to enlarge: Comparison of D10, D50, and D90 results after varying ultrasonic treatments

It is always a good idea to document decisions made during method development. This is also automated with Method Expert, as seen below where the operator choose which results to save in various formats.

Saving, exporting, and printing Method Expert results
Click to enlarge: Saving, exporting, and printing Method Expert results

Stress Testing the Method

After the complete method is created, the next step is to test for repeatability. These calculations as defined in ISO 13320 are also automated calculations in the LA-960 software.

Automated coefficient of variation (CV%) calculation to evaluate method precision with the LA-960
Click to enlarge: Automated coefficient of variation (CV%) calculation to evaluate method precision with the LA-960

The user can then perform the other automated tests within the Method Expert software including structured tests to select the optimum:


LA-960 Product Page

LA-960

The LA-960 uses Mie Scattering (laser diffraction) to measure particle size of suspensions or dry powders. The speed and ease-of-use of this technique makes it the popular choice for most applications.