Top 10 Wet Method Development Tips

  1. Design every method for maximum precision: repeatability and reproducibility.
  2. Study different sampling techniques to help minimize error. This is particularly important for materials with small outlier populations. 
  3. Choose a solvent which has negligible reactivity with the material, wets the material without requiring copious surfactant, has a viscosity which can be pumped in the analyzer, and has a refractive index different than the material. 
  4. If surfactant is required to help wet a powder, use as little as possible to minimize bubbling. If bubbles form, use low power internal ultrasonics to remove them during measurement.
  5. Too much material has been added to the analyzer when a new sub-100 nm population appears in the particle size distribution. This is caused by multiple scattering and can be avoided by adding less material (higher %Transmittance).  
  6. Choose a refractive index by studying references (i.e. CRC Handbook), applying known information about the material, or, if no information is available, by minimizing the R-parameter.  
  7. Refractive index (RI) affects the accuracy of the particle size distribution, but has a much smaller effect on the analyzer's ability to detect changes to that distribution. In practice, even an incorrect RI can be used to successfully monitor the quality of a material or process.
  8. Study the effect of ultrasound on the material. The real-time PSD display indicates when the material has been fully dispersed by ultrasound.
  9. Evaluate the method's robustness by calculating the coefficient of variation for the D10, D50, and D90 values across a minimum of three measurement results. The LA-960 automatically makes these calculations.  
  10. Use the LA-960 Method Expert to automate and guide this important process.

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