- Separation Methods are vital in pharmaceuticals, chemistry, food, and environmental analysis.
- Separation Methods involve techniques to isolate and purify components from mixtures efficiently.
- These are based on the physical separation of particles by size, using external forces.
Sieving
- Applicable to coarse particles (>50 µm).
- A stack of sieves with decreasing mesh size is used.
- The sample is placed on the top sieve and shaken (manually or mechanically).
- The mass retained on each sieve gives a weight-based size distribution.
Advantages:
- Simple and inexpensive.
- Common in quality control for bulk powders.
Limitations:
- Not suitable for particles <50 µm.
- Irregular particles may pass or be retained inconsistently.
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Sedimentation (Stokes’ Law-Based)
- Particles settle in a fluid; settling velocity depends on size, shape, and density.
- Based on Stokes’ Law:
- $v = \frac{2 r^{2} (\rho_{p} – \rho_{f}) g}{9 \eta}$
- Where:
- v = settling velocity
- r = particle radius
- = densities of particle and fluid
- = fluid viscosity
Methods:
- Andreasen pipette (manual sampling at different depths and times).
- Photosedimentation (automated; based on light blockage).
Advantages:
- Suitable for 1–100 µm.
- Gives volume-based distribution.
Limitations:
- Assumes spherical particles.
- Affected by temperature, agitation, and fluid viscosity.
