The powdered drug is separated according to its particle size using several sieves in a nest. These are subjected to different types of agitation, so that size separation is rapid.
Construction of Sieve Shaker Machine:
- Standard sieves of different mesh numbers are available commercially as per the specifications of IP and USP. These sieves are fixed in a mechanical shaker apparatus (Figure).
Working of Sieve Shaker Machine:
- Sieves are arranged in a nest with the coarsest at the top. A sample (50 g) of the powder is placed on the top sieve (Figure). This sieve set is fixed to the mechanical shaker apparatus and shaken for a certain time (20 minutes). The powder retained on each sieve is weighed.
- Care should be taken to get reproducible results. The type of motion influences sieving; vibratory motion is most efficient, followed by side-tap motion, bottom-pat motion, rotary motion with the tap, and finally rotary motion. The type of motion and intensity of the shaker are fixed and standardized. Shakers are commercially available.
- Other factors are the weight of the sample and the duration of shaking. Sieves produced by photo-etching and electro-forming techniques are used to get a better estimate of the size distribution analysis with a lower limit of estimation of particle diameter 50 µm.
- It is inexpensive, simple, and rapid with reproducible results.
- The lower limit of particle size is 50 µm.
- If the powder is not dry, apertures get clogged with particles, leading to improper sieving.
- During shaking, attrition (particles colliding with each other) occurs causing size reduction of particles. This leads to errors in estimation.
Variants of Sieve Shaker Machine:
- Electromagnetic sieve shaker-It is useful for analyzing powders under controlled conditions. Sonic sifter This apparatus utilizes sonic oscillations. Mechanical pulse action is used to reduce blinding and agglomeration in the sub-sieve sizes.
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