Floating dosage forms rarely dissolve at a reproducible rate. Using a sinker in Apparatus 2 fixes the dosage form to a certain point and aids reproducibility. Sinkers can also be useful where dosage forms may stick to the sides of the vessel.
General guidelines to consider when choosing a sinker for your application include:
- Sinker Size - the sinker should have minimal surface contact with the tablet as this can affect the dissolution rate.
- Sinker Weight - should be kept to a minimum - just enough to have a desired effect.
- PTFE Coated Sinkers Magnetic - used with magnetic retrieval systems, or where there may be a reaction between steel and the tablet.
- Uncoated - type 316 stainless steel sinkers are more durable than coated sinkers.
- Basket Sinkers - can be used but care should be taken that the outer coating of the tablet does not clog the mesh
- Wire Spirals - should be as wide as practically possible to avoid clogging