pH, buffers, and buffer capacity are especially important in drug product formulation, since they affect the drug’s solubility, activity, absorption, and stability and the patient’s comfort.
A buffer is a system, usually an aqueous solution that can resist changes in pH upon addition of an acid or a base. Buffers are composed of a weak acid and its conjugate base or a weak base and its conjugate acid.
Buffers are prepared by one of these processes:
1. Mixing a weak acid and its conjugate base or a weak base and its conjugate acid
2. Mixing a weak acid and a strong base to form the conjugate base or a weak base and a strong acid to form the conjugate acid
Buffer capacity indicates the ability of a solution to resist changes in pH by either absorbing or desorbing H+ and OH- ions.
Henderson-Hasselbalch equation used to calculate pH –
pH =pKa + log (base/acid)
Note: Remember that the acid is the proton donor and the base is the proton acceptor.
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