A buffer is composed of a weak acid and the corresponding conjugate base, so what is the meaning of a phosphate-citric acid buffer (McIlvaine buffer). In what situations is it used?
You could really use this buffer for any sort of a biological application that you might use Tris, HEPES, phosphate, etc. for. This particular buffer is unique in that it can provide buffering capacity across a very broad pH range (~2-8) because both the acid (citric acid) and the base (dibasic phosphate) are polyprotic, meaning they can donate/accept multiple protons. As a result, the pH response curve of this buffer crosses multiple pKa values which are relatively closely spaced within that pH region.
You could really use this buffer for any sort of a biological application that you might use Tris, HEPES, phosphate, etc. for. This particular buffer is unique in that it can provide buffering capacity across a very broad pH range (~2-8) because both the acid (citric acid) and the base (dibasic phosphate) are polyprotic, meaning they can donate/accept multiple protons. As a result, the pH response curve of this buffer crosses multiple pKa values which are relatively closely spaced within that pH region.
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