Which of the following buffers is used in the IFCC recommended method for ALP?

The correct choice is 2-Amino-2-methyl-1-propanol, commonly known as AMP, which is specifically recommended in the IFCC method for measuring alkaline phosphatase (ALP) activity. This buffer maintains a stable pH necessary for the enzyme activity during the assay process.

AMP is effective in this context because it provides a suitable environment that optimizes the enzyme's reaction conditions, ensuring accurate measurement of ALP levels in serum or plasma samples. Other buffers may not maintain the required pH range or could interact differently with the enzyme, affecting the assay's sensitivity and specificity.

Each of the other options—glycine, phosphate, and citrate—may be used in different biochemical assays, but they do not provide the same optimal conditions required for the IFCC recommendation for ALP measurement. For example, phosphate buffers are often used in various enzymatic assays, but they can be less effective in stabilizing the pH in the same way as AMP does under the specific conditions of the ALP assay.