What is the most efficient way to make up a hepes buffer at ph 8.5?

value of HEPES is 7.5.

A proper amount of HEPES is mixed with distilled water (sterilized) to avoid any contamination. After that, check the pH with the help of pH scale or pH meter.

First, take the basic form of HEPES and then add hydrochloric acid drop by drop to bring down the pH at 8.5.

When pH reaches 8.5; the buffer solution is filtered and placed in the  glass container and then covered by aluminium foil.