4-hydroxy-3-methoxyphenylglycol ( hmpg ) with the three hydrogen atoms in the side-chain replaced with deuterium ( hmpg-d3 ) was used as the internal standard in the mass fragmentographic determination of free and conjugated hmpg in human urine , cerebrospinal fluid and plasma and in rat urine , liver and brain .
C0020275
hydrogen
C0011744
deuterium