1-Methyl-4-nitrosopiperazine-d11 (MNP-d11) is the deuterium labeled 1-Methyl-4-nitrosopiperazine (HY-W663740). 1-Methyl-4-nitrosopiperazine (MNP, MeNP,N-Methyl-N-nitrosopiperazine) is a potential impurity in sartans, non-steroidal anti-inflammatory drugs (NSAIDs), and thiazide diuretics[1].