An internal standard suitable for quantitation of 1-(3-Chlorophenyl)piperazine levels in urine or blood by GC/MS or LC-MS/MS. 1-(3-Chlorophenyl)piperazine, also known as mCPP, is a phenyl piperazine derivative and club/designer drug used in combination with Benzylpiperazine (BZP) and Trifluoromethylphenylpiperazine (TFMPP) as an alternative to LSD and MDMA. mCPP is also the primary, active metabolite in urine of the antidepressants trazodone and nefazodone.