Description General description This stable-labeled internal standard is suitable for quantitation of 4-chloroisobutyryl fentanyl levels in urine, serum, or plasma by LC/MS or GC/MS for clinical toxicology, forensic analysis, or isotope dilution methods. 4-Chloroisobutyryl fentanyl is an opioid analgesic analog of fentanyl and has been sold as a designer drug on the illicit drug market. Legal Information CERILLIANT is a registered trademark of Cerilliant Corporation