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Pak Chu PhD.

Division of Residue Chemistry


Dr. Pak Chu is a research chemist with the Division of Residue Chemistry in the Office of Research at FDA’s Center for Veterinary Medicine (CVM). He received his BS, MS, and PhD degrees from the University of California, Davis. He joined FDA in 1992. His primary responsibilities include development of analytical methods for regulatory use, coordination of method trials, and investigation of metabolism and disposition of drugs in animals.


  • Analytical methods development for drug residues in biological matrices.
  • Metabolism and disposition of drugs in animals using radiotracer techniques.
  • Investigation of new approaches to detect and quantify intact phase II metabolites using liquid chromatography–tandem mass spectrometry.

Select Publications

Chu, Pak-Sin, Eric Evans, and Sara Sklenka. 2016. “Liquid Chromatography-Tandem Mass Spectrometry for the Determination of Nortestosterone Glucuronide in Rainbow Trout Muscle,” Proceedings of EuroResidue VIII: 390–94.

Nishshanka, Upul, Hiranthi Jayasuriya, Chaitali Chattopadhaya, Philip J. Kijak, Pak-Sin Chu, Renate Reimschuessel, Andriy Tkachenko, Olgica Ceric, and Hemakanthi G. De Alwis. 2016. “Screening for toxic phorbol esters in jerky pet treat products using LC–MS,” Journal of Chromatography B, 1020: 90–95.

Nishshanka, Upul, Pak-Sin Chu, Eric Evans, Renate Reimschuessel, Nicholas Hasbrouck, Kande Amarasinghe, and Hiranthi Jayasuriya. 2015. “Tentative Structural Assignment of a Glucuronide Metabolite of Methyltestosterone in Tilapia Bile by Liquid Chromatography–Quadrupole-Time-of-Flight Mass Spectrometry,” Journal of Agricultural and Food Chemistry, 63: 5753–60.

Amarasinghe, Kande, Pak-Sin Chu, Eric Evans, Renate Reimschuessel, Nicholas Hasbrouck, and Hiranthi Jayasuriya. 2012. “Development of a Fast Screening and Confirmatory Method by Liquid Chromatography–Quadrupole-Time-of-Flight Mass Spectrometry for Glucuronide-Conjugated Methyltestosterone Metabolite in Tilapia,” Journal of Agricultural and Food Chemistry, 60: 5084–88.

Contact Information
Pak Chu
+1 (240) 402-5498
+1 (301) 210-4685
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