Guanidine Thiocyanate (CAS # 593-84-0). You state that the subject product, Guanidine Thiocyanate (CAS # 593-84-0), which is also called Guanidinium Isothiocyanate is a pure chemical compound. It is used as a general protein denaturant, although it is most commonly used as a nucleic acid protector in the extraction of DNA and RNA from cells. The Guanidine Thiocyanate that you wish to import into the United States is indicated to be “99+% pure”, and is used as a reagent in the preparation of test kits.
[1] Please importantly note that only the relevant portion of the related is displayed above. You may refer to the said customs ruling for the entire ruling explanation.
[1]. https://rulings.cbp.gov/ruling/N315425