Comparison of purification methods for [13N]NH3 production

Introduction:

There are two methods for the production of N-13 ammonia. The Gas Phase process utilizes a disposable cassette after the ¹⁶O(p,α)¹³N nuclear reaction, while the In-target process directly generates it through the nuclear reaction using ethanol in water. Although In-target process has the advantage due to its simplicity and cost-effectiveness, it is accompanied by the disadvantage of impurities. Therefore, we have performed a comprehensive comparison of multiple purification methods to eliminate these impurities.

Methods: We used a PETtrace 800 cyclotron and PT800 ¹³NH₃ target system (GE Healthcare, IL, U.S.A). In the In-target process, 5 mM ethanol (SAMCHUN Co., KOREA) in D.W. (DAIHAN Co., KOREA) served as the target material and [¹³N]NH₃ was directly produced through ¹⁶O(p,α)¹³N nuclear reaction with hydrogen. Due to the generation of impurities such as ¹³NO₂^-, ¹³NO₃^-and ¹⁸F^-, it is recommended to employ purification using a strong anion exchange cartridge such as SAX (Agilent Technologies, CA, U.S.A) and QMA (Agilent Technologies, CA, U.S.A). When the [¹³N]NH₃ was analyzed after purification using Multi channel analyzer (CANBERRA PACKARD, Austria), the long-lived nuclides such as ⁴⁰K, ⁵⁶Mn, ⁵⁷Co and ⁹⁷Zr were detected. To eliminate these long-lived nuclides, [¹³N]NH₃ directly produced in a cyclotron was passed through a strong anion exchange cartridge and then collected in a CM cartridge (Waters Corporation, MA, U.S.A). The collected [¹³N]NH₃ was eluted with saline solution(BD, NJ, U.S.A) resulting in no detectable impurities by the measurement using Multi channel analyzer.

Results: In the purification method using only an anion exchange cartridge, many long-lived nuclides such as ⁴⁰K, ⁵⁶Mn, ⁵⁷Co and ⁹⁷Zr were detected. However, in the purification method using both a strong anion exchange cartridge and a CM cartridge, neither long-lived nuclides nor impurities were measured.

Conclusions: We successfully synthesized [¹³N]NH₃ using the In-target process and confirmed that impurities can be effectively eliminated by using a standard anion exchange cartridge in conjunction with a CM cartridge.