RPRD | Direct measurement of residual Kryptofix 222TM in the final [18F]FDG p…

Yong-Seok Lee, Yong-Hyun Cho, Jae-Hyung Lee, Yun-Sang Lee, Hong-Jae Lee, Hyun-Ju Kim, Dong Soo Lee , Jae Min Jeong*

PET center, Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea

Purpose

Residual Kryptofix 222TM  (K222) in [18F]FDG product should be checked and kept lower than 50 ug/mL according to the US-FDA guidance. The visual method using Color Spot Test (CST) Kit is widely used for the routine quality control (QC) for residual K222. However, the test results are dependent to the subjective decision of operators. Thus, we measured the reference standard solution of K222 with the concentration range of 2~200 ug/mL using a liquid chromatography and mass spectrometer (LC-MS) system and compared with the CST result.

Materials and Methods

We have quantified the standard reference solution of K222 with the concentrations of 2, 5, 10, 20, 40, 50, 60, 100, and 200 ug/mL using CST kit color change and LC-MS measurement of exact quantity. And then, the K222 concentration in routine [18F]FDG samples also were directly measured by LC-MS.

Results

Total QC procedure took 8 min for CTS kit and 4 min for LC-MS system. Pale purple color was observed at 2~ 20 ug/mL and dark purple color and a boundary line was clearly shown at 40~ 60 ug/mL of K222 solution by CTS kit method. At 100 and 200 ug/mL, the color of CTS kit turned to purple gray and a boundary line disappeared. Calculated  concentrations  of  standard K222  solution  determined  by  LC-MS  were 2.12±1.19, 5.68±0.17,  9.65±0.11,  23.34±4.46,  40.32±1.29,  49.75±0.93, 60.16±2.99, 109.71±8.32, and 176.91±8.18 ug/mL (n=3), respectively. And residual K222 concentration of routine [18F]FDG sample was 1.04 ± 0.29 ug/mL (n=46) by the LC-MS system.  On the other hand,  it  could  not  be measured  by CTS  kit because of low sensitivity of the method.

Conclusion

We compared the CTS kit and LC-MS method for routine QC of residual K222 concentration from [18F]FDG sample, and found LC-MS method showed more quantitative and linear result than CTS kit method in all range of the standard reference solution of K222.