A spot test for determination of residual TBA levels in 18F-radiotracers for human use using Dragendorff reagent

Abstract

When utilizing [¹⁸F]tetrabutylammonium fluoride ([¹⁸F]TBAF) in the synthesis of ¹⁸F-labeled radiotracers for clinical positron emission tomography (PET) imaging, it is necessary to confirm that residual TBA levels in formulated doses do not exceed established specifications (≤2.6 mg per patient dose). Historically this has been accomplished using HPLC, but this is time consuming for short-lived PET radiotracers and limited by the need for expensive equipment. This motivated us to introduce a TLC spot test for determining residual TBA, and we have developed a new method which employs the Dragendorff reagent. Herein we report details of the TLC method and use it to quantify residual TBA in different formulations of 6-[¹⁸F]fluoro-DOPA.

Fig. 1

TLC Staining of TBA standards using a) pre-developed iodoplatinate plates, b) manual Dragendorff stain, and c) iodine chamber

Fig. 2

Representative commercial Dragendorff stain of TBA standards

Fig. 3

Dragendorff stain of a) saline prepared TBA standards and b) PBS prepared TBA standards

Fig. 4

Analysis for other potential contaminants in radiotracer formulations using Diluted Dragendorff Stain (1:9)

Fig. 5

Representative Dragendorff testing of a 10 mL [¹⁸F]FDOPA dose