Development of a new TLC method for quality control of [11C]acetate

1916 Objectives: A popular published method for quality control of [11C]acetate is thin layer chromatography on NaOH-treated silica gel plates. However, in our hands this method gave inconsistent results. Thus the objective of this study was to develop a more reliable TLC method for QC of [11C]acetate Methods: Four TLC systems were studied: (1) silica gel plates dipped in saturated NaOH/MeOH and air dried, eluted with MeOH; (2) untreated SiO2, MeOH eluent; (3) SiO2, acetone/H2O/CHCl3/EtOH/NH4OH (60/2/6/10/22); and (4) SiO2, acetone/EtOH/NH4OH (65/10/25). [11C]Acetate was synthesized by reaction of cyclotron generated [11C]CO2 with 100 umol MeMgCl in THF and purified by sequential cation exchange, halide exchange and anion exchange cartridges. [11C]Carbonate was made by bubbling [11C]CO2 into dilute NaOH. Radioactive sample chromatograms were quantitated on a Bioscan AR-2000 TLC scanner. Carrier acetic acid and sodium acetate were applied to separate plates and visualized with methyl red-bromophenol blue spray + heat. Results: The NaOH-treated plates gave variable results (Rf 0.58-0.84) in different experiments. Storing the plates in a desiccator or oven drying did not improve their performance. In contrast, the three other systems gave reproducible results both with carrier acetic acid and with [11C]acetate. System 2 (the only one without base) also resolved ionic acetate from acetic acid. [11C]Carbonate did not migrate (Rf 0.0) on any system. Conclusions: System 4, silica gel eluted with acetone/ethanol/ammonium hydroxide, was the simplest system giving reproducible results in an ideal Rf range (Rf 0.5) and was selected for routine QC. Research Support (if any): Supported by NIH/NCI # R25T-CA092043 and Vanderbilt Department of Radiology.