Table 3. Rationales Behind the Choice of Tetraalkylated Eluting Anions and Physiochemical Properties of the Different Solvent Used for the Multiparametric Screen of Elution Conditions.

tetraalkylammonium salts	rationale
Bu4NOTf	The lower pKa of OTf– compared to that of the OMs– of Bu4NOMs should displace lower amounts of preconditioning anions during the elution process, resulting in a less basic eluate and therefore enabling labeling of tracers under milder reaction conditions.
Bu4NH2PO4	Due to the buffering capabilities of Bu4NH2PO4, we decided to test this compound. This salt should neutralize more basic preconditioning anions.
Et4NHCO3	This salt is commonly used for elution in nucleophilic 18F-radiolabeling and is used as a comparison.37,38

solvent		proton affinity	H-bonding properties
DMSO	aprotic	protophilic	no HBD and HBA exist
MeCN	aprotic	protophobic	no HBD and very weak HBA
tBuOHa	protic	amphiprotic	both HBD and HBA properties

^aMixed with ∼17% v/v MeCN added to make it liquid at room temperature.