A method comprising: (a) reacting in acetonitrile a precursor compound of Formula I: BTM-LINKER-LG (I) wherein: BTM is a biological targeting moiety; LINKER is an alkylene or an alkoxyalkylene; and, LG is a sulfonate-containing leaving group; with 18 F-fluoride to obtain a crude reaction mixture comprising an 18 F-labelled compound of Formula II: BTM-LINKER- 18 F (II) wherein BTM and LINKER are as defined for Formula I; (b) diluting the crude reaction mixture obtained in step (a) to obtain a diluted crude reaction mixture; (c) purifying the diluted crude reaction mixture obtained in step (b) by means of one or more solid phase extraction (SPE) cartridges to obtain a purified compound of Formula II where said purifying comprises the sequential steps of: (i) transferring said diluted crude reaction mixture to an SPE cartridge; (ii) optionally passing water through said SPE cartridge; (iii) passing a wash solution comprising an organic solvent through said SPE cartridge; (iv) optionally passing water through said SPE cartridge to remove said organic solvent; and, (v) passing an elution solution comprising ethanol through said SPE cartridge to elute said compound of Formula I from said SPE cartridge; wherein step (b) includes adding a hydrolysing reagent to said crude reaction mixture and/or said water of step (ii) and/or step (iv) comprises a hydrolysing reagent; and wherein said precursor compound is a compound of Formula Ia: and said 18 F-labelled compound is a compound of Formula IIa: wherein: R' is an optionally substituted C 1-6 alkyl; R 2 is hydrogen or halo; and W is an optionally substituted alkylene or heteroalkylene. (a) reacting in acetonitrile a precursor compound of Formula I: BTM-LINKER-LG (I) wherein: BTM is a biological targeting moiety; LINKER is an alkylene or an alkoxyalkylene; and, LG is a sulfonate-containing leaving group; with 18 F-fluoride to obtain a crude reaction mixture comprising an 18 F-labelled compound of Formula II: BTM-LINKER- 18 F (II) wherein BTM and LINKER are as defined for Formula I; BTM is a biological targeting moiety; LINKER is an alkylene or an alkoxyalkylene; and, LG is a sulfonate-containing leaving group; (b) diluting the crude reaction mixture obtained in step (a) to obtain a diluted crude reaction mixture; (c) purifying the diluted crude reaction mixture obtained in step (b) by means of one or more solid phase extraction (SPE) cartridges to obtain a purified compound of Formula II where said purifying comprises the sequential steps of: (i) transferring said diluted crude reaction mixture to an SPE cartridge; (ii) optionally passing water through said SPE cartridge; (iii) passing a wash solution comprising an organic solvent through said SPE cartridge; (iv) optionally passing water through said SPE cartridge to remove said organic solvent; and, (v) passing an elution solution comprising ethanol through said SPE cartridge to elute said compound of Formula I from said SPE cartridge; (i) transferring said diluted crude reaction mixture to an SPE cartridge; (ii) optionally passing water through said SPE cartridge; (iii) passing a wash solution comprising an organic solvent through said SPE cartridge; (iv) optionally passing water through said SPE cartridge to remove said organic solvent; and, (v) passing an elution solution comprising ethanol through said SPE cartridge to elute said compound of Formula I from said SPE cartridge; wherein said precursor compound is a compound of Formula Ia: and said 18 F-labelled compound is a compound of Formula IIa: wherein: R' is an optionally substituted C 1-6 alkyl; R 2 is hydrogen or halo; and W is an optionally substituted alkylene or heteroalkylene. R' is an optionally substituted C 1-6 alkyl; R 2 is hydrogen or halo; and W is an optionally substituted alkylene or heteroalkylene. <EOS>