Fig. 3

Figure showing SalACP-mediated quantification of aqueous HCHO. (A) Scheme showing the reaction of SalACP with HCHO. Following initial imine formation, a 2-aza-Cope rearrangement occurs to form an imine intermediate. Subsequent hydrolysis gives a primary amine and salicylaldehyde, which can be detected using GC–MS. All steps in the reaction are reversible, while it is probable that the rearrangement is accelerated by protonation on the nitrogen. (B) ¹H NMR spectra showing time-dependent formation of salicylaldehyde from the reaction of SalACP (200 µM) and HCHO (100 µM) in buffered water. ¹H resonances corresponding to the amine product are also apparent. (C) Graph showing quantification of salicylaldehyde in 100 mM sodium phosphate buffer pH 7.4 using head-space SPME–GC–MS. A linear response is observed down to 1 nM (R² = 0.999). (D) Graph showing quantification of salicylaldehyde derived from the reaction of SalACP and HCHO in 100 mM sodium phosphate buffer pH 7.4 using head-space SPME–GC–MS. A linear response is observed between 1 µM and 75 µM (R² = 0.961). (E) Graph showing quantification of salicylaldehyde derived from the reaction of SalACP and HCHO in 100 mM sodium phosphate buffer pH 7.4 using immersive SPME–GC–MS. A linear response is observed between 10 µM and 100 µM (R² = 0.985). Saturation is observed above 100 µM.