Fig. 4: Optimization of the p-fluorophenol-FMN concentration ratio.

a Scheme representing the backside of the NMR chip and the two inlets (yellow and blue arrows) from the two pumps placed outside the NMR magnet and one outlet (green arrow) (Figs. 1, 2). The blue arrow represents the inlet were FMN was present. The total flow rate was 2 µL/min (represented by the constant size of the green arrow), varying it from 0 to 2 for each syringe (represented by the different lengths for the yellow and blue arrows). b Collection of ¹H NMR spectra for different p-fluorophenol—FMN ratio when changing flow rates for the two pumps; the integral values of both standards TFE and TFP were used to calculate the p-fluorophenol-FMN concentration ratio for d. c Photo-CIDNP ¹⁹F NMR spectra for the same conditions as in b. The purple rectangle indicates the spectra with a highest p-fluorophenol signal intensity. d Data points extracted from spectra shown in c for the integral value of p-fluorophenol as a function of the p-fluorophenol-FMN concentration ratio; The internal standard integral for TFE was taken as 100 units and the p-fluorophenol relative integral as a measure for photo-CIDNP efficiency.