*3.5. Stability in Seawater*

For the stability assay, 200 μL of stock solution was added to a total of 4 glass vials and each vial was diluted with snSW in order to obtain a final concentration of 200 μM in each vial. After that, 3 of the 4 vials were wrapped in aluminum and stored under di fferent conditions for a period of several months: 1 vial was stored in the refrigerator at a temperature of 4 ◦C; 1 vial was stored at 18 ◦C; 1 vial was stored at 24 ± 1; and the other vial was exposed to natural light at 24 ± 1. These procedures were made in duplicate. The same assay was also performed using UPW for comparative purposes. Periodically, an aliquot of each vial was directly injected into the IP-RP-HPLC system without any extraction procedure, and the peak area of GAP was interpolated into the calibration curve.
