The pH-dependent oxidation, affecting the rates and type of products, has drawn attention to the role of ionization and protonation of the zwitterion folate/folic acid as a mechanism.(15, 38) Akhtar and co-workers studied the effect of pH in the pH range 2–10 on photodecomposition of folic acid.(46, 47) According to their results folic acid exhibited best stability at highly alkaline pH 10.0, whereas its stability was lowest and susceptibility to photolysis was highest in the acidic range (pH 2–4). This clearly showed that photolysis of folic acid is a pH-dependent reaction and occurs more rapidly at low pH when folic acid exists predominantly as a neutral species. More recently, Martin et al. proposed a mechanism of photolysis of folic acid where UV radiation at 350–400 nm caused formation of pterin radicals, which were then oxidized to the known photoproduct 6-carboxypterin