Novel Spectrophotometric Method for the Quantitation of Urinary Xanthurenic Acid and Its Application in Identifying Individuals with Hyperhomocysteinemia Associated with Vitamin B₆ Deficiency

Figure 2

Reduction of Fe³⁺-TPTZ complex by XA is a time-dependent process. The increment of absorption at 593 nm reaches a plateau at approximately 30 min. For accuracy, the reaction time for the proposed method should be set at 30 min. (●−−●) = 4 μg XA in MeOH and (○--○) = 8 μg XA in MeOH.