Alteration of chemical behavior of L-ascorbic acid in combination with nickel sulfate at different pH solutions in vitro

Objective

To evaluate the alteration of chemical behavior of L-ascorbic acid (vitamin C) with metal ion (nickel) at different pH solutions in vitro.

Methods

Spectra of pure aqueous solution of L-ascorbic acid (E mark) compound and NiSO₄ (H₂O) (sigma USA) were evaluated by UV visible spectrophotometer. Spectral analysis of L-ascorbic acid and nickel at various pH (2.0, 7.0, 7.4 and 8.6) at room temperature of 29 °C was recorded. In this special analysis, combined solution of L-ascorbic acid and nickel sulfate at different pH was also recorded.

Results

The result revealed that λ_max (peak wavelength of spectra) of L-ascorbic acid at pH 2.0 was 289.0 nm whereas at neutral pH 7.0, λ_max was 295.4 nm. In alkaline pH 8.6, λ_max was 295.4 nm and at pH 7.4 the λ_max of L-ascorbic acid remained the same as 295.4 nm. Nickel solution at acidic pH 2.0 was 394.5 nm, whereas at neutral pH 7.0 and pH 7.4 were the same as 394.5 nm. But at alkaline pH 8.6, λ_max value of nickel sulfate became 392.0 nm. The combined solution of L-ascorbic acid and nickel sulfate (6 mg/mL each) at pH 2.0 showed 292.5 nm and 392.5 nm, respectively whereas at pH 7.0, L-ascorbic acid showed 296.5 nm and nickel sulfate showed 391.5 nm. At pH 7.4, L-ascorbic acid showed 297.0 nm and nickel sulfate showed 394.0 nm in the combined solution whereas at pH 8.6 (alkaline) L-ascorbic acid and nickel sulfate were showing 297.0 and 393.5 nm, respectively.

Conclusions

Results clearly indicate an altered chemical behavior of L-ascorbic acid either alone or in combination with nickel sulfate in vitro at different pH. Perhaps oxidation of L-ascorbic acid to L-dehydro ascorbic acid via the free radical (HSc*) generation from the reaction of H₂ASc + Ni (II) is the cause of such alteration of λ_max value of L-ascorbic acid in the presence of metal nickel.