SNaP-C: Validation of a novel, selective silver nanoparticle antioxidant capacity assay for Vitamin C content in beverages

A validated silver nanoparticle assay (SNaP-C) for quantitation of Vitamin C, as ascorbic acid (AA) and total AA (TAA), was applied to 31 beverages. SNaP-C assay results (LOD of 2.2 mg/L AA) were compared to AA and TAA determined by high-performance liquid chromatography with UV/Vis (LOD = 0.4 mg/L AA), and two well-known assays. All approaches were calibrated using meta-phosphoric acid stabilized AA, where the reducing agent tris(2-carboxyethyl) phosphine hydrochloride was added to convert dehydroascorbic acid to AA for determination of TAA. Statistical comparisons of these four resulting datasets were completed. SNaP-C and HPLC were not statistically significantly different (P > 0.05) for comparison of AA and TAA (mg/L) in these samples, whereas the CUPRAC and Folin-Ciocalteu assays statistically significantly overestimated values of AA and TAA content, respectively. The SNaP-C method is a novel assay that has high specificity for AA capable of quantifying TAA with addition of TCEP.