What chemical would you use to confirm the presence of vitamin C?

To confirm the presence of vitamin C (ascorbic acid), you can use a solution of iodine. When iodine is added to a sample containing vitamin C, it will react and become decolorized, indicating the presence of vitamin C. This reaction occurs because vitamin C reduces iodine, turning it from a brownish color to clear. A titration method can also be utilized for quantitative analysis.