Design and Optimization of Colorimetric Paper-Based Analytical Device for Rapid Detection of Allopurinol in Herbal Medicine

Figure 3

Color change of Whatman filter paper in the presence of allopurinol in a variation of immersion time: (1) 10 min; (2) 20 min; (3) 40 min; (4) 60 min. (a) Folin-Ciocalteu reagent + allopurinol; (b) p-DAB reagent + allopurinol; (c) Tollens reagent + allopurinol.

(a)

(b)

(c)