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

Figure 5

The selectivity of PAD in different papers: (1) Whatman No. 1, (2) Whatman No. 4, (3) Whatman No. 6, (4) Whatman 1 Chr. The PAD gives a different color on (a) reagent, (b) allopurinol, (c) paracetamol, and (d) caffeine.

(a)

(b)

(c)

(d)