This work describes three different methods for detecting acidic groups copolymerized in poly(methyl methacrylate), poly(ethyl methacrylate), and poly(n-butyl methacrylate) chains using molecular spectroscopy. The first was based on the shift of the tautomeric equilibrium of 4-dimethylaminoazobenzene by acidic groups that modify the absorption band in the UV/vis spectra. We also show that the acidic groups present in the polymer influenced the anti-syn photoisomerization reaction of this dye. Further, a mercury-dithizonate complex was completely bleached when sorbed in poly(n-alkyl methacrylate) matrices containing acidic groups. Finally, Nile Blue A was used as a spectrophotometric probe to quantify the amount of acidic groups in these polymers. (C) 2004 Wiley Periodicals, Inc.