I'm not sure if this will help you as your H2O2/PAA concentration is on ppm level in a disinfectant (I think PAA is bactericidal at 10 ppm and fungicidal at 30 ppm), but we determine H2O2/PAA as a 2-point titration in other applications where PAA concentrations range from 1 % to approx. 40 %.
Unfortunately, I cannot share our exact method here, but you can find a similar method below:
If the sample is too dilute for titration we use an ABTS based colorimetric method to determine PAA and the TiO-oxalate based colorimetric method for H2O2 quantification.
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