the concentration of the NaOH was
sufficient to change the color of the phenolphthalein once it
had penetrated the detection reservoir. The situation was
similar when using the μPAD for 0.01 to 0.1 M NaOH; namely,
the concentrations of NaOH were higher than 0.01 M when the
concentrations of the acid were lower than that of NaOH