residues from all possible surfaces Take pH reading with pH meter and record as glassware pH Any significant increase in pH indicates possible alkaline detergent residue. A... to measuring the pH with a meter. Note regarding pH paper: detergents and surface active agents can interfere with some pH paper by causing a decrease of several pH units in reading... residue. B. pH Indicator Method for Alkaline Detergents Materials 0.04% Bromothymol Blue (Aldrich 31,875-2), or prepare in 250 ml reagent grade water with 16 ml of 0.01 N NaOH to 0.1 g...