Abstract: In a printed circuit board manufacturing process, a resist stripping solution blending organic amines with water is used for stripping the photoresist completely from the board. An apparatus for controlling this resist stripping solution comprises a toroidal conductivity controller for measuring the solution conductivity, which correlates to solution concentration. This same apparatus is equipped with a resist stripping solution discharge device for discharging the resist stripping solution and water replenishing device for replenishing water by detecting the liquid level of the resist stripping solution by a liquid level gauge. As the water is replenished, the solution conductivity is lowered; thereby activating the toroidal conductivity controller to add concentrated resist stripping chemistry proportionally to the deviation from the conductivity controller set point. This same apparatus is equipped with a measuring device for measuring the total consumed organic amine reactants.