A system for measuring and controlling the concentration of a chemical agent in a solution has a reaction cell for receiving a sample, a titrant dropper for releasing one or more drops of titrant into the sample, a first photosensor for sensing disruptions of light for every drop of titrant released, and a controller that communicates with the photosensor and computes the concentration of the chemical agent based on the number of disruptions of light at the photosensor. The present invention also includes a method for sensing and controlling the concentration of a chemical agent in a solution. The method includes having a sample containing the chemical agent, triggering the release of a number of drops of titrant into the sample, detecting the number of drops released into the sample, and computing the concentration of the chemical agent in the sample based on the number of drops of titrant released into the sample.