Why Did I Get a Negative Reading for “O” Alkalinity?

Occasionally, I will see people posting questions in forums about their “O” alkalinity test result being a negative number. Someone stated that their pH was up at 11, so they knew there had to be “OH” alkalinity in the water! How can that be? The simple answer: They are using the “2P-M” method for calculating “O” alkalinity.

More and more boiler water treatment programs are using polymer for deposit control. What many people do not realize is that the polymer will titrate as “M” or “Total” alkalinity. When there is a high amount of polymer in the boiler water, the “M” number gets large enough to reduce the “2P-M” value to zero and sometimes even to a negative number. The way to combat this problem is to perform a direct titration using the barium chloride method. Addition of barium chloride to the boiler water sample removes the carbonate and bicarbonate alkalinity species, leaving only the hydroxide, or “O” alkalinity, to be titrated to the colorless endpoint. No additional math is needed. Now life is good, and you are also now that you are getting results that make sense. Another bonus … you will probably need less alkalinity additive to meet your program guidelines!