TOC Theory

Source: Teledyne Tekmar

TOC is a popular analytical technique in water quality testing, as seen in many official analytical methods today. The United States Pharmacopoeia (USP), European Pharmacopoeia (EP) and Japanese Pharmacopoeia (JP), recognizes TOC as a required test for purified water and water for injection (WFI). As stated in USP method <643> on Total Organic Carbon:

"TOC is an indirect measure of organic molecules present in pharmaceutical waters measured as carbon. Organic molecules are introduced into the water from the source water, from purification and distribution system materials, and from biofilm growing in the system. TOC can also be used as a process control attribute to monitor the performance of unit operations comprising the purification and distribution system."

TOC has also found wide acceptance in the biotechnology industry to assist in the validation cleaning procedures, especially clean-in-place (CIP). TOC concentration levels can be used to track the success of these cleaning procedures.

Since the relationship between Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and TOC was established in the 1970s, TOC analyzers have become an analytical backbone in many water treatment and quality control laboratories worldwide. In environmental applications, TOC is an essential environmental parameter used to measure wastewater from municipal and industrial sources.

TOC has a long history as being a world-renowned analytical technique to measure water quality during the drinking water purification process. Before source water is treated for disinfection, TOC provides an important role in quantifying the amount of natural organic matter (NOM) in the water source. Many researchers have determined that higher levels of NOM in source water during the disinfection process will increase the amount of carcinogens, called disinfection by-products (DBPs), in the processed drinking water. Today, Environmental Protection Agencies regulate the trace limits of DBPs in drinking water. In recent methods, such as USEPA method 415.3, D/DBP rule, the amount of NOM is regulated to prevent the formation of DBPs in finished waters.

TOC Overview

TOC analyzers can measure:

  • Total carbon (TC)
  • Total organic carbon (TOC)
  • Inorganic carbon (IC)
  • Purgeable organic carbon (POC)
  • Nonpurgeable organic carbon (NPOC)

TOC measurement involves:

  • Oxidizing organic carbon in a sample
  • Detecting and quantifying the oxidized carbon (CO2)
  • Presenting the result in units of mass of carbon per volume of sample