AWWA ACE95256

As with any laboratory analyses, sample collection and preservation techniques are essential to obtaining good TOC data. Two procedures are particularly important for TOC analyses: pre-rinsing the filter papers before sample filtration and pH adjustment to 2. In addition, knowing which method will be used for analysis is helpful in interpreting results. Some studies have led to the conclusion that persulfate-ultraviolet oxidation underestimates TOC concentrations, as compared to combustion-infrared results. Also, the approach to using a particular method can be different for different laboratories. For instance, combustion infrared instruments measure total carbon, then inorganic carbon and obtain TOC by difference. To minimize the translation in error to the TOC value, some laboratories will "decarbonate"--or remove--inorganic carbon before analysis. The water industry should expect some variation in data as normal. Data collection, however, should begin several months before the ICR and the D/DBP Rules become effective to allow potential glitches to be worked out of the TOC sample collection and analysis procedures. This pre-regulatory sampling time will also allow systems to become familiar with variation in their TOC data.