Total organic carbon (TOC) quantification: Effect of presence of inorganic carbon (IC) and volatile organic compounds (VOCs)
Young‐Jo Kim, Eun‐Sik Kim
Abstract
Total organic carbon (TOC) is a global standard for water quality, however accurate measurement can be compromised by inorganic carbon (IC) and volatile organic compounds (VOCs). We evaluated two TOC methods - TC-IC (total carbon minus IC), and NPOC (non-purgeable organic carbon) - under varying pH and inert gas purge conditions to minimize these biases. It was found that acidifying samples to pH < 2 and using sufficient purge time are critical to remove IC and improve TOC accuracy. Increasing purge time from 10 to 160 s corrected an overestimated TOC (from 110 % to ∼100 % of the true value) in a carbonate standard. With 0.1 mg/L VOC solutions, NPOC and TC-IC results agreed within ∼10 % for most compounds, although highly volatile organics (e.g., styrene, formaldehyde) showed relatively larger variations. In samples containing both VOCs and significant inorganic carbon, TC-IC tended to underestimate TOC, while NPOC required extended purging to avoid positive biases. These findings indicate that TOC measurement accuracy strongly depends on IC content and VOC volatility. Maintaining pH below 2 and providing sufficient purge time are therefore essential to minimize IC interference. These guidelines are expected to improve TOC monitoring reliability in waters containing VOCs.