Recommendations and good practices for dissolved organic carbon (DOC) analyses at low concentrations

Numerous protocols for dissolved organic carbon (DOC) measurements on natural water are used in the literature. An ISO protocol for the determination of DOC exists since 2018, but it is certified for DOC values ≥ 1 mg L^-1, while many publications report DOC values much lower. In addition, this ISO protocol does not include indications on vials cleaning, filtering material, and type of caps and septa to be used. The purpose of this study was to evaluate protocols for measurements of low DOC concentrations (≤ 1 mg L^-1). The effect of the sample container, type of septum, filtration material, nature of acid used for storage, and matrix effects on DOC concentration were evaluated.•The use of glass vials decontaminated at 450 °C or 500 °C for at least 1 h, 0.45 µm hydrophilic polytetrafluoroethylene (PTFE) membranes previously rinsed with 20 mL ultra-pure water and HCl acidification gives the lowest DOC contamination,•Sulfides (ΣH₂S), sodium (Na⁺) or calcium (Ca²⁺) do not induce high matrix effect for the analysis (≤ 10%),•At low DOC concentrations (≤ 1 mg L^-1), the use of pierced PTFE septa with acidified samples induce slight DOC contamination after storage at 4 °C, and dramatic contamination after storage at -18 °C.