Effects of different storage conditions on the carbon isotopic compositions of dissolved inorganic carbon
Linan Wang, Jun Zhong, Maoliang Zhang, Si-Liang Li, Sheng XuAbstract
The carbon isotopic compositions (δ 13 C and Δ 14 C) of dissolved inorganic carbon (DIC) in water samples are influenced by various storage conditions, but the extent and mechanisms of these changes remain unclear. In this study, we systematically evaluated the effects of storage temperature, pretreatment (filtration and addition of mercuric chloride, HgCl 2 ), and container material (glass vs. plastic) on δ 13 C DIC and Δ 14 C DIC . The δ 13 C DIC values in samples preserved with HgCl 2 exhibited the smallest variation (δ 13 C DICmax −δ 13 C DICmin ranging from 0.7‰ to 1.0‰), followed by those stored under refrigeration (∼4°C; variations of 1.3‰ to 1.4‰). These storage conditions also effectively constrained variations in Δ 14 C DIC over storage periods of up to 60 days in polyethylene terephthalate (PET) bottles. In contrast, comparisons with glass bottles, combined with analysis of PET-derived compounds and associated enzymatic activity, indicated that the degradation of PET-derived compounds provided a plausible explanation for the observed radiocarbon depletion. For long-term storage (>110 days), isotopic fractionation was primarily governed by exchange between DIC and atmospheric CO 2 , attributable to the permeability of PET bottles. This study provides a quantitative, mechanism-based assessment of storage-induced effects on δ 13 C DIC and Δ 14 C DIC , offering practical guidance for minimizing storage-induced uncertainty in carbon isotopic studies.