An improved method for isotopic and quantitative analysis of dissolved organic carbon in natural water samples

Abstract

A wet chemical oxidation (WCO) method has been widely used to obtain the dissolved organic carbon (DOC) content and carbon isotope (δ13CDOC) ratios. However, it is sometimes difficult to get high precision results because not enough CO2 was oxidized from the natural water samples with low DOC concentrations. This improvement primarily aims to increase the water sample volume, improve the removal rate of dissolved inorganic carbon (DIC), and minimize the blank DOC from the standard solution. Following the improved procedure, the δ13C ratios of standardized DOC solutions were consistent with their actual values, and their differences were less than 0.2‰. The improved method demonstrated good accuracy and stability when applied to natural water samples with DOC concentrations ≥0.5 mg L−1, with the precisions of DOC concentrations and δ13C ratios were better than 0.07 mg L−1 and 0.1‰, respectively. More importantly, this method saved much pre-treatment time and realized batch processing of water samples to obtain their DOC contents and isotope ratios. HIGHLIGHTS The CO2 peak values of the water samples were within the optimal testing range of the instrument.; Low-temperature nitrogen purging can more thoroughly remove DIC from water samples.; The precision of the DOC concentration in the water samples was better than 0.07 mg L−1.; The precision of the δ13CDOC values in the water samples was better than 0.1‰.;

Keywords

• aquatic environment
• carbon isotope ratios
• dissolved inorganic carbon removal
• dissolved organic carbon
• wet oxidation method