Measurement of Total Organic Carbon in Salt- Containing Sediments

Importance of the Topic

Sediment organic matter is a key component in aquatic ecosystems, influencing nutrient cycling and pollutant binding. Accurate quantification of total organic carbon in sediments supports environmental monitoring and ecosystem assessment, especially in samples with high salt content that can compromise analytical instruments.

Objectives and Study Overview

This study presents a workflow for measuring TOC in salt-containing sediment from a brackish environment. It aims to evaluate pretreatment steps including desalination, quantify TOC loss during washing, and demonstrate TOC determination using a combustion-based analyzer.

Used Instrumentation

• Shimadzu TOC-LCPH total organic carbon analyzer
• Shimadzu SSM-5000A solid sample combustion unit
• EDX-7200 energy-dispersive X-ray fluorescence spectrometer

Methodology and Instrumentation

Samples were centrifuged to obtain wet sediment, dried at 105–110°C, and ground to a fine powder. Desalination involved adding ultrapure water and centrifuging twice to reduce chloride levels below 200 ppm. TC was measured by catalytic combustion at 900°C, IC by phosphoric acid decomposition at 200°C, and TOC calculated as TC minus IC. Liquid-phase TOC was determined by NPOC following acidification and sparging.

Main Results and Discussion

Two desalination cycles lowered chloride concentrations to below 200 ppm. TOC loss in supernatants amounted to about 1 % of the sample TOC, requiring minor correction. The dried sediment after desalination exhibited a TOC content of 2.040 % C (143 mgC), with corrected TOC reaching 2.062 % C.

Benefits and Practical Applications

• Rapid analysis time of 6–8 minutes per sample
• Single system capable of both liquid and solid TOC measurements
• Reliable data for salt-rich sediment monitoring and QA/QC in environmental analysis

Future Trends and Applications

Further optimization of desalination protocols may be needed for varying sediment types and salinities. Automation and integration with complementary analyzers could enhance throughput. Applications extend to paleoenvironmental reconstruction, pollutant fate studies, and routine environmental quality assessments.

Conclusion

Effective desalination pretreatment combined with combustion-based TOC analysis provides accurate organic carbon measurements in salt-containing sediments. The TOC-L/SSM-5000A system delivers rapid, reliable results with minimal sample loss.

References

• Sediment Survey Method August 2012, Ministry of the Environment, Water and Air Environment Bureau, Japan