TOC and TN Measurements of Seawater

Importance of the Topic

Monitoring total organic carbon (TOC) and total nitrogen (TN) in seawater is critical for assessing organic pollution and eutrophication risk in marine environments. Reliable TOC and TN data support pollution control, ecosystem health studies, and compliance with environmental regulations.

Objectives and Study Overview

This study demonstrates a rapid, direct method for simultaneous TOC and TN determination in seawater using Shimadzu’s TOC-LCPH combustion analyzer equipped with the TNM-L total nitrogen unit. The primary goals were to evaluate accuracy in high-salt matrices and validate linearity and recovery across a range of analyte concentrations.

Methodology and Instrumentation

Seawater collected from the Sea of Japan was used as the sample matrix. Spiked samples were prepared by adding:

• Potassium hydrogen phthalate for TOC at 25, 50, 100, and 150 mg C/L
• Potassium nitrate for TN at the same concentration levels (mg N/L)

The TOC-LCPH analyzer with TNM-L unit and TOC/TN catalyst performed high-temperature combustion. Key measurement settings included:

• Acidification and sparging for TOC removal of inorganic carbon
• Single-point calibration at 150 mg C/L and 150 mg N/L
• Direct injection of undiluted seawater (~3.5 % NaCl)

Main Results and Discussion

Calibration curves for TOC and TN showed excellent linearity (R = 0.9999). Measured values for unspiked seawater were 1.05 mg C/L and 0.21 mg N/L. Spiked sample recoveries closely matched added concentrations:

• 25 mg/L spike: 25.8 mg C/L TOC, 24.7 mg N/L TN
• 50 mg/L spike: 51.7 mg C/L TOC, 49.1 mg N/L TN
• 100 mg/L spike: 102.1 mg C/L TOC, 101.2 mg N/L TN
• 150 mg/L spike: 151.4 mg C/L TOC, 152.8 mg N/L TN

These results confirm accurate quantitation without dilution or matrix‐matching, highlighting minimal salt interference.

Benefits and Practical Applications

The combined TOC-LCPH and TNM-L system offers:

• Simultaneous TOC and TN analysis in a single run
• Direct measurement of high-salt samples without pretreatment
• High throughput and reduced laboratory workload
• Reliable data for marine pollution monitoring and research

Future Trends and Potential Applications

Advances may include automated field‐deployable analyzers for in situ monitoring, integration with online sample collection systems, and extension to other saline matrices (e.g., brines, industrial effluents). Coupling with complementary detectors could expand multi-elemental profiling.

Conclusion

Shimadzu’s TOC-LCPH analyzer with TNM-L unit enables accurate, efficient simultaneous determination of TOC and TN in seawater without sample pretreatment. This approach supports robust environmental assessment and simplifies laboratory workflows.

References

Shimadzu Corporation. Application News No. O63: TOC and TN Measurements of Seawater. First Edition: November 2017.