Measurement of TOC and TN in Marine Water Algae Culture Solution

Significance of the Topic

Microalgae cultivation in seawater presents a cost-effective route to biomass production and sustainable resource utilization.
Managing nutrient concentrations such as carbon and nitrogen is critical for optimizing growth, productivity, and biochemical composition in algal cultures.
Accurate determination of total organic carbon (TOC) and total nitrogen (TN) in high-salinity environments is essential to monitor culture health, nutrient uptake, and metabolic status.

Objectives and Study Overview

This application note evaluates the simultaneous measurement of TOC and TN in seawater-based microalgae culture solutions using a Shimadzu TOC-LCPH analyzer paired with a TNM-L unit.
Seawater from the Sea of Japan was spiked with potassium hydrogen phthalate and potassium nitrate at concentrations of 0, 25, 50, 100, and 150 mg/L to assess method accuracy and linearity.

Analytical Methodology and Instrumentation

The system employs combustion-type TOC analysis with acidification and sparging for organic carbon separation, followed by NDIR detection of CO₂, and chemiluminescence detection for TN achieved through high-temperature catalytic oxidation.
One-point calibration curves were established at 150 mg/L for both TOC and TN standards.

Instrumentation

• Shimadzu TOC-LCPH total organic carbon analyzer for microalgal biomass measurement
• Shimadzu TNM-L total nitrogen measurement unit
• TOC/TN catalyst
• Potassium hydrogen phthalate (Wako, JIS Special Grade) as TOC spike
• Potassium nitrate (Wako, JIS Special Grade) as TN spike

Key Results and Discussion

Spiked samples at 25, 50, 100, and 150 mg/L exhibited measured values within 1–3% of nominal concentrations despite ~3% NaCl content.
Calibration curves for both TOC and TN yielded correlation coefficients of R² = 0.9999, demonstrating excellent linearity.
No significant interference from coexisting salts was observed, confirming the method’s robustness in high-salinity matrices.

Benefits and Practical Applications

• Direct, simultaneous TOC and TN analysis in saline samples without dilution
• Minimal sample pretreatment and rapid throughput
• Capability to measure both dissolved and suspended fractions, including algal cell suspensions
• Low sample volume requirement (10–20 mL), suitable for lab-scale research and QA/QC

Future Trends and Opportunities

Integration with automated online sampling systems for real-time culture monitoring.
Expansion of TOC/TN analysis to other marine biomass and environmental water studies.
Development of miniaturized, high-throughput analyzers for rapid screening in bioprocessing and quality control.
Coupling with stable isotope labeling to elucidate carbon-nitrogen metabolic flux in microalgae.

Conclusion

The Shimadzu TOC-LCPH combined with the TNM-L unit offers a reliable and efficient platform for accurate simultaneous measurement of TOC and TN in high-salinity microalgal culture solutions.
High linearity, minimal salt interference, and low sample volume requirements make this approach well suited for research, process monitoring, and quality assurance in algal biotechnology.

References

No external literature references were cited in the original application note.