Shimadzu TALK LETTER Vol. 1

Importance of the Topic

Accurate measurement of total organic carbon (TOC) is a cornerstone in environmental monitoring, water and wastewater management, and bioprocess development. Ensuring reliable TOC data underpins decisions in process control, quality assurance, and research fields ranging from drinking water treatment to biofuel production.

Objectives and Study Overview

This document introduces an accuracy control function integrated into TOC-Control L software to enhance the reliability of TOC analyses. It also demonstrates a practical application: direct measurement of TOC in suspended microalgae cultures to monitor growth and carbon balance without sample pretreatment.

Methodology and Instrumentation

The study employs a combustion-based TOC analyzer to oxidize organic carbon fully, with two IC-handling approaches:

• Difference method: measure total carbon (TC) and inorganic carbon (IC), then calculate TOC = TC − IC.
• NPOC method: acidify sample (pH ≤ 3) to convert IC species to CO₂ and purge with inert gas, then measure TC as TOC.

Instrumentation details:

• Analyzer: Shimadzu TOC-L CPH total organic carbon analyzer
• Catalyst: Standard oxidation catalyst
• Calibration: One-point curve using 1000 mgC/L potassium hydrogen phthalate
• Sampling: Autosampler with schedule files for up to 10 calibration curves and automated reanalysis if control criteria are violated

Results and Discussion

Accuracy Control Function:

• Users define upper and lower limits for accuracy control samples.
• If measured concentration deviates beyond set limits, the system automatically recalibrates and reanalyzes affected unknown samples.
• Schedules support batch runs: multiple calibration curves, accuracy checks at start and end.

Microalgae Application:
Daily TOC measurements of culture suspensions (Sample 1) and supernatants (Sample 2) were used to calculate cellular organic carbon. Turbidity served as a biomass index. Results showed:

• Dynamic changes in TC, TOC, and IC over an eight-day growth cycle, with TOC/TC and IC/TC ratios reflecting physiological shifts.
• Screening of five microalgae strains revealed species-dependent organic carbon uptake and release patterns, and IC measurement identified calcifying species.

Benefits and Practical Applications

The accuracy control function and robust TOC analysis enable:

• Enhanced data reliability for environmental compliance and QA/QC.
• Automated routines that reduce manual intervention in high-throughput laboratories.
• Direct monitoring of biomass and carbon balance in algal biofuel research.
• Screening of microbial or algal cultures based on organic carbon dynamics.

Future Trends and Opportunities

Emerging directions include integration of AI-driven diagnostics for proactive calibration management, coupling TOC analysis with real-time sensors for process intensification, and application to novel bioproduct screening. High-throughput and miniaturized TOC platforms may further expand use in drug development, biomanufacturing, and environmental forensics.

Conclusion

The introduced accuracy control function in TOC-Control L software significantly improves measurement reliability by automating calibration checks and reanalysis. Coupled with a powerful combustion-based analyzer, it supports direct TOC determination in complex suspensions such as microalgae cultures. This capability advances routine water analysis and cuts across research in biofuel production, environmental science, and industrial quality control.

References

• Data provided by Professor Shiraiwa's research laboratory, University of Tsukuba