Determination of Carbon, Nitrogen and Sulfur in Plant Tissue

Significance of the Topic

The accurate determination of carbon, nitrogen and sulfur in plant tissue is essential for assessing crop nutritional status, optimizing fertilization strategies and ensuring sustainable agricultural production. These macronutrients are fundamental to protein and enzyme biosynthesis, and their quantification provides critical insights into soil uptake efficiency and plant health.

Objectives and Study Overview

This study showcases the analytical capabilities of the LECO CNS928 macro combustion instrument for simultaneous measurement of C, N and S in dried plant samples. It examines method performance using certified reference materials and evaluates operating parameters such as carrier gas selection and aliquot loop size.

Methodology and Instrumentation

Samples are dried to constant weight (80–85 °C, 2 h), homogenized and loaded into ceramic combustion boats with approximately 1 g of LECO COM-CAT™ combustion aid. Combustion occurs in a pure oxygen environment at 1350 °C. Resulting gases are collected in a ballast and introduced via helium or argon carrier gas into detection cells: non-dispersive infrared for CO₂ and SO₂, and a thermal conductivity cell for N₂. The system supports both 10 cm³ (high precision) and 3 cm³ (extended reagent life) aliquot loops. Analytical workflow includes blank determination, calibration or drift correction using reference materials, and sample analysis with automated autoloader sequencing.

Instrumentation Used

• LECO CNS928 macro combustion C/N/S determinator
• NDIR cells for CO₂ and SO₂ detection
• Thermal conductivity detector for N₂
• Ceramic combustion boats, COM-CAT™ reagent, inert carrier gas supply (He or Ar)
• Automated sample autoloader and software-controlled aliquot loops

Main Results and Discussion

Analysis of LECO and NIST plant reference materials (tobacco, alfalfa, apple leaves) demonstrated excellent accuracy (C, N, S recoveries within certified values) and precision (RSDs typically <0.1 % for C, <0.03 % for N, <0.01 % for S). Helium provided superior sensitivity for nitrogen at low levels, while argon offered acceptable performance. The 10 cm³ aliquot loop yielded the best precision; the 3 cm³ loop reduced gas consumption and extended reactor life without significant compromise in data quality.

Benefits and Practical Applications

• Simultaneous quantification of three key macronutrients in a single run
• High throughput with minimal sample preparation and automated sequencing
• Cost-effective single-point calibration using pure compounds
• Applicability for agronomy, quality control and environmental monitoring laboratories

Future Trends and Opportunities

Emerging developments include integration of CNS analysis with digital data platforms, miniaturized autosampling systems for field applications, expansion to multi-element detection and coupling with isotope ratio analysis. Adoption of greener carrier gases and further automation will drive enhanced efficiency and sustainability.

Conclusion

The LECO CNS928 instrument delivers robust, precise and accurate determination of carbon, nitrogen and sulfur in plant tissues. Its flexible configuration, simple calibration protocol and high throughput make it an ideal tool for agricultural diagnostics, research and industrial quality assurance.

References

• LECO Corporation. Determination of Carbon, Nitrogen and Sulfur in Plant Tissue, Application Note, Form No. 203-821-592, 2022.
• LECO CNS928 Operator’s Instruction Manual.