Nitrogen/Protein Determination of Spirulina Algae by Dumas Method

Importance of the Topic

Spirulina is a cyanobacterial biomass widely used as a dietary supplement due to its high protein content and valuable micronutrients. Accurate determination of nitrogen and derived protein content is crucial for nutritional labeling, quality control and compliance with regulatory standards. The Dumas combustion method delivers rapid, automated and eco-friendly analysis compared to conventional techniques.

Study Objectives and Overview

The primary aim was to evaluate the performance of the Dumas method using a FlashSmart Elemental Analyzer for nitrogen and protein quantification in spirulina powder. A secondary goal was to compare helium and argon as carrier gases in terms of accuracy, repeatability and operational cost.

Materials and Methods

• Sample preparation: 200–250 mg of spirulina powder weighed in tin capsules and analyzed in 10 replicates.
• Combustion protocol: dynamic flash combustion using pure oxygen in an autosampler.
• Gas flow path: combusted gases pass through copper reduction, CO₂ and H₂O traps, GC column and are detected by thermal conductivity detector.
• Calibration: nicotinamide standard (22.94 % N) with K factor method; verification using aspartic acid as unknown.

Used Instrumentation

• FlashSmart Elemental Analyzer configured for CHNS and nitrogen/protein analysis
• Thermo Scientific MAS Plus Autosampler with oxygen supply
• EagerSmart Data Handling Software for automatic report generation and protein calculation
• Thermal Conductivity Detector and GC separation column
• Standards: nicotinamide, 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBOT), aspartic acid

Results and Discussion

• Nitrogen content measured ~10.80 % N, yielding ~67.5 % protein (factor 6.25) using both helium and argon.
• Repeatability was high with relative standard deviations below 2 % in all cases, meeting official method criteria.
• No memory effects observed, confirming complete combustion and detection.
• CHNS analysis with argon showed carbon ~47.2 %, hydrogen ~6.9 % and sulfur ~0.61 %, demonstrating multi-element capability.

Benefits and Practical Applications

• Enhanced throughput and automation reduce labor and error compared to Kjeldahl.
• Flexibility to switch to more cost-effective carrier gases such as argon.
• Single-instrument solution for simultaneous analysis of multiple elements.
• Ideal for food, supplement and quality assurance laboratories.

Future Trends and Applications

• Broader adoption of carrier gas alternatives to mitigate helium shortages.
• Integration with laboratory information management systems for streamlined data workflows.
• Development of advanced detectors for trace element analysis in complex matrices.
• Expansion of method applications to novel biological and agricultural samples.

Conclusion

The Dumas combustion method on the FlashSmart Elemental Analyzer provides reliable and reproducible nitrogen/protein data for spirulina. Argon proves to be an effective carrier gas alternative to helium, without compromising accuracy. This approach meets official standards while delivering significant operational advantages.