ASTM D8351-22: Elemental Analysis of Biodiesel using MP-AES

Importance of the Topic

This application note outlines a standardized approach to quantify trace elements in biodiesel using microwave plasma atomic emission spectrometry (MP-AES). Accurate measurement of calcium, magnesium, phosphorus, potassium, and sodium is critical for ensuring engine performance, preventing catalyst fouling, and minimizing harmful emissions. This method addresses safety concerns by eliminating flammable gases and reducing operational costs through nitrogen generation from air.

Study Objectives and Overview

The primary goal was to demonstrate the performance of the ASTM D8351-22 method on the Agilent 4210 MP-AES system across five independent laboratories. Key aims included assessing detection limits, calibration linearity, accuracy using certified reference materials, and long-term stability during extended sample sequences.

Methodology and Instrumentation

Sample Preparation and Calibration

• Standards for Ca, Mg, P, K, and Na were prepared at 0.1, 1, 5, 10, and 20 mg/kg in biodiesel solvent.
• Yttrium (20 mg/kg) served as an internal standard, introduced via a mixing tee.
• Continuing calibration verification (CCV) and blank checks were performed to monitor accuracy and drift.

Instrumentation Setup

• Agilent 4210 MP-AES equipped with External Gas Control Module (EGCM), OneNeb Series 2 nebulizer, and double-pass glass cyclonic spray chamber.
• Agilent 4107 nitrogen generator provided plasma gas in most labs.
• Analytical parameters: 3–10 s read time, 60 s uptake delay, auto background correction, EGCM air injection (medium to high) at 0.5 L/min nebulizer flow.
• Autosampler: Agilent SPS 4 for consistent sample introduction.

Main Results and Discussion

Calibration and Detection Limits

• Linear calibration curves were obtained for all analytes over the chosen concentration range.
• Method detection limits ranged from 0.01 mg/kg for Ca to 0.19 mg/kg for P, demonstrating high sensitivity.

Accuracy and Precision

• Recoveries in two reference materials fell within ±20% of certified values, with most elements within ±10%.
• QC standards measured every ten samples over three days showed recoveries within ±10%, confirming stability and robustness.
• Interlaboratory reproducibility was demonstrated across five labs and multiple biodiesel samples (B5, B40, B100 blends).

Benefits and Practical Applications

The MP-AES method offers:

• Enhanced safety by using nitrogen instead of flammable gases.
• Low operational costs due to on-site N₂ generation.
• High sensitivity and reproducibility suitable for regulatory compliance.
• Ability to operate unattended and in remote locations.

Future Trends and Opportunities

Advancements likely to expand the method’s utility include:

• Integration of automated sample preparation and data analytics to increase throughput.
• Miniaturized and portable MP-AES systems for field analysis in remote production sites.
• Extension to additional trace metals and metalloids relevant to emerging biofuels.
• Coupling with separation techniques for speciation studies.

Conclusion

The ASTM D8351-22 MP-AES method on the Agilent 4210 platform delivers a reliable, safe, and cost-effective protocol for elemental analysis of biodiesel and blends. Demonstrated sensitivity, accuracy, and interlaboratory consistency make it well suited for routine quality control in the petroleum and biofuel industry.

Reference

1. ASTM D8351-22: Standard Test Method for Determination of Trace Elements in Biodiesel and Biodiesel Blends by Microwave Plasma Atomic Emission Spectrometry, ASTM International, 2022.
2. Significance of Tests for Petroleum Products: Analytical Methods for Determination of Inorganic Species in Petroleum Products and Lubricants, ASTM MNL1-9th, 2018.
3. ASTM D8322: Elemental Analysis of Crude Oil and Residual Fuels using MP-AES, Agilent, 2011.
4. Agilent MP Expert Software User Guide, Agilent publication 5990-8975EN.
5. Metals in Biodiesel Reference Standards, Agilent website, accessed 2022.