Automation of the picoSpin 80 1H NMR benchtop spectrometer for high-throughput determination of the research octane number of fuels

Importance of the Topic

The research octane number is a key indicator of petrol quality and engine knock resistance. Traditional methods for RON determination, such as CFR engines or gas chromatography, are time-consuming and resource intensive. Developing a rapid, automated approach using benchtop NMR spectroscopy addresses the growing demand for high-throughput fuel analysis in industrial quality control and research laboratories.

Objectives and Study Overview

This work aims to automate sample preparation, injection, and acquisition on a picoSpin 80 1H NMR benchtop spectrometer for rapid RON determination. Integration of a GERSTEL MultiPurpose Sampler and MAESTRO control software enables a fully automated workflow. Multivariate chemometric analysis, including PCA and PLS, is applied to classify fuel samples by RON and predict octane values accurately.

Methods and Instrumentation

Samples were processed and analyzed under the following conditions:

• Benchtop NMR spectrometer: Thermo Scientific picoSpin 80 at 82 MHz proton frequency, 34 °C
• Flow cell: total volume 40 µL, active volume 0.2 µL, connected via 80 cm PEEK tubing
• Automated sampler: GERSTEL MultiPurpose Sampler 3 with 1 mL glass syringe and 32-position tray for 10 mL vials
• Control software: GERSTEL MAESTRO version 1.4.2.25, invoking picoSpin acquisition executable
• NMR experiment: one-pulse sequence, pulse length 58 µs, bandwidth 4 kHz, 64 scans, 7 s recycle delay
• Reference: 100 µL tetramethylsilane added on-the-fly, no deuterated solvents required
• Data processing: free induction decays stored (4096 points) and processed in MestReNova 9.0.1; MATLAB R2015b used for PCA and PLS

Main Results and Discussion

The fully automated prep-and-shoot workflow achieved an average cycle time of 7 minutes per sample and supports over 200 analyses per day with minimal manual intervention.

Principal Component Analysis separated high-octane fuels effectively, with clear clustering of RON 98, 99, and 102 samples; RON 95–97 samples overlapped due to similar ethanol content variations.

Partial Least Squares regression based on 47 calibration samples and leave-one-out validation predicted RON with deviations ≤0.5 for over 80% of samples and maximum errors under 1.0, demonstrating quantitative reliability.

Benefits and Practical Applications

This automated low-field NMR approach offers:

• Rapid turnaround: seven minutes per sample vs. 25 minutes (engine test) or 45–90 minutes (GC)
• High throughput and reproducibility for fuel quality control
• Minimal solvent use and no deuterated reagents
• Scalable automation via MAESTRO scheduler and large sample trays

Future Trends and Applications

Potential developments include:

• Integration with GC or GC-MS via switching valves for complementary analyses
• Expansion to other fuel types and additives using advanced chemometrics and machine learning
• Real-time monitoring of refinery streams and on-site field analysis
• Enhanced automation platforms with robotics and remote control

Conclusion

The coupling of a GERSTEL MultiPurpose Sampler with a picoSpin 80 benchtop NMR spectrometer under MAESTRO control provides a robust, high-throughput method for RON determination. Chemometric analysis via PCA and PLS delivers qualitative classification and quantitative predictions with acceptable accuracy, offering a practical alternative to traditional engine and chromatographic tests.

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