Prima PRO and Prima BT Process Mass Spectrometers - Quantitative analysis of bioethanol in biofuel production processes

Importance of the topic

Monitoring and controlling bioethanol fermentation in real time is critical for process optimisation, mass balance closure and efficient scale-up from laboratory to production. Continuous online off-gas analysis provides immediate information on oxygen uptake, carbon dioxide evolution and volatile product formation (notably ethanol), enabling earlier detection of production onset, faster process adjustments and reduced reliance on intermittent offline liquid assays. High precision, stability and low detection limits are therefore essential for accurate kinetic interpretation and robust process control in industrial biofuel and bioproduct manufacture.

Objectives and overview of the application note

This application note evaluates the performance of Thermo Fisher Scientific Prima BT (benchtop) and Prima PRO (process) magnetic sector mass spectrometers for online gas analysis in bioethanol production. Key aims are to demonstrate:

• the suitability of magnetic sector MS for continuous fermentation off-gas monitoring,
• quantitative ethanol measurement in the presence of interfering gases (notably oxygen and CO2),
• the comparative advantages versus quadrupole MS in precision, stability and calibration interval, and
• instrument modifications (glass-lined ion source entrance) to mitigate ethanol adsorption memory effects and improve response times.

Practical results are presented from stability, linearity and response-time tests, together with performance specifications relevant to fermentation control.

Methodology and approach

Quantitative performance was assessed using calibrated gas cylinders and controlled test streams to evaluate accuracy, precision, linearity and dynamic response. Tests included:

• stability tests measuring reference air repeatedly over one week without re-calibration,
• comparative analyses of two inert-gas mixtures spanning a wide mass and concentration range (Helium, Argon, Krypton isotopes, Xenon),
• ethanol linearity tests using cylinders with 100–1,000 ppm ethanol in matrices containing oxygen, carbon dioxide and argon to simulate typical vent gases, and
• dynamic build-up and settling experiments to quantify memory effects when switching between ethanol-containing and ethanol-free streams.

Instrument settings and per-stream optimisation (speed vs precision) were handled through Thermo Scientific GasWorks software. Corrections for oxygen tailing into the ethanol measurement channel were applied based on calibration of the interference.

Instrumentation used

• Thermo Scientific Prima BT benchtop magnetic sector mass spectrometer
• Thermo Scientific Prima PRO process magnetic sector mass spectrometer (e.g., Prima PRO 710)
• Magnetic sector analyzer with high ion acceleration voltage and flat-topped peak response
• RMS multi-stream inlet system for multiplexed reactor sampling
• Thermo Scientific GasWorks software for per-stream method optimisation and display
• Modified ion source with glass-lined gas entrance to reduce ethanol adsorption

Main results and discussion

Magnetic sector versus quadrupole performance

Comparative testing showed magnetic sector MS delivers approximately an order of magnitude better stability and accuracy than a representative quadrupole instrument across a wide mass and concentration range. Key observations:

• Magnetic sector instruments produced flat-topped peaks that are tolerant to small mass-axis drift, improving reproducibility when masses are monitored near the peak plateau.
• Standard deviation and accuracy values from mixed-gas cylinder tests indicate roughly 10× superior performance for the magnetic sector device compared with the quadrupole, which exhibited larger relative errors and higher variability for low-concentration isotopes.
• Calibration intervals for magnetic sector MS are substantially longer (monthly) versus weekly for quadrupole units, reducing maintenance burden.

Ethanol measurement specifics

Ethanol fragments significantly under electron ionization and the most intense ethanol-related ion observed is m/z 31 (CH3O+), not the molecular ion at m/z 46. CO2 isotopes (13C, 17O, 18O) and oxygen tailing cause interference at m/z 45–46 and the oxygen peak tail contributes to m/z 31. The Prima instruments correct for the O2 tailing (quantified during calibration), enabling reliable ethanol quantitation down to low ppm levels.

Linearity and sensitivity

Linearity tests (100–1,000 ppm ethanol in cylinders containing 10% O2, 5% CO2, 1% Ar, balance N2) showed close agreement with certified values (maximum deviation ~6% at 1,046 ppm). Magnetic sector MS demonstrated reproducible ethanol quantitation with detection capability down to ~10 ppm under optimized conditions.

Memory effects and ion source redesign

Ethanol adsorption on stainless steel surfaces in the ion source caused substantial build-up and settling delays, degrading dynamic accuracy when switching sample streams. Replacing the gas entrance channel with a glass-lined path produced dramatic improvements:

• At 100 ppm ethanol: build-up time reduced from ~12 minutes (stainless steel) to <1 minute (glass-lined); settling time reduced from ~90 seconds to <20 seconds.
• At 400 ppm ethanol: stainless steel build-up ~5 minutes and settling >4 minutes, whereas glass-lined entrance reduced settling to <30 seconds and reach steady state to expected values rapidly.

Performance specifications relevant to fermentation monitoring (typical magnetic sector MS):

• Nitrogen, Oxygen: full-scale (0–100%) precision ~0.005 mol%
• Argon: 0–1% range precision ~0.001 mol%
• Carbon dioxide: 0–10% range precision ~0.1% relative or 0.0003 mol% (whichever larger)
• Methanol and Ethanol: 0–1% range precision ~2% relative or 0.001 mol% (whichever larger)

Benefits and practical applications

The Prima BT and Prima PRO magnetic sector systems provide several practical advantages for bioethanol and broader bioprocess monitoring:

• Continuous, high-precision monitoring of O2, CO2 and ethanol for kinetic analysis and process control, enabling earlier detection of fermentation onset and deviations.
• Improved accuracy at low ethanol concentrations (20–100 ppm) after ion source modification, facilitating detection of production onset and fine control of early-stage fermentation.
• Higher sampling frequency from multiple reactors using multi-stream inlets and reduced valve/sample settling times, accelerating process development and screening workflows.
• Reduced offline sampling and less frequent calibrations, lowering operational cost and downtime; normal uptime reported >99.8%.

Future trends and potential applications

Expected directions and opportunities include:

• Further integration of multistream MS with advanced process control and digital twins to enable closed-loop optimisation of fermentation.
• Broader adoption of low-adsorption materials and ion source designs to expand reliable quantitation of sticky VOCs beyond ethanol (e.g., higher alcohols, solvent mixtures).
• Expansion into continuous cellulosic ethanol processes and syngas fermentation monitoring where multi-component gas quantitation at trace levels is required.
• Combining high-precision off-gas MS data with online liquid-phase analytics and PAT tools to accelerate strain selection and scale-up decisions.

Conclusion

Magnetic sector-based Prima BT and Prima PRO mass spectrometers deliver robust, high-precision online off-gas analysis well suited to the demands of bioethanol fermentation monitoring and control. Their fault-tolerant flat-topped peak response, superior stability versus quadrupole systems, and improved ion source design for low-adsorption operation enable accurate ethanol quantitation down to low ppm levels, faster dynamic response and reduced calibration/maintenance effort. These capabilities translate into faster process development, better production control and lower operational overhead in biofuel and biotechnology applications.

Reference

1. Renewable Fuels Association. World Fuel Ethanol Production. (Website data cited in application note).
2. Traynor P., Wright R., Conroy N. Optimization of next generation bioethanol production. Hydrocarbon Engineering. June 2008.