6850/6890 FID Ignition Problems - Flame will not light or will not remain lit.

Significance of the Topic

Flame ionization detection (FID) is a cornerstone technique in gas chromatography for quantifying organic compounds. Reliable ignition of the hydrogen flame ensures stable baseline and accurate measurements. Failure to light or maintain the flame disrupts analyses, generating downtime and impacting data quality.

Objectives and Study Overview

This application note outlines common causes of FID ignition failures on Agilent 6850/6890 systems and provides a structured troubleshooting workflow. It aims to help analysts identify root causes and restore reliable operation.

Methodology and Instrumentation

The overall approach involves sequential verification of operating conditions:

• Temperature control: maintain FID oven at least 20 °C above the final GC oven temperature, with an optimal setting around 300 °C and minimum of 150 °C.
• Gas supply integrity: confirm purity (≥ 99.999 %), adequate pressures (carrier/makeup 80–100 psi, air ≥ 80 psi, hydrogen ≥ 60 psi), and leak-free connections.
• Igniter functionality: observe glowing igniter during ignition sequence.
• Flow rate validation: measure carrier, makeup, hydrogen, and air flows using an independent flow meter and the FID flow adapter part number 19301-60660.
• Detector configuration: set the LIT OFFSET threshold to trigger re-ignition when background current falls below typical 2 pA.

Used Instrumentation

• Agilent 6850/6890 Gas Chromatograph equipped with FID.
• Bubble or electronic flow meter for independent flow measurements.
• FID flow adapter part number 19301-60660.
• Electronic leak detector and handheld controller for jet blockage testing.

Main Results and Discussion

Application of the workflow highlights key factors affecting FID ignition:

1. Gas purity, pressure, and leak-tight pneumatic fittings are essential to maintain stable flow and ignition.
2. Proper FID jet condition and correct gasket installation prevent flow restrictions.
3. Accurate flow control via EPC modules requires periodic verification against independent measurements to detect module calibration drift or defects.
4. Adjusting the LIT OFFSET value can prevent unnecessary re-ignition attempts when background current deviates from default thresholds.
5. Blockage in the jet can be diagnosed by monitoring unintended flow on the makeup channel during a manual jet test.

Advantages and Practical Applications of the Method

This systematic troubleshooting framework offers:

• Faster resolution of FID ignition issues, minimizing instrument downtime.
• Enhanced reliability and reproducibility of quantitative analyses.
• Improved confidence in flame stability and baseline consistency.

Future Trends and Potential Applications

Emerging developments may further improve FID performance and diagnostics:

• Integration of automated flow verification sensors to continuously monitor detector flows.
• Advanced diagnostic software with real-time alarm triggers for ignition anomalies.
• Implementation of machine learning algorithms to predict maintenance needs and optimize LIT OFFSET settings.
• Enhanced materials and coatings to reduce jet fouling and improve long-term stability.

Conclusion

Maintaining reliable ignition of the FID on Agilent 6850/6890 systems hinges on tight control of temperature, gas purity, flow rates, and leak-free connections. A methodical troubleshooting workflow enables swift identification of ignition failures and supports consistent analytical performance.

References

No external references specified.