Eliminate the risks in using Hydrogen as a Carrier Gas in GC Analysis. Hydrogen is widely considered to be the best carrier gas for gas chromatography systems. In fact, ASTM subcommittee D0.204 for Hydrocarbon Analysis strongly recommends hydrogen as the de facto choice for GC laboratories. Other advantages of hydrogen include rapid analysis, greater efficiencies, decreased costs and extended column life. The reasons for choosing hydrogen are undeniable—if you take the correct measure to protect your lab from hydrogen leaks. The ability to safely detect hydrogen leaks in the GC oven is critical to any laboratory using hydrogen as a carrier gas. The new DVLS3 H2 Sensor ensures the safe use of hydrogen in GC analysis. It does this by constantly monitoring the H2 concentrations in the GC oven and automatically switching to an inert gas when typically 25% LEL is reached; this important feature eliminates the risks and at the same time ensures safety.

1. Simply Smart: The Hydrogen Sensor for
Chromatographic Systems
The DVLS3 Simply Smart Hydrogen Sensor
www.davinci-ls.com

2. Content
§ Four reasons for using H2 as a carrier gas
§ Safety measures
§ Hydrogen sensor
§ Principle of operation and measurement
§ Hardware overview
§ Calibration and maintenance
§ Summary
§ Questions

3. Reasons for using H2 as a Carrier Gas
1. Fast Analysis:
§ Fast diffusion rate; 4 times
faster than N2
§ Half as viscous as helium;
higher linear gas velocity and
shorter retention times
2. High Efficiency:
§ Flattest Van Deemter curve

4. Reasons for using H2 as a Carrier Gas
3. Prolonged Column Life:
□ Some applications have a lower elution
temperature, therefore the column life is
longer
4. Cost effective:
□ 3x’s less expensive than its helium equivalent
□ Bottle or generator

5. Reluctant to use H2 as a Carrier Gas?
§ Hydrogen is an Explosive Gas: Undetected gas
leaks can lead to an explosion in the GC oven
§ LEL of hydrogen in Air is at 4%

6. Safety measures
§ Monitor hydrogen usage
§ Safety measures in GC hardware
□ Safety Shutdown: when gas pressure set points
are not met, the valve and heater are shut off
to prevent explosion
□ Flow Limiting Frit: if valve fails in open position,
inlet frit limits the flow
□ Oven ON/OFF Sequence: Fan purges the oven
before turning on heater to remove any
collected H2
□ Explosion Test: GC designed to contain parts in
case of explosion
§ Hydrogen sensor in the oven or
valve box

7. Principle of Operation
Hydrogen Sensor
§ Catalytic combustion by
catalytized resistor or “pellister”
§ Surface of the pellet acts as a
catalyst when hot
§ Exothermal oxidation of
flammable gases
ú 2 H2 + O2 → 2 H2O(g) + heat
§ Temperature rise results in a
change in the electrical
resistance

8. Principle of Measurement
Hydrogen Sensor
§ Compensator pellet is identical but without
catalyst
§ Compensator pellet removes the effect of
environmental factors
§ Measurement circuit: a Wheatstone Bridge
8 13 March 2013

9. Gas sensitivity
Hydrogen Sensor

10. Typical Zero Offset drift with Temperature
Hydrogen Sensor

11. Typical long term zero offset drift
Hydrogen Sensor

12. Typical long term gas sensitivity drift
Hydrogen sensor

13. Hardware overview for a Hydrogen Sensor
for GC applications

14. Sensor installed in the GC Oven
Transfertube through the
oven wall to ensure a
stable temperature

15. Automatic Switch to Nitrogen
After 1% H2 detection, the carrier gas supply is
switched to nitrogen. The system will maintain a
flow through the column.

16. Automatic Stop Signal to GC
After 1% H2 detection, the sequence will stop after
the analysis. No waste of analyses or sample.

17. Alarm messages
After 1% H2 detection a choice of alarm signals:
§ Acoustic alarm
§ Optical alarm (blinking
display)
§ SMS alarm message
17

18. Calibration & Maintenance
§ Zero Point Calibrated Using Air
§ Alarm level Calibrated using Calibration Mixture
§ Yearly or after maintenance or repair

19. Summary (1)
§ Catalytic Pellistor gas specific sensor, linear range
of 0-2% H2 (0-50% LEL)
§ Unaffected by humidity, stable output for long
periods, more resistant to shocks and vibrations.
§ Expected lifetime: over five years
§ Long term stability drift sensitivity: less than 2mV
§ User defined alarm: optical, acoustic and/or SMS
up to 50% LEL

20. Summary (2)
§ Instrument readings: provide real time sensor
readings with alarm levels, channel states
§ Valve : High pressure 3 way solenoid valve
§ Oven operating temperature: up to 450◦C
§ Multiple Sensors: Max 4 sensors individually
controlled
§ Sensor options: temperature, barometer, level,
oxygen or hydrogen as a leakdetector.