General strategy for GC problems
- ◄ Problem solving advice
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- It is much easier and cheaper to prevent problems than to fix them
- Consider the instrument as three units: injector, column and detector
- Attempt to isolate the problem unit
- Adopt a logical approach
- Write everything down
- ◄ If you have persistent problems
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- Get a second opinion
- Seek advice
- Recheck everything
- Remember the simple and obvious
Problem area 1 - Injector
- ◄Injector advice
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- Do not heat until purged with oxygen- free gas (10 volumes)
- Always note injector and detector ends
- Always cut end of column after passing through ferrule
- Consider column dimensions and phase
- Consider the use of pre-column
- Set correct flow rate using linear carrier gas velocity
- Do not overheat column unnecessarily
- Use good quality ferrules and change as needed
- Support the column cage in the oven
- ◄Carrier gas
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- always use high quality gases
- use and regularly change gas filters
- use good quality cleaned tubing
- ◄Septa
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- choose high quality low bleed septa
- change septa regularly
- consider tip style of syringe needle
- ◄Syringe
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- use the correct one for the injector
- clean the syringe regularly
- never inject less than 20% full scale
- ◄Inlet liner
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- consider inlet liner design
- change inlet liner regularly
- ◄Other items to consider
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- column connection
- injection technique
- injection temperature
- solvent used
- split flow
- splitless time
Problem area 2 - Column
- ◄Column advice
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- Do not heat until purged with oxygen-free gas (10 volumes)
- Always note injector and detector ends
- Always cut end of column after passing through ferrule
- Consider column dimensions and phase
- Consider the use of pre-column
- Set correct flow rate using linear carrier gas velocity
- Do not overheat column unnecessarily
- Use good quality ferrules and change as needed
- Support the column cage in the oven
- ◄Things that can deteriorate your column
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- Very large volume injections
- Dirty samples
- Very acidic/basic samples
- Poor gas management
- Overheating
- ◄Restoring your column
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- Remove 50 cm to 1 m from the injector end of the column
- Turn the column around and re-condition it
- Wash the column
- ◄Chromatograms showing the effect of conditioning
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Compounds:
1. Decane
2. 4-Chlorophenol
3. Decylamine
4. Undecanol
5. Biphenyl
6. PentadecaneReference run using BPX5 GC column
Carrier gas has been turned off at 300°C for 2 hours
After reconditioning for 2 hours
After further reconditioning at 370° C for 6 hrs
Reference run using BPX5 GC column
- ◄Column conditioning
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Choose a conditioning temperature 20°C above your method temperature, or choose the Maximum Specified Temperature - whichever is the lower.
Remember: the lower the temperature, the longer your column will last.
- ◄Column storage
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- Store the column so it can’t be scratched
- Seal the column ends (with septa)
Problem area 3 - Detector
- ◄Detector advice
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- Regularly check and adjust gas flows
- Periodically clean the detector
- Consider detector temperature
- Ensure correct positioning of column in detector
- Do not push column into FID flame.