Training - GC basic problem solving

General strategy for GC problems

◄ Problem solving advice

• 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

• Get a second opinion
• Seek advice
• Recheck everything
• Remember the simple and obvious

Problem area 1 - Injector

◄Injector advice

• 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

• always use high quality gases
• use and regularly change gas filters
• use good quality cleaned tubing

◄Septa

• choose high quality low bleed septa
• change septa regularly
• consider tip style of syringe needle

◄Syringe

• use the correct one for the injector
• clean the syringe regularly
• never inject less than 20% full scale

◄Inlet liner

• consider inlet liner design
• change inlet liner regularly

◄Other items to consider

• column connection
• injection technique
• injection temperature
• solvent used
• split flow
• splitless time

Problem area 2 - Column

◄Column advice

• 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

• Very large volume injections
• Dirty samples
• Very acidic/basic samples
• Poor gas management
• Overheating

◄Restoring your column

• 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

Compounds:
1. Decane
2. 4-Chlorophenol
3. Decylamine
4. Undecanol
5. Biphenyl
6. Pentadecane

Reference 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

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

• Store the column so it can’t be scratched
• Seal the column ends (with septa)

Problem area 3 - Detector

◄Detector advice

• 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.