• 8 Common Gas Chromatography Mistakes

GC, MDGC

8 Common Gas Chromatography Mistakes

Aug 18 2014

If you're new to Gas Chromatography and looking for some helpful tips, here are 8 common mistakes you'll want to avoid: 

1) Incorrect gas flow rates to a flame ionization detector

If the flow rates are not correct the FID can give an incorrect response for a sample. The gas flow rate to the detector should be optimised according to the manufacturer’s recommendations. A typical ratio is 10:1 (air:hydrogen) producing rates of the order 300 mL/min air to 30 mL/min hydrogen. It is good practice to heat the detector to its operating temperature and to allow it to equilibrate before turning on the detector gases. If the detector does not light, check the flow rates; don’t rely on the instrument settings. If the detector still does not light, the air supply can be reduced to 150 mL/min to light the flame and then be slowly increased to the correct value.

2) Heating a column without any carrier gas flow

This is a simple way to damage a column. Always check that the carrier gas is on and flowing before the heat to the Gas Chromatograph (GC) oven is turned on. The carrier gas should not be turned off until the oven has cooled down.

3) Running out of gas

Making sure that there is sufficient gas for the GC runs. It is poor practice and can be costly to run out of gas - read the article, 5 Gas Management Tips for GC, for some useful advice on gas management.

4) Flooding the injection liner with sample

If the sample volume injected into the GC is too large for the liner, backflash can occur that can result in spurious chromatogram peaks and repeatability problems. Injection volumes should take into account the temperature of the inlet and the type of solvent being used. There can be a considerable difference in the gas volumes generated by different solvents when a sample vaporizes after injection.

5) Leaky septum

A septum is a consumable and should be inspected and changed regularly. It can leak after repeated use leading to pressure problems. Using a damaged septum can also lead to blockages if the septum breaks up. Make sure the correct type of septum is used for the application and that it is installed correctly.

6) Column not conditioned

New columns should always be conditioned before use. This not only improves the column efficiency, but also helps to prolong the life of the column. For more tips on making a GC column last longer take a look at 5 Ways to Extend a Gas Chromatography Column’s Life.

7) Using the wrong syringe

There are many different types and sizes of GC syringes. Consider the application and sample size before selecting the syringe type and volume. For example, trying to use a large volume syringe for a small sample volume can easily lead to problems including flooding of the inlet.

8) Preventative maintenance not carried out

This applies to all analytical instrumentation. Preventative maintenance is usually the lowest cost option compared to replacing broken parts. A simple daily and weekly schedule can identify problems before they happen.

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