10 Common GC Mistakes

May 28, 2014
By LCGC Editors

1) Not Taking Enough Care at the Inlet

Any leak in GC will cause significant problems with chromatography and the inlet is the most likely area. Don't take the risk of having to troubleshoot a leak, change the septum regularly and make sure the column is correctly installed and leak-free.

2) Turning the oven on before the carrier gas

If there's one thing that will permanently damage a column more quickly than anything else it's heating the column without any carrier gas flowing. Get into the habit of making sure the carrier gas is flowing before you switch on the oven AND make sure the oven is cool before switching the carrier off. When switching the oven off, set the oven temperature to 35oC before switching the oven off as this will cool much quicker.

3) Not programming in column dimensions

Most modern GCs use an EPC (electronic pneumatic controller) to accurately deliver carrier flows and this relies totally on the correct column dimensions being entered by the operator. Make sure anytime you change the column you enter the correct dimensions into the GC or else your flowrate and split ratios will be wildly inaccurate.

4) Not using optimal flowrate for carrier

Each carrier gas has an optimal linear velocity, which gives the best efficiency (Nitrogen c.12cm/sec, Helium c.35cm/sec and Hydrogen 40 - 50cm/sec). To obtain this optimal linear velocity the flowrate is matched to the internal diameter of the column in use. e.g. for a 0.32mm ID column using helium the optimal flowrate will be about 2.0ml/min. If the optimal flowrate is not used, column efficiency can be significantly reduced.

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