Shoulder/ broad peak shape after subsequent runs

Question

After changing liner and o-ring, peak shape was symmetrical for the first run but gives a shoulder peak or broad peak after subsequent run for 8860 Gas Chromatography System. Why is this so? and is it normal for the yellow latch that keeps the liner in place to be very tight when locking it into place?

Dr. Know · Accepted Answer

Shoulder or broad peaks can come from a variety of issues. 
 
 Check the split flow, it should not be zero. 
 Have you checked for leaks? 
 Is the goldseal ok and undamaged? 
 Is the liner's O-ring ok and not squeezed 
 Did you also change the septum? Is it too tight? 
 Is the height of the column in the liner/injector ok? Maybe it moved. If it's too high, you will get broad tailing peaks 
 Does the liner volume fit the injection volume? 
 How does a methane injection look like? 
 
 Those are the starting points. 
 Regards, 
 Norbert

Dr. Know · Answer

First of all, the injection temp for an aqueous injection is far too low. The evaporation water will coll down the liner severely and then maybe you'll get some water condensation in the liner. This condensation would activate the liner and could lead to tailing peaks. It could also activate the start of the column more by additional phase degradation by the more water condensate than necessary. Increase T inj to 270-300 &deg;C. 
 Use an extra deactivated liner like our UltraInert liners for better performance.

jchmiel · Answer

Hi, 
 Based on the inlet parameters you listed, our Vapor Volume calculator shows that you are at roughly half of the liner volume.

Increasing the temperature up to 300C would still keep the vapor volume below 600 uL, which is well below what Restek states for that particular liner

(Please ignore the liner that I selected in this tool. It is the closest we have to the volume and dimensions of the Restek liner that you're using.) 
 
 Thanks.

Shoulder/ broad peak shape after subsequent runs

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