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Low sensitivity for higher MW components in GC

Question asked by acraig on Jan 14, 2020
Latest reply on Apr 20, 2020 by james_jenkins

Hello,

 

I am using an Agilent 7890B with HP-1MS column SN19091S-913E.  Periodically (~25%), when installing a new column, i run into issue where components eluting >35minutes have severely reduced sensitivity. GC parameters at the bottom using splitless injection.  

 

i.e, one standard will have component not detected, while a standard that is 2x concentrated will have area count 100.  I am using multiple equipment and verify there is no problem in standard prep because the other equipment have normal sensitivity and linearity.

 

I have reviewed common problems and solutions here...

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1) Standard too cold/compounds precipitate.

      - Unlikely to be cause because other equipment is operating fine at the exact same time using same standards.              -Also, previous column installed on the now troublesome equipment showed normal sensitivity.

2) Componds are not properly vaporizing in the injection port.

      -Removed glass wool from the liner and reinjected same standards.  No improvement to sensitivity.  Are there other ways to see if this is happening?

3) Column has contamination.

      -Issue has been found multiple times when installing brand new column, probably not the root cause.

4) There is a cold sport somewhere.

      -Not sure if changing column could introduce cold spot somewhere somehow.

5) High column bleed

      -Not observed

6) Purge valve (split) time set too short.

      -This would be a method problem.  This method shows normal sensitivity on other equipment and has on this equipment before replacing column.

7) Missing insulation around injection port.

      -Insulation present.

 

GC parameters below.

 

Injector temp: 300C

Detector (FID): 350C

Gas Flow: H2 40mL/min

                 Air 400 mL/min

           Makeup (He): 20 mL/min

           Constant Pressure: 20 PSI

 

60C start temperature for 1 min

10C/min to 300C

2.5C/min to 325C

325C hold for 20 mins.

 

I have just reinstalled the same column backwards with the outlet side now at the inlet, and cut off ~1foot of the inlet and installed at the outlet.  I am reinjecting same standards to see if maybe problem was on inlet side of column.

 

Since this problem occurs regularly frequently when installing new columns, does anyone have advice what i could try for troubleshooting next?

 

Thank you in advance.

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