Sample/Standard Carryover

I am running GC 6890 (FID detector) alongside G1888 headspace.

I had noticed 4 of my later eluting peaks got increasingly worse in terms of shape and reproducibility. After running blanks (no injection and also blank vials), it seemed like the cause of this turns out to be carryover. The more blank vials I run after my highest standard, the smaller the carryover peaks become. However, it is not time efficient for me to have to run 3 blanks in between standards in order to get decent peak shapes.

 

 

GC Paramaters

OVEN

Initial: 60C (hold 0.1min) ramp to 300C (12.5C/min), hold 6 min

Carrier gas: Helium 

 

I am using Rxi-624Sil MS column.

 

I have attached chromatograms to illustrate my problem. 

I am relatively new to GC so please do not hesitate to suggest something obvious.

Thanks!

 

Edit to add more instrument parameters:

 

Headspace

G1888 Headspace
Configuration
Headspace Device: Agilent G1888 Headspace Sampler(g1888)
Communications Mode: 10.1.1.102
Serial Number: IT00739016
Vial Size (mL): 20
Handshake Mode: Wait if GC Not Ready
Oven Stabilization Time (min): 1.00
Pressure Units:: psi
Carrier Connection: Front Inlet
Vial EPC: None
Loop Size (mL): 1
Method
GC Cycle Time (min): 40.00
Inject Time (min): 1.00
Loop Equilibration Time (min): 0.05
Loop Fill Time (min): 0.50
Loop Temperature (°C): 135
Oven Temperature (°C): 120
Shake: Off
Transfer Line Temperature (°C): 140
Vial Equilibration Time (min): 30.00
Vial Pressurization Time (min): 0.08
Vial Pressure (psi): 0.00
Carrier Gas Pressure (psi): 0.00

 

GC

OVEN

Initial: 60C (hold 0.1min) ramp to 300C (12.5C/min), hold 6 min

Carrier gas: Helium 

 

FID

Temp: 320C 

Hydrogen flow: 30mL/min

Air flow: 450mL/min

Helim: 45mL/min

attachments.zip
Parents
  • Hi Nicoled:  I would try increasing the temperature of your loop and transfer line.  Seems like your highest boilers might be condensing in the loop/transfer line and then coming out in subsequent runs.  Try going up 10 C on each and see if that fixes it.   I'm not sure how high you can go on either of those.   

    I would also check your GC inlet just to make sure that that hasn't been set really low by accident.  Although the headspace is delivering vapor, the inlet temp still matters.  You wouldn't want your sample condensing (or partially condensing) there either.   

    Good luck!!

Reply
  • Hi Nicoled:  I would try increasing the temperature of your loop and transfer line.  Seems like your highest boilers might be condensing in the loop/transfer line and then coming out in subsequent runs.  Try going up 10 C on each and see if that fixes it.   I'm not sure how high you can go on either of those.   

    I would also check your GC inlet just to make sure that that hasn't been set really low by accident.  Although the headspace is delivering vapor, the inlet temp still matters.  You wouldn't want your sample condensing (or partially condensing) there either.   

    Good luck!!

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