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
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  • Hi nicoled,

     

    Two things contribute to carry over, one is sample preparation and handling, which I dont think is your problem. If you are running a split inlet on your GC, a high concentration standard can leave carry over if your split ratio is too low. It will cause excess vaporized injection to remain in cooler parts of the inlet causing carry over. Also, a pain staking cleaning of your inlet and injection port is probably in order. Another thing is to check how many solvent washes your auto injector performs per sample on the injector syringe. More washes might help. Also, if your solvent happens to be water, then a more intense cleaning regimen for your inlet may be needed, like as in daily.

  • Hello, thank you for such a fast response!

     

    My split ratio is currently 20:1, so I will try increasing it. 

     

    I will also look into cleaning the inlet and injection port, as I don't believe that has been done in a long time.

     

    I am using headspace GC, so there is no solvent to wash with (that I am aware of), but please correct me if I'm wrong!

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