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 Reply Children
  • I hope it helps!

     

    I know nothing about headspace samplers, so this might be totally normal, but I just noticed the last two lines of your headspace parameters show "Vial Pressure (psi): 0.00" and "Carrier Gas Pressure (psi): 0.00". Is it normal not to have any pressure there? Like I said, I know nothing about headspace analysis, but whenever I have issues with GC, a flow/pressure that got turned off accidentally is a common cause.

  • Although it does say that those parameters have a setpoint of 0, they actually have pressures of 16 and 20 psi respectively! I am also not sure why they appear to be zero, but monitoring the system shows the 'actual' pressures at the appropriate setpoints! It's very curious, but rest assured there is pressure! This is a good observation, I will manually enter the setpoints (since the pressures are reaching that anyway, there should be no harm). 

     

    Thank you!  I am trying the post-run flow and temperature today so fingers crossed!

Was this helpful?