What could be causing this horrible diluent peak shape for my GC-HS residual solvents method?

My method details:


GC Conditions:

  • Column: HP-5MS UI (30 x 0.32 x 1.00)
  • Detector: FID (@ 260C)
  • Carrier Gas: He (2 mL/min)
  • Liner: 1mm straight inert (Restek)
  • Inlet Temp: 230C
  • Split: 10:1
  • Oven Program: 35C, hold for 3 minutes, 15C/minute to 230C

Head Space Conditions:

Vial Size: 20mL (1mL of sample)

Diluent: DMSO

Oven Temp: 145C

Loop Temp: 155C

Transfer Line Temp: 170C

Vial Equilibration Time: 10 Minutes

Vial Pressure Time: 1 Minute

Loop Fill Time: 0.5 Minutes

Loop Equilibration Time: 0.2 Minutes

Sample Inject Time: 0.5 Minutes


I am seeing DMSO elute and drag off the column, and it never returns to baseline. I do not mind the solvent diluent having a poor peak shape since that is expected but because it is so broad I have seen that it  carries over into subsequent injections (see attachment) resulting in a poor baseline. What could be causing this?


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