Baseline plateau GC/HS injection

[thw214]

During GC/Headspace runs lately I have been seeing a "plateau" where the baseline rises at around 2.4 min, flattens out and then falls back to where it originated at about 3.4 min. This is occuring during my water diluent injections and when any other solution water based is injected. I am not seeing it if I inject a blank vial through the headspace or on a direct injection not using the headspace on the same columns. I have eliminated the column as the source by trying 3 or 4 different ones. It looks to be coming from the headspace. I have changed out the sample loop and sample probe, and nothing has changed. I am running the USP 467 Residual Solvent method on a G43 column (30m x 0.53 mm x 3.0 um). The GC conditions are as follows:

Chromatographic Conditions
HP 6890 GC with G1888 Headspace
G43 capillary
Flow: 4.0 mL/min
Inlet: 140°C Split Ratio: 5:1
Detector: 250°C
Oven: 40°C, 20min to 240°C@10°C/min, 20min


Headspace Parameters(USP<467> set 1)

Oven: 80°C Loop Fill: 0.5 min Vial Size: 20 mL
Loop: 85°C GC Cycle Time: 70 min Inj/vial: 1
Tr. Line: 85°C Loop Eq Time: 0.1 min Shake: Low
Vial Eq: 60 min
Inject: 1.0 min
Press. Time: 1.0 min

Any suggestions would be appreciated.

[chromatographer1]

Clean or replace your transfer line.

best wishes,

Rod

[thw214]

Thanks, any recommendations on a cleaning procedure.

[aldehyde]

http://www.chem.agilent.com/Library/Sup ... F03008.pdf headspace steam clean procedure.

[thw214]

Thanks. I have tried several steam cleanings. Does anyone know of any procedures aimed at specifically cleaning the transfer line?