GC/Headspace carryover

[Emma.L]

Hello, I am very new to GC and Headspace and I'm looking for some good advice and tips.
I am following the residual solvent analysis from the EP 8.0 2.4.24.
The column I am using has not been extensively used, it has recently been re-installed and the runs following have peaks detected in my blanks.
I ran a blank (water) first followed by a reference solution and followed by another blank. Both blanks before and after the reference solution have peaks.
I have increased some headspace parameters; the transfer line, loop temperatures, vial pressure and purge time to ensure there is no condensation occurring and to push the sample through but I have found no difference.

The instruments I am using are Agilent 7697A headspace and 7890B GC
column I am using is an Agilent DB-SELECT 624UI: 30m, 320u,1.8u
Gas type He
Inlet Mode Constant Flow
Inlet Initial Time 20.00min
Inlet Initial Flow 1.500mL/min
Inlet Initial Pressure 10.0psi

Oven ramp:
Rate degC/min 10.00
Final temp 240
Hold time 20.00
Total time 60.00

Inlet:
split
140degC
split ratio 5.0
Split flow 7.5ml/min
purge flow 0.000ml/min
purge time 0.00(min)
vent pressure 0.000ml/min
vent flow 0.00
septum purge 3.0ml/min

Back Detector:
Detector Type FID
Makeup Gas Type N2
Flow Mode Constant Makeup
FID Temp Setpoint 250(Deg. C)
FID Makeup/Total Flow 30.0(mL/min)
FID LitOffset 2.0(pA)
FID Fuel Flow 30.0(mL/min)
FID Oxidizer Flow 400.0(mL/min)

Headspace set parameters:
Temperature:
Oven 80
Loop /valve 95
Transfer line 110
Time:
GC cycle time 70
Vial equib time 60
Pressure equip time 0.50
Inject time0.50
Vial:
fill at flow to pressure
fill pressure 15 psi
fill flow 50.00mL/min
loop fill ram rate 20psi
loop final pressure 10.05
loop equilibration 0.05
vial size 20mL
shaking on

[dblux_]

Peaks in blanks don't necessarily mean carryover.
Check different water as blank.

Are the peaks from your 2nd blank higher than from 1st blank. If yes, that might be carryover.

[kubowicz.tomasz]

Hello

I'd recommend bake out all heating zones in headspace sampler (loop, valves, transfer line). Put them all to their maximum allowed temperature and leave for 1 hour. If this procedure won't help I would replace sample loop.
And one more thing: for checking if headspace sampler is free from contamination run blank as empty, capped vial (do not use water)
Good luck

Regards

Tomasz Kubowicz