contamination problem (liner exchange) - need help

[Mr.Brown]

Hello

We are using the OPTIC-4 Injector unit from ATAS with our Shimadzu QP2010 ultra.
I am in the middle of method development were i am using splitless injection.

I have some issues with contaminations and I am trying to find the source of the contamination.
The base line looks fine if I just run the temperature program with no injection.

I get a few contaminant peaks when injection N2 (mostly silanyls)
- tested two different syringes,
- also cleaned syringes with (MeOH GC-Grade, deion H2O HPLC Grade, n-Hexane GC-Grade, Acetone GC-Grade)

When I inject 1 µL MeOH (GC-Grade) i get a lot of contaminant peaks (mostly silanyls but also some others)
- tested different MeOH bottles, all MeOH show the same contaminant peaks

I replaced the liner (A100001) and septa.
In the liner there was clearly some dirt.
Unfortunately with the new liner when running the temperature program (no Injection)
I get now a worse base line than before with the old liner (very noisy, several peaks, and much higher baseline at higher temperatures)
- tried to conditioning the new liner (320°C for 30 min, 0,5 mL/min column flow, 1:100 split ratio, 2.5 mL/min purge flow)

I am desperate and gladly accept any suggestions you have for me.

[Peter Apps]

What column are you using ?

When you put in the new liner, did you wear gloves or handle the parts with forceps. If not what you are seeing on your blank programme run is probably finger grease, which will take while to disappear.

Peter

[Mr.Brown]

Hello Peter

Thanks vor your reply

I am Using a ZB MultiResidue-1 from phenomenex.
I always wear nitril gloves or cotton gloves, however i do not touch the liner, i use forceps (clean them with n-hexane befor i use them)
I have a MS conected to the GC the clear peaks i see are some silanyls
the noise background seems to be due to some Masses in the range 55-57, 70-73 and 85

[Peter Apps]

The two sources of the contaminant peaks are the inlet septum and the column phase. You might need to try a different type of septum. Do you have oxygen and moisture scrubbers on your carrier gas supply ?

Peter

[BMU_VMW]

Have you checked the tip of the injection-needle?
If there is even the smallest hook it will rip your septum and small septum particles will end up in your liner causing a lot of peaks.

[Mr.Brown]

The two sources of the contaminant peaks are the inlet septum and the column phase. You might need to try a different type of septum. Do you have oxygen and moisture scrubbers on your carrier gas supply ?

Peter

i use a highe temperature resistance septa (Restek - Shimadzu Plug Premium Non-stick), so far i had no problems with this type of speta.

We have a oxygen and moisture scrubber.
If there is a problem i should see an increased peak for oxygen and H2O when doing an MS moisture check
but the MS check looks fine.

[Mr.Brown]

Have you checked the tip of the injection-needle?
If there is even the smallest hook it will rip your septum and small septum particles will end up in your liner causing a lot of peaks.

The tip of the injection needle looks fine, so no ripping should be happening.

[Mr.Brown]

Now cut of roughly 20 cm of the column (injection side)
I also heated the injector to 600 °C for 30 min (no column atached)
column flow rate 1 mL/min, split 1:100, purge flow 3 mL/min.

Now the base line looks even worse (but is getting better with each GC run, no injection, just the temp program)

[Peter Apps]

I hope that you took the septum out when you baked the injector.

What type in inlet liner do you have ? Siloxane deactivated galss wool can generate contaminant peaks.

Presumably you are using an autosampler (nearly everyone does) - try pre-rinsing the sample vial, and clean out or replace the solvent wash vial(s) and refill them with clean solvent.

Peter

[Mr.Brown]

I hope that you took the septum out when you baked the injector.

What type in inlet liner do you have ? Siloxane deactivated galss wool can generate contaminant peaks.

Presumably you are using an autosampler (nearly everyone does) - try pre-rinsing the sample vial, and clean out or replace the solvent wash vial(s) and refill them with clean solvent.

Peter

Nop i kept the septum in it as well as the liner.
Standard procedure from OPTIC-4 manual. (The Septum side gets to a max of 400 °C or so)

I use a standard straight split/splitless line (no glass wool) A100001 (ATAS GL).

Yes i use an autosampler.
But at the moment i do no injections, i only look at the empty runs with no injection at all



no injection
Splitless, sampling time 1 min
50°C hold 1 min
10°C/min to 125°C
15°C/min to 170°C
200°C/min to 290°C hold 4.5 min

you will agree this should not look like this

[Peter Apps]

Standard procedure or not, the deactivation of the liner will have broken down at 600C (which is nearly red hot), and the septum will have suffered at 400C. Did you replace them after the bakeout ?

Problem is, you may have bled cooked liner and septum into the septum purge and split lines, form where they will diffuse back into the gas stream to cause endless problems.

It looks like you have baseline drift due to column bleed, as well as some contaminants, have you checked for leaks lately ? How tall is the peak from about 1 ng of what you want to analyse ?

Peter

[Mr.Brown]

Standard procedure or not, the deactivation of the liner will have broken down at 600C (which is nearly red hot), and the septum will have suffered at 400C. Did you replace them after the bakeout ?

Problem is, you may have bled cooked liner and septum into the septum purge and split lines, form where they will diffuse back into the gas stream to cause endless problems.

It looks like you have baseline drift due to column bleed, as well as some contaminants, have you checked for leaks lately ? How tall is the peak from about 1 ng of what you want to analyse ?

Peter

I did not change the Septa or the liner afterwards.
According to ATAS GL the A10001 Liner can be heated up to 600°C with out any problems (manual says the liner stays in the injector during backing). Also according to ATAS GL
the septum should not suffer.

I understand your concerne about bleed into the purge and split lines.
I am thinking about rinsing them with n-Hexane and Acetone to see if they are the problem.

MS Leak Test looks normal

I whant so measure in the range of 0,025 to 1 ng (~ 0,025 to 1 µg/mL --> 5 to 200 µg/kg of sample concentrated via SPE 5g Samples at the end in 1 mL org. solvent)

0.05 ng gives roughly 175 000 peak hight (TIC)

[Peter Apps]

Earlier you mentioned dirt in the liner, which presumably came from earlier samples (it cannot have come from blanks and solvent injections). This suggests some history - what samples and how many have been run through the system previously ?

Peter

[Mr.Brown]

Earlier you mentioned dirt in the liner, which presumably came from earlier samples (it cannot have come from blanks and solvent injections). This suggests some history - what samples and how many have been run through the system previously ?

Peter

thats hard to tell but since the last liner change, roughly 300 samples (headspace, t-BME extracts from food samples, some standards,...)

I rinsed now the injector with acetone and n-hexane and backout once more 500°C for 1 h (with liner inside, and septa, as suggested by ATAS GL technician)

[jss37992]

I would leak check everything. A baseline like that could also mean you have a small oxygen leak.