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- Posts: 17
- Joined: Tue Jul 05, 2011 1:19 pm
I've been having a contaminationproblem for about a week now and I can't seem to get rid of it.
Instrument Agilent 7000C QQQ with 7890B GC and AS.
Method:
Injection: 25µL (hexane) solvent vent PTV
Injection speed: 40µL/min
Washes 1 : 3 pre and 3 post acetone
Washes 2 : 2 pre and 2 post hexane
1 Sample wash
starting temp: 40°C (0.85min)
900°C/min to 285°C (12min)
900°C/min to 350°C (2min) cleaning
Venting 75ml/min @ 5psi for 0.75min
splitless transfer between 0.75min and 1.85min
Inlet purge 20mL/min @ 1.85min
Temperature program/Flows:
1.2mL/min
Start 45°C (2.5min)
50°C/min to 280°C (5min)
35°C to 350°C (2min)
column: Agilent PAH Select 15m*0.15mm*0.1µm
I get 6-8 peaks that elute around 200-220°C that all have about the same spectrum. I added the spectrum underneath. If I check with NIST the best match is for di-isopropylnaphthalene, but I don't know where that could be coming from, since it is not something we analyze or is in our standards/samples. The system is used for determination of PAH, PCB and CLB.
The contamination is 'worst' when the system hasn't been used for a while (e.g. overnight or weekend). After the first injection the peaks are still present though at a lower intensity (+-1/10). The peaks also show when injecting air.
What I already cleaned/replaced: Septum, syringe, other type of vials and septa, liner, cleaned inlet base, flushed purge/gas/split lines with MeOH and hexane. Cleaned the split vent trap. Nothing so far has solved my problem.
I know that in the past, while experimenting, I might have had backflash into some lines (25µL injection solvent vent in narrow liner), that's why I cleaned all of the lines.
Any more tips or causes for these peaks are welcome. I'm kinda stuck...
thanks in advance,
Jasn