Recently my lab has had some difficulties with an unknown peak that appears on instrument blanks. This peak occurs at around 180 degrees C and with a flow of around 10ml/min using helium it appears around 20 minutes into the run. Heating the inlet and column at 280 appreciably reduces the peak but if the instrument is allowed to cool down and set for a period of time, it recurs larger. Our helium lines are stainless steel, certified clean, with stainless steel regulators and gauges and we also support a getter system. We have 18 GCs, nine of which are on one gas system and nine on a separate gas system. However, this peak occurs on GCs from both systems. Our gas is chromatographic grade helium. We have baked the septa at high temps before use. When we inject a solvent, doesn't matter which kind, the peak gets bigger. We have tried different and new columns and it still appears. We are concerned that there may be something within the GC inlet inside that is contributing to this, such as O rings in the EPC unit. Has anyone else suffered this problem? Please advise.
By Anonymous on Friday, May 3, 2002 - 07:42 am:
What detector are you using? I have heard that there was a problem early on with ECDs and the HP EPC, which was addressed by changing some components in the EPC.
By Anonymous on Friday, May 3, 2002 - 08:00 am:
I would also take out the inlet liners, clean or replace them, and physically clean out the unlet itself using methanol and a brush. Even if this doesn't help, it's a good idea to this routinely. I would also try different type of septum, what could it hurt (sometimes people "condition" a new septum overnight before use. We have two 6890s and four 5890s (4 with EPC) and don't have any contamination issues. Obviously with a flow of 10 ml/min you are using packed column or possibly 0.53 mm columns; if 0.53 mm column, using septum purge will help hold down any contaminants from septa.
By jean on Friday, May 3, 2002 - 08:58 am:
This message is linked to the earlier one of this date and in answer to the above suggestions. We are using FIDs. We have cleaned the inlets with hexane and methanol and have tried alternative septa. Our columns, overall, are .53 but on a .32 column with a flow of 2 ml/min we have also seen the peak.
By Sepulveda on Friday, May 3, 2002 - 03:40 pm:
I recomend you to install an Helium tank just behind of one of your instruments with its respectively traps. That will let you to know if the contamination is in your He lines or somewhere inside your GC.
By Anonymous on Friday, May 17, 2002 - 11:27 am:
The problem could be: carrier gas contam., inlet line contam. (from injection flashback)or split vent volatiles backing into the inlet (more common with splitless injection, especially the 6890). Try to isolate the source. Make blank runs with no injection. Make a blank run after the system has been sitting idle for an hour and then start another run immedately. If the peak is smaller, in the second run, it's the gas or the line. Try lowering the injection port temperature (try 150). If the peak is smaller, the contaminent must be coming from the heated zone. We sometimes heat the top of the injection port and the incoming carrier line with a heat gun to drive off flashed contaminents. Has the split vent line been checked? Also make sure the port between the inside of the injection port and the split vent line is clean. Good luck!
By rRichard Turcotte on Friday, May 31, 2002 - 10:54 am:
I suspect contamination who is trap on your head column when your oven temperature is low.
1-Suspect gas purifier in GC,bypass this trap.
2-Maybe,you have a small leak in your gc,check for it
3-clean your split vent tube
4-try another split valve..contamination
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