6890 GC contamination

[hrunes]

Does anyone have a suggestion on how to resolve contamination seen when a direct injection is performed? The contamination does not appear to be coming from the GC since it is not observed when I run the temperature program without an injection. When an injection is run, the contaminant reappears. I have tried changing the syringe, solvent and waste vials, autosampler vials, and swabbing the needle guide with solvent. All of the new vials and syringes tried have been pre-rinsed with solvent. Any suggestions would be greatly appreciated!

[Mark]

hrunes,

Possibly a contaminant in your solvent itself? Also possibly (not as likely) you are washing something off of the the liner that may be contaminated? I have seen this myself (the liner thing) especially if you are injecting large amounts of non-volatile analytes or "tarry" kinds of samples.

Regards,
Mark

[Consumer Products Guy]

Help us help you by letting us know what happens when you try manual injection of solvent only.

[hrunes]

We have replaced the liner and septum and cleaned out the inlet (I have not changed the gold seal recently however). We have tried injections of several solvents (the sample solvent and a second solvent). I will have the analyst try a manual injection...good suggestion. This method has some serious problems which I'm working with the analyst to correct. For example, they were not running a septum purge and only rinsing the syringe once with solvent after an injection. I'm wondering if there might be other components of the inlet that are contaminated.

[hrunes]

Yesterday the GC analyst ran some manual water injection, followed by DMF injections, followed by water injections (water is the sample injection solvent--definately not ideal). No contamination was seen in any of the manual water injections, but it was observed in all DMF injections. Today when the analyst ran water blanks using the autoinjector, no contamination was observed. I suspect that the DMF, which is presumably a better solvent for the contaminant, is stripping off some of the contaminant somewhere in the injection port when it is injected. I have suggested that after every sequence we run a series of DMF injections, followed by some water blanks to verify that no contamination will be present when we run the next sequence.