Carry Over of samples

[ziarehmann]

Hi,

Nowadays i am working on the determination of volatile fatty acids in water and wastewater samples. For that purpose i am doing liquid injection (1 ul, 1:50 split ratio, 1 ml Column flow He) and also headspace gas injection (400ul). The problem what i am facing is the carry from previous samples. For manual injection i am using the Hamilton gas tight syringe.
I get a large amount of carry over between my samples. I tried to run blank samples using water in order to remove the remaining sample but does not seem to work. in order to see whether the sample remains in Column or line or coming from syringe, i also run blank sample without injection and as a result i dont see anything in chromatogram, means the impurity comes from syringe.

Could you please suggest what i can do in order to clean my syring? I tried to rinse it with ethanol/methenol mixture and then with water but does not bring anything. Is there any better way of cleaning the syringe. Is it also possible that apart from syringe, there is contaiminant in the GC liner??

Regards!

[bunnahabhain]

If you have a second syringe handy, try injecting with one syringe, then do a blank injection using the second syringe - this way you can see if the needle port is the place where the contamination resides. If this is the case, you must somehow flush the injection port between injections (I am no GC guy, this is what I would do on a HPLC).

Jörg