Chromatography Forum

Greetings All,

Could anyone offer me some suggestions. I have a carryover problem.

I am doing static headspace (HS) analysis using a CTC combipal.

I have checked all of my reagents for the analyte. Which all produced "flat" baselines.

I have run an instrument blank, (no injection) the instrument runs through the instrumental method. This produced a "flat" baseline.

The syringe was removed following the injection of a high level standard and cleaned with methanol, this produced the analyte peaks.

Does anyone have a suggestion for me?

Regards,

Tom

Tommy,

Sounds like it is stuck in your inlet, especially if you rinsed the syringe between injections. There are several posts about inlet contamination from large injections where the sample gets up into the split vent and septum purge lines. What is needed now is liner type and volume, injection volume, split or splitless....

Best regards.

AICMM,

We do not believe that the carryover is coming from the inlet. The reason being that we have run instrument blank, (i.e. the syringe does not even enter the inlet, the instrument runs through the method w/o an injection). The instrument results in a "flat" baseline.

Would you have a procedure that would allow me determine if it may be coming from the inlet other than running an instrument blank?

Tom

Tommy,

Try an injection with zero syringe volume after you run your high standard. Needle will still go in but no injection. Should tell you if something is hung up inside the lines or on the bottom of the septa. Still interested in knowing splitless or split, what volume, what liner, what flows, septum purge flow...

Best regards.

Prepare a true blank, a vial sample with everything in it but your analyte and process that sample vial via your method.

If then you see nothing then you can assume it is not from your starting matrix or your inlet. You should then concentrate on your syringe as the source of your carryover.

Unless of course you believe it came from the pipettes or dispenser during sample preparation.

best wishes,

Rod

Set purge the HS-syringe for upto 10minutes with Nitrogen. Heat ipto max temp.

The simplest explanation (based on what you tell us) is that the "carryover" is coming from the methanol. Run Rod's blank, do you still see carryover ?

What is the analyte ?, and what are the analytical conditions ?

{eter

You contamination comes from glass barrel.
Did you try with another syringe?


xxx

Are you using the post-injection syringe flush on the CTC autosampler? Have you set an injection port dwell time? I usually use a 5 sec post injection dwell time to make sure that heavier analytes are baked out of the needle. I have seen a few cases where the side-hole needle has shaved small pieces of septum into the needle during injection, and this has caused some carryover due to compound adsorbed onto the septum particles.