Chromatography Forum

Hi everybody,

I'm working on a method to quantificate Methanol in a polimer (poly vinil pirrolidone). I'm using manual headspace (1mL syringe) and I'm injecting 0.5mL of gas phase into a GCMS.
I'm using deuterated methanol as internal standard, 0.1g of polymer and 5 mL of water into a 20mL headspace vial.

The problem is that I found a carryover effect on the peak of methanol.
I'm using SIM at 31-32 m/z and I get a small peak on these masses after the standard...

How can I clean the syringe? I've tried 3-4 washing with water and drying with N2 but it doesn't work..

Do you have any suggestion?

Thank in advance for the help,

Davide

I assume you are using a teflon plunger syringe perhaps with a removable needle.

You should separate the syringe barrel from the needle and plunger.

Then wash and rinse and dry with N2 and HEAT to completely remove residual methanol from the Teflon components of the syringe.

Have you tried using more than one syringe for your stds and samples so you don't have to clean the same syringe over and over?

good luck.

Rod

This is to second Rod. Manufacturers should quit making syringes with these guides which lead people to try cleaning syringes without taking the plunger out.
I mentioned before that it is possible (not proven yet) that the anouncements about ouabain being a new hormone are based on carryover from syringes and injectors.
The syringes used here (metal plunger, removable needle) have not shown any carryover after washing the plunger separatly, then the needle and syringe by drawing alternately liquid and air through via vacuum (dip the needle into the liquid 3x, press a rubber vacuum hose to the other end, dry with the air.......).

menthanol is known to be "sticky". It sticks on pretty much everything and column bleeding, tailing is well-known if methanol is used as solvent.

For the same reason, I guess your analyte, which is methanol, sticks in your system to create carry over. I would suggest you to have either large split flow or large carrier gas velocity to min. the carry-over. This is what we do when methanol is the choice of solvent, but it might be the solution for you in your assay.

In case of using methanol as solvent, the velocity can be set extremely high. for example, the 0.53mm ID column (15M) were set to have 10psi, with average velocity of 160 cm/min and the split flow was set to 50mL/min. Don't be shy and feel free to try various settings in your analysis.

and, Good luck.