Chromatography Forum

Hi,

I'm looking for better automated sample prep solutions for GC-MS. Our currently prep machine (Gilson GX-271) is demanding more maintance and errors and we have a problem with contamination from samples with amphetamine and coffeine.

This is the currently method:

The sample (1 vial with powder content and 1 empty vial):
- Containing about 5 mg unidentified drug (white powder, pill etc.)
- Adds internal standard 1 (700µl) and then conc. NH3 (80 µl)
- Mixing (aspirates and dispenses the solution) (780 µl 3 times)
- Adds internal standard 2 (700 µl)
- Mixing (aspirates and dispenses) (1400 µl)
- Then the sample will be standing for about 6 min.
- The upper phase will then be transferred to the empty vial (500 µl).
- This vial will then be injected into a GC-MS.

Solvent = Butyl acetate (butyl ethanoate) which is used in the outside and inside rinse stations.

So which sample prep solutions do you recommend?

Can you rinse the needle with an acidic solution between samples? This should wash away these basic contaminants.

Can you rinse the needle with an acidic solution between samples? This should wash away these basic contaminants.

OK, I'm currently using destilled water to wash between sample injections. But this will not affect the pH in the samples? Because our internal standard are sensitive to samples with ascorbic acid for ex (lowers the pH).

Can you wash with acid and then water?

You could take an acidic wash solution from a bottle and dispense it into the rinse station to wash the needle. That way you can keep water as the system fluid. You can then rinse with the water to remove all of the acidic solution.

What errors and maintenance issues are you having? Maybe I can give you some pointers.

The problems are contamination of amphetamine/methamphetamine and caffeine between the samples.

And look at the 1st post again.I've updated some info.