Chromatography Forum

We are trying to set up an SPME methode on a Gerstel MPS2 autosampler 'injecting' on a Gerstel CIS septumless injector.
Fiber is a 24Ga that should be suited for this type of injector (http://www.sigmaaldrich.com/catalog/pro ... &region=BE).
Problem is that when the fiber is in the injector the injector is leaking A LOT. The injector has been serviced, all seals have been replaced and yet the problem persists. Obviously I can't find any components in my chromatogram.

Does anyone know what to do?
Is it at all a good idea to use a septumless injector for this purpose or should I prefer a regular injector?

kind regards
BMU

Are you sure that the sharp edge of the square-cut SPME needle is not scratching the polymer seal at the top of the injector ? It is possible to round off the edge by careful use of fine abrasives, but it is probably easier just to use an injector with a septum. Is there a particualr reason that you need to use a septumless injector ?

Peter

Merlin microseal ? Note there are different sizes of seal and you need the large one to avoid damaging it when you use an SPME needle.

@ peter:
we use this injector because the autosampler is suited for SPME and it is a GC-MS/MS.
The other device we have with an MPS2 autosampler and regular injector is a single quad MS

@CE Instr.
we use a gerstel septumless sampling head on an CIS PTV
http://www.gerstelus.com/products.php?prod_id=22

The outer diameter of the needle is the same as the one we use with regular liq injections, so it should seal. Major differences are the time in the injector: seconds for liq and minutes for SPME, and the injector temp.: +/-40°C for liq and 200°C for SPME.

@ peter:
we use this injector because the autosampler is suited for SPME and it is a GC-MS/MS.
The other device we have with an MPS2 autosampler and regular injector is a single quad MS

@CE Instr.
we use a gerstel septumless sampling head on an CIS PTV
http://www.gerstelus.com/products.php?prod_id=22

The outer diameter of the needle is the same as the one we use with regular liq injections, so it should seal. Major differences are the time in the injector: seconds for liq and minutes for SPME, and the injector temp.: +/-40°C for liq and 200°C for SPME.

So there is no analytical reason (i.e. contamination, baseline drift etc) to use the septumless injector.

I would be very surprised if the outer diameters of the needles were the same within the tolerances needed to give a gas tight seal. It is years since I used a CIS - is there a compression adjustment for the cylindrical needle seal ? If so you could try to tighten it, but then you run more risk of scoring the seal with the edge of the needle tip.

You could try threading a septum onto the needle, then adjusting the autosampler VERY carefully to compress the septum against the top of the injector so that it seals above the CIS needle seal.

Peter

So there is no analytical reason (i.e. contamination, baseline drift etc) to use the septumless injector.

No not really, it has been bought this way to prevent septum bleed. the instrument is used for liq injection, but I'm trying to make a SPME methode for odor compounds and this instrument has al the features I need (triple quad, MPS2, Rxi5silMS column), except an injector with a septum.

is there a compression adjustment for the cylindrical needle seal ? If so you could try to tighten it

The injector 'seals' with a teflon ferrule that is possitioned under a nut that can be tightend. I've already done that to the max. If too tight I risk bending the needle.

You could try threading a septum onto the needle, then adjusting the autosampler VERY carefully to compress the septum against the top of the injector so that it seals above the CIS needle seal.

I don't think this is possible since there is a needle-guide on the autosampler. The needle is not protruding so there is no space to put a septum. It is the needle-guide that is touching the top of the injector.

BMU