Chromatography Forum

Hello,

I'm responsible for the upkeep of the Agilent 6890/5973 GC-MS in our lab. The actual instrument is working perfectly, however there is an issue which keeps creeping up with the autosampler - which is a Gerstel MPS autosampler (made by CTC I think? It's tricky to find information on these as I think they could be rebranded?!).

When running samples, every so often the syringe does not align with the septa on top of the vials and as a result, the needle is pushed into the side of the cap, resulting in a bent needle. We recently had to order a new pack of syringes as we were getting through one every 2 weeks and have moved back to manual injections until the problem is solved.

I've been through the calibration process with the control panel however I am only able to calibrate to each corner position on the vial rack, not individual positions. It has been aligned perfectly with these positions so I am mystified as to why vials in the intermediate positions tend to result in this off alignment.

Having recently inherited responsibility for the machine (I am a synth. chemist primarily but keep things running with the GC!) I believe that this was an issue in the past however nobody is able to tell me how the issue was fixed - indeed when I started back in October we were using manual injections and it is only recently that I've managed to get the robot up and running again. Our Mass spec. department have had a look however cannot offer any suggestions.

To summarise, is there a way to access calibration points for individual positions? It will be time consuming but it's something I'm prepared to do. Other issue could be that the vial tray is warped however as far as I can see with a spirit level this is not the case.

Many thanks for your help in advance,

Geecee

I have had a similar problem when the vial septa were slightly difficult to penetrate - the needle gets a little bit bent, and the bend increases with subsequent vials until the tip is far enough out of line to clip the edge of a cap - then it does the Z fold thing.

Different septa might be needed, but heavy handed crimping can also make soft speta hard to stab through.

Peter

there are cross cutted septas i use for dionex hplc sampling SEC analysis...

i buy them from a german company

"marchery nagel" www.mn-net.com

REFnr.: 702823

Autosamplers should not "miss" the centre of vials although it happens more often if you use vial inserts as the target area gets quite small. I can't comment on the CombiPal (Gerstal) but other samplers I have used often have a user set up to align the first and last sample position and a deep set up . Check also if the sampler can use different trays that the autosampler has identified the right tray type If you've checked the basics , call an engineer ! It must be costing you more than a service visit if you have to go to manual injections

It's been a while but as I recall there is a setting on the controller where you can lower the syringe holder over a vial and using the X,Y,Z adjustments, center the needle over the septa.

Hi Everybody,

Thanks for the replies - we use screw capped vials with septa that you have to put in the lid yourself ( ). Peter- that's a really useful post, as I've noticed some other sample vials in the queue and sure enough that brand (national scientific) have septa which are noticeably thicker (they could even be for LCMS I think). I can completely see how the needle over time could bend and perhaps this is something to look for!

Yep the calibration has been checked, though I'll have a look for the seting where you can centre the needle, as far as I'm aware I could only do this for the centre of the actual vial tray, the inlet and the waste vials rather than specific positions but worth a check. And finally yep maybe an engineer is required - the GC we have is (luckily) a handy bonus which we tend to use more for monitoring reactions or a quick check to confirm product (there are only 10 or so of us in the lab so manual injections dont inhibit throughput too much, plus we are fortunate enough to have teh departmental instruments as well!).

Will let you know how I get on, thanks again!

We use Y-slit septa. the septum itself is pre-slit, but the thin teflon layer underneed isn't. this ensures a good seal and evoids solvent contact with the septum itself.
http://www.la-pha-pack.com/en/produkte.html (exact product is not on the website)