Hi Apuetz,
We have the Agilent 7890A-5975C GC-MS combination with the Agilent 7693A autosampler systems with two towers. I think that our AS is the same as yours.
When we bought the system, we wanted to use the advertised features of the AS system, which included things such as the addition of an internal standard as you mentioned.
After two years plus of frustration including discussion with both local and national Agilent staff including at 2 ASMS conferences, the current situation is that if we were to use the autosampler in any way other than to simply inject the sample, we need to use the GC Chemstation software and use the easy prep sample module (extra cost) to try to accomplish the addition of internal standards and the like. We would have to use the GC Chemstation software to prep the sample and then use Mass Hunter or MSD Chemstation to inject the sample. Definitely not ideal. If you have just GC then the easy sample prep could simplify things BUT I would have to be convinced that these operations actually work in practice
To respond specifically to your question, I did try to use the sandwich capability of the autosampler to add an internal standard to analyte that was already in the syringe. I found it very unreliable. I was able to carry out the physical operation of adding the internal standard into the syringe already containing the analyte but found that the first few injections were consistent and then the signal for my internal standard would drop drastically and stay dropped - my analyte was tetradecane and the IS pentadecane so I didn't expect this. This behavior was very consistent on repeated sequences even to the injection number at which the IS signal would drop.
I didn't get any real answer from Agilent as to why this was happening and in the end put it down to another advertised feature of the autosampler that didn't work as promised.
Apuetz, let me know if you need help with how to physically do the sandwich feature.
Anyone from Agilent reading this - any ideas how to move forward and get this autosampler to work to its potential.
Kevin
