By Anonymous on Tuesday, February 18, 2003 - 04:33 am:
I had a lost in MS sensitivity. I'm trying to understand the reason. I already cleaned the ion source, replaced the septum and liner. Simultaneously the retention time seams to be a litle longer (first it was 9.04 min and now is 9.10 min). One of the "possible" reasons that are mentioned in the books is wrong tune file. I would like to know the effect of a autotune or quiktune in the MS response.
By Andreas on Friday, February 21, 2003 - 06:01 am:
Was there something that proceded this lost of sensitivity, e.g. GC maintainance, shutting down and start up of the MS, or it happened suddenly?
By Anonymous on Tuesday, February 25, 2003 - 02:27 am:
It happened after autotuning de MS.
By R. Plausinaitis on Tuesday, February 25, 2003 - 06:05 am:
I don't work with GC/MS for some time now, but will try to give some suggestions.
Retention time change from 9.04 to 9.10 is perfectly OK and it will not influence sensitivity.
You didn't mentioned, what MS instrument you use, but I have feeling that it's HP59xx. For these instruments Autotune is standard tuning type which will adjust all MS voltages (recommended perform once a week). Quicktune adjusts only some voltages (if I remember right - mass axis, recommended daily). If you used Quicktune all the time before and then used Autotune, "sensitivity" might change. Both these types of tune use "atune" parameters file, so that will not cause "wrong tune file" problem, unless you changed tune file name in the method.
Change of the sensitivity depends what model of the instrument it is, how old it is. Part which most influences sensitivity is ion counting tube (if we spaking about HP instrument).
First thing you can do - check EMV values on older and last Tune reports. If there is substantial increase - there might be a problems with multiplier. Also try to perform autotune several times and check sensitivity inbetween. With all the results try to speak with your service person.
By Anonymous on Tuesday, February 25, 2003 - 09:24 am:
Agilent used to have autotune and max sensitivity tune as separate files, and as the name implies the max sens tune gave higher sensitivity. They then changed to autotune and standard autotune, where autotune is the old max sens and standard is the old autotune. Check to see what tune file was used before, and verify the same file was used last time. Also, tune reports should always be saved and compared if there is a sudden change in sensitivity.