Separation problem in agilent gcms 7890B ,5977B MSD

[aimee]

Hi all, can anyone of you help me with this new very intelligent new gcms.
I used to run all my samples in old gcms agilent 7890A, but recently my old gc had problem with gc motherboard and cable and still waiting for repair. Thus i need to transfer all my method to the new one, gcms 7890B which i was told that it is thousand time more sensitive than the old one. But the problem is, after i transfer the method, and do some adjustment, eg: lower the flowrate, more split rate, dilute the samples, and adjust the ramping, i still get my compounds didnt eluted in normal order. Yes, the rt will change, but why is the compund didnt eluted in the right order. Tq all

[dblux_]

... Thus i need to transfer all my method to the new one, gcms 7890B which i was told that it is thousand time more sensitive than the old one.

The person who told you that bullshit ... don't trust him Besides 7890B is GC not GC/MS

Take the column from old GC and install it in new GC. Leave the GC method unchanged. This will make your separation very similar to the former one.
The sensitivity is connected with MSD, but you didn't tell us any details if it is the same or different.

[HPLC chemist]

I agree with dblux. Just transfer your column and chromatographic conditions since they are responsible for the separation between the molecules. You will obtain similar retention times (dwell volume between GC's will be different).

Eventually, however you will have to increase your split ratio (and decrease injection volume) so the MSD is not overwhelmed.

[Peter Apps]

Hi all, can anyone of you help me with this new very intelligent new gcms.
I used to run all my samples in old gcms agilent 7890A, but recently my old gc had problem with gc motherboard and cable and still waiting for repair. Thus i need to transfer all my method to the new one, gcms 7890B which i was told that it is thousand time more sensitive than the old one. But the problem is, after i transfer the method, and do some adjustment, eg: lower the flowrate, more split rate, dilute the samples, and adjust the ramping, i still get my compounds didnt eluted in normal order. Yes, the rt will change, but why is the compund didnt eluted in the right order. Tq all

In this context sensitivity has nothing to do with the separation, therefore, like everyone says, keep the chromatographic conditions exactly the same and you will get the same separation. The more settings you change, the less likely you are to get the same separation.

Peter

[Biza12]

Hi all, can anyone of you help me with this new very intelligent new gcms.Transfers Orly
I used to run all my samples in old gcms agilent 7890A, but recently my old gc had problem with gc motherboard and cable and still waiting for repair. Thus i need to transfer all my method to the new one, gcms 7890B which i was told that it is thousand time more sensitive than the old one. But the problem is, after i transfer the method, and do some adjustment, eg: lower the flowrate, more split rate, dilute the samples, and adjust the ramping, i still get my compounds didnt eluted in normal order. Yes, the rt will change, but why is the compund didnt eluted in the right order. Tq all

Take the column from old GC and install it in new GC.

[James_Ball]

Hi all, can anyone of you help me with this new very intelligent new gcms.
I used to run all my samples in old gcms agilent 7890A, but recently my old gc had problem with gc motherboard and cable and still waiting for repair. Thus i need to transfer all my method to the new one, gcms 7890B which i was told that it is thousand time more sensitive than the old one. But the problem is, after i transfer the method, and do some adjustment, eg: lower the flowrate, more split rate, dilute the samples, and adjust the ramping, i still get my compounds didnt eluted in normal order. Yes, the rt will change, but why is the compund didnt eluted in the right order. Tq all

If the elution order is different then most likely the column in the new instrument is a different phase.

As stated above, I would not assume there is so much more sensitivity and just inject with the same parameters as with the other instrument. To be 1000 fold more sensitive you would have to be running something as old as a 5970MS on the old instrument and something like a 7000 triple quad on the new one, but since both are 7890 series GCs I doubt your old instrument is really THAT old.

Using the same column from the old instrument will solve the elution order problem, but if you can get the peaks separated well with the current column just in a different order you can use the new one as it is.