Chrysene-d12 inherently erratic?

[Peter Apps]

34 C is certainly low for ethyl acetate as a solvent, so you move to higher oven temperatures should improve things.

When I see a starting or finishing temperature that is not a round number I suspect that the optimisation might have been done by small increments in the temperature, and if 34C does work better than 35C there is a very likely to be a problem with robustness.

Peter

[Yama001]

I have run into the issue James mentioned, although perylene-d12 was the culprit. If you see a forest of mass peaks around the main ion in full scan, that is likely part of the problem.

[JMB]

Here is the oddest part - re-injection of the same solution from the same vial under the same conditions, sample or standard, will usually give excellent results, with the Chrysene-d12 coming in right where it should be.

It would be interesting to see a comparison of the molecular ion region, [M+/-5]+. of the -d12 in its good and bad occurrences.

However, you may now be under the gun time-wise, so if you cannot, that's OK.

JMB

[01310040231]

How do you store the Chrysene-d12 (it should be at room temperature and you have to make sure it does not evaporate). Also, make sure that you do not have any percipitate in your internal standard container.

[Bigbear]

I do 525 using EA as the solvent. I inject 1ul into the injection port @ 250C / pulsed splitless with my oven @ 80C for 0.5 min. I then ramp @ 70C/min to 160, then ramp@12C/min. My first compound is 2 nitro-m-Xylene eluting @ ~ 2.9 min.

[whdees]

when all else fails, RTFM...Read The Freakin Method... "mass spectrometer must be capable of electron ionization at a
nominal electron energy of 70 eV".

I had tried pretty much everything else, so I set it to 70, and so far, so good... we'll see how it does in the long term, but for now, it seems to be OK.

thanks for all of your help, guys!

[Peter Apps]

What did you have the ionization energy set at ?

I can't think of a way that a different ionization energy (on its own) could generate results that are eratic from rum to rum.

Peter

[whdees]

factory default was 25...and the default repeller voltage was 0.0, so maybe the factory settings aren't exactly optimal...I'm still learning this new gear, having been a Hewlett Packard fanboy for 20 years.

I don't understand how that one setting could cause the problem I was seeing either, but I had reached the point of poking things at random just to see what they would do... a year from now I'll laugh about this, but honestly I can't say I'm having much fun...

to H*&^ with it, let's go skydiving!

[cat4lyst]

what a read

[whdees]

sadly, this issue does not appear to be resolved after all... more to come in the near future.

[whdees]

so this issue does finally appear to be resolved... the emission current default was changed to 50 (for some reason), but a factory applications specialist told me to cut it down to less than 25, and to reduce the gain setting to 1 X 10^5...won't pretend to understand the physics, and still don't know why the default was 50, but setting it between 15 and 22 seems to give good repeatability across the board... my RPDs for all compounds are quite good, the sensitivity is very nice, and I'm finally getting usable results... yay!

it's about frikkin time.....

[James_Ball]

so this issue does finally appear to be resolved... the emission current default was changed to 50 (for some reason), but a factory applications specialist told me to cut it down to less than 25, and to reduce the gain setting to 1 X 10^5...won't pretend to understand the physics, and still don't know why the default was 50, but setting it between 15 and 22 seems to give good repeatability across the board... my RPDs for all compounds are quite good, the sensitivity is very nice, and I'm finally getting usable results... yay!

it's about frikkin time.....

Emission current of 50 was making the filaments quite hot I imagine and it does make for quite a bit more breakdown of the molecules. I know my new Agilent 7000 defaults to 35 and that is plenty hot.

[whdees]

so this issue does finally appear to be resolved... the emission current default was changed to 50 (for some reason), but a factory applications specialist told me to cut it down to less than 25, and to reduce the gain setting to 1 X 10^5...won't pretend to understand the physics, and still don't know why the default was 50, but setting it between 15 and 22 seems to give good repeatability across the board... my RPDs for all compounds are quite good, the sensitivity is very nice, and I'm finally getting usable results... yay!

it's about frikkin time.....

Emission current of 50 was making the filaments quite hot I imagine and it does make for quite a bit more breakdown of the molecules. I know my new Agilent 7000 defaults to 35 and that is plenty hot.

thanks, that sounds entirely logical.... still baffled why the default was set so high in the first place. I think the system could stand a bit of idiot-proofing. This ain't the first time I've had ID-ten-T problems