Positive chemical ionisation on Shimadzu QP2010Ultra

[u0008355]

Dear all, I am contemplating buying a Shimadzu QP2010Ultra with EI and PCI (to determine the mass of the molecular ion).
The quote the company gave us was for a Shimadzu with two separate sources, an EI one and a PCI one. They told me they were not sure if the PCI source could perhaps also be used in combi mode as an EI source (by switching off the reaction gas, but they were not sure about the potential drop in sensitivity and if there might be software limits of doing this). They told me that if I wanted to work in combi mode I would have to get an EI + PCI + NCI source, and that this one could be used as a combi source for EI and PCI, but that it would also imply a drop in sensitivity in EI mode compared to a dedicated EI source. Does anybody have any experience with this? Ideally I am looking for a solution so that I could do EI and PCI without having to switch sources, as that seems like quite a hassle...

[BZK]

Hi, I have from more than 7 years a Shimadzu QP2010 equipped with EI, PCI and NCI source. The NCI source can work in mixed mode but, as correctly answered you from Shimadzu, drop in sensitivity by comparison with EI source. This is due to a very narrow hole between filament and target electrode. The hole of EI source is several time bigger because in this mode the reagent gas is not present. With a big hole and reagent gas inside the filament can easily to be damaged to a very big electron emission. This is the reason for narrow hole into PCI/NCI sources.
The drop in sensitivity can be from 5 to 10 times respect EI+ alone.
From my point of view if you need anyway chemical ionisation you must buy EI+ for general use and NCI for NCI and PCI mode.

[u0008355]

Thanks for sharing your experience! Couple of weeks I also went to look at a demo of a Thermo ISQ, and I am a little tempted to go for that one now, especially with it's vacuum interlock system, so that one can very easily change the source from an EI to a PCI source, without having to vent the system... Also, changing the source looked so much easier than with the Shimadzu... (price was the same as the Shimadzu) Tricky choices... Anybody experience here with using a Thermo ISQ for both EI and PCI work? Is it a reliable and robust system?

[ICKK]

Hi, I have from more than 7 years a Shimadzu QP2010 equipped with EI, PCI and NCI source. The NCI source can work in mixed mode but, as correctly answered you from Shimadzu, drop in sensitivity by comparison with EI source. This is due to a very narrow hole between filament and target electrode. The hole of EI source is several time bigger because in this mode the reagent gas is not present. With a big hole and reagent gas inside the filament can easily to be damaged to a very big electron emission. This is the reason for narrow hole into PCI/NCI sources.
The drop in sensitivity can be from 5 to 10 times respect EI+ alone.
From my point of view if you need anyway chemical ionisation you must buy EI+ for general use and NCI for NCI and PCI mode.

Hi,
I have a GCMS QP2010, my enquiry about getting different responses using NCI ion source.
As you stated, NCI ion source allows us to select any of SCI, NCI and SEI mode. I have injected same amount of sample at the same day and got different peak area in order NCI < SCI < SEI (i can send you a file contains all chromatograms and spectra). As I am aware, using NCI source should give a better response under negative ionization mode and less response under SEI and SCI, am i right?
Many thanks for your time.

[BZK]

Yes, you hare right. The NCI ion source give less ion response compared to SCI or (much more less) to EI. This is due mainly to very narrow hole into NCI and SCI sources (locate under filament) compared to EI source. This narrow hole is necessary to keep a relatively high pressure of collision gas into the source only while high vacuum is present in all other parts of vacuum chamber.
Regards NCI and SCI ion sources the first is less capable to produce high abundance of ion due to thermodinamic effects but is highly selective for electron capture chemical species.
At the end, as stated before, to fully use of QP 2010 both EI and NCI sources are necessary. SCI only if you have money to waste.

Regards

Robertino Barcarolo

[ICKK]

Yes, you hare right. The NCI ion source give less ion response compared to SCI or (much more less) to EI. This is due mainly to very narrow hole into NCI and SCI sources (locate under filament) compared to EI source. This narrow hole is necessary to keep a relatively high pressure of collision gas into the source only while high vacuum is present in all other parts of vacuum chamber.
Regards NCI and SCI ion sources the first is less capable to produce high abundance of ion due to thermodinamic effects but is highly selective for electron capture chemical species.
At the end, as stated before, to fully use of QP 2010 both EI and NCI sources are necessary. SCI only if you have money to waste.

Regards

Robertino Barcarolo

Thanks a lot Robertino for the quick and informative reply… very much appreciated

I am aware that NCI source is a semi-closed type of ion source and the pressure in the ion source is about 1 to 10 Pa, while CI is a closed type and EI is an open type.

And I do believe that acidic compound and compounds containing electronegative groups give better selectivity and sensitivity using NCI source and that’s what I was trying to get by injecting a carboxylic acid standard. I have the NCI source installed and the standard was checked on its three modes (NCI, SCI and SEI), but the results were reversed as I stated before NCI < SCI < SEI. Would you please send me your email so I can send you some files to explain the output data.

The other thing I would like to check with you please, SCAN vs SIM, again I am getting less peak area applying SIM mode while should be the reverse as I believe. I have read other posts which stated similar problem and they suggested checking the tune file which I did, but no improvement was obtained.
Thanks

[BZK]

Hi, (give the name...)..
step by step..as stated before yes, electron negativity groups give high response rate in NCI mode and the selectivity is comparable to ECD detector (but not the sensitivity).
With the NCI ion source operated in different mode the results aren't comparable in therms of ion current to the specific ion sources. In case of EI+ mode the ion current, due to narrow hole, is at leas 10 times lower compared to the standard EI source. Regards to the ion current (higher as absolute values) in NCI, SCI and lower in EI mode the difference is due to the presence of gas inside. The 70 eV electron energy, produced by the source, react with gas and produce high ion current. Only reaction gas products are used to ionize at LOW energy the incoming GC molecules even if the product of reaction gas/molecules give low peak area. BUT the ion current inside ion source remain high and the filament dead much more early than EI mode due to high density of electrons involved.
Regard scan/sim peak area the answer is clear. Scan mode use most of time to collect ions from low to high M/Z, keep all togheter in ONE point ang give ONE total ion current point.
Sim mode keep ONE M/Z, repeat a defined number of time the same mesure and give ONE point of total ion current. To go in details the discussion became complicated and long but the sum of ion current produced in scan mode is even higher than sim mode produced on the SAME conditions.
If you need my mail no problem. Send me a private message an i give it.
The discussion is in any case interesting to the forum and in my opinion can be proceded here.

Robertino Barcarolo

[ICKK]

Hi, (give the name...)..
step by step..as stated before yes, electron negativity groups give high response rate in NCI mode and the selectivity is comparable to ECD detector (but not the sensitivity).
With the NCI ion source operated in different mode the results aren't comparable in therms of ion current to the specific ion sources. In case of EI+ mode the ion current, due to narrow hole, is at leas 10 times lower compared to the standard EI source. Regards to the ion current (higher as absolute values) in NCI, SCI and lower in EI mode the difference is due to the presence of gas inside. The 70 eV electron energy, produced by the source, react with gas and produce high ion current. Only reaction gas products are used to ionize at LOW energy the incoming GC molecules even if the product of reaction gas/molecules give low peak area. BUT the ion current inside ion source remain high and the filament dead much more early than EI mode due to high density of electrons involved.
Regard scan/sim peak area the answer is clear. Scan mode use most of time to collect ions from low to high M/Z, keep all togheter in ONE point ang give ONE total ion current point.
Sim mode keep ONE M/Z, repeat a defined number of time the same mesure and give ONE point of total ion current. To go in details the discussion became complicated and long but the sum of ion current produced in scan mode is even higher than sim mode produced on the SAME conditions.
If you need my mail no problem. Send me a private message an i give it.
The discussion is in any case interesting to the forum and in my opinion can be proceded here.

Robertino Barcarolo

Hi Robertino,

I am so sorry for the late reply and many thanks for sharing your precious time and experience.

Yes you are absolutely right, the forum is the right place to share our problems and looking for help!. It is very professional forum and it offers a good value of information plus its members are very helpful.

I couldn’t find a private message function to send you a message, and there’s no attachment function as well to upload my files here

Regards,
Raghad

[ICKK]

Dear Robertino,
Please I need your help with the GC-MS QP2010; MS calibration fails. the files fail to be attached on this forum, and I failed to send them to you as private message.
Please reply at your earliest convenience,
Thanks a lot,
Raghad

[BZK]

Post your calibration file and any usefull info to my job address :

roberto.barcarolo@venetoagricoltura.org

Regards.