Direct sample introduction EI-MS system

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

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I have been searching for a EI-MS system to obtain an EI-MS mass spectrum, but without the need to include a GC front end, in order to simplify sample preparation and reduce the complexity of the system.

The reason I am looking for this is that the system will be used by an organization whose staff has minimal background in GC-MS spectroscopy, and are not trained in sample preparation techniques of samples for GC.

On the plus side, they have a prep HPLC system with means that the samples whose mass spectrum they want to obtain are already purified (so no need for GC separation).

Since most of you here are much more knowledgeable about these things than me, I'm hoping that one of you knows of a EI-MS system where (a pure) sample can be introduced directly into the mass spec to obtain a EI mass spectrum.

I'm also guessing that such a system would nonetheless require some front end to bring the analytes into the gas phase.


I know similar systems are made by Waters, but the problem is that they us ESI as their ionization source, which would not work for obtaining EI-Mass spectra that can be compared to NIST libraries and used to build EI-MS spectral libraries.

If you know of any such system I would love to hear from you!

If you know that this type of system doesn't exist, I'd also love to hear your thoughts as to why this may not be feasible in practice.

Thank you!
What you are referring to is the use of a "direct insertion solids probe".
With this, the solid sample is loaded into a very small glass vial that is loaded into the probe.
The probe is inserted into the ion source and can be heated to volatilize the sample into the electron beam for ionization.
Most sources can be operated under either electron ionization (EI) for the classic NIST database match OR under chemical ionization (CI) conditions with a large excess of methane or iso-butane or ammonia in the ion source.
Whereas EI is a hard (high energy) process which gives the fingerprint mass spectrum from M+., CI is a soft (low energy) process that produces [M+H]+ which may usually show losses of small neutrals (MeOH, H2, NH3, HCl etc).
Use CI to determine/confirm Mol wt. and then EI to generate the fingerprint spectrum.

Most of the makers have EI/CI mass spectrometers in their line-up.
Thermo and Shimadzu certainly have direct insertion probes as an option on some of their GCMS instruments e.g. http://www.thermo.com.cn/Resources/2008 ... _26945.pdf
You don't even have to buy the GC if sure you don't need it.
We use direct insertion a lot. Can be really useful for compounds too heavy to pass through a GC, but don't ionize by ESI
I don't know if any are still commercially manufactured, but I seem to remember you used to be able to do this sort of thing (direct injection of liquid samples then EI to generate library-searchable spectra) using the old particle beam interface for an LC-MS (LC optional). Of course, there are probably more modern techniques that have supplanted particle beam like the aforementioned probes... it was a technique not without issues.

https://www.sciencedirect.com/topics/ch ... ticle-beam

HP (now Agilent) used to make a PB interface (the 59980B) for their 5989A LC-MS.
You can purchase an Agilent single-quadrupole MSD mass spectrometer without a gas chromatograph. Scientific Instruments Services (SISWEB.com) has a direct incretion probe for the Agilent MSD. It required that the GC not be attached. This would be my recommendation.

In many respects, using a direct incretion probe can be more difficult than using a GC. One of the primary problems is the use of TOO MUCH sample. The sample is usually but into a vessel that resembles a short meltingpoint capillary. When you do this, you will be using too large of a sample and contaminate your instrument very quickly. If you can see the sample, you have too much.

For this to work, the sample must be volatile, just like in GC/MS. The sample cannot be thermally labile.

The better way is to insert the vessel with the closed end out. Make a dilute solution (ug / uL). Put 2 to 5 uL on the outside of the vessel and let the solvent evaporate. Then put the probe into the ion source. You will need to practice. Start with a very dilute sample and then slowly increase the concentration until you get the desired signal.

Good luck!
Regards;
David

O. David Sparkman
Consultant-At-Large
The best and most effective MS probes are of Agilent
A) The Thermal Separation Probe
https://www.agilent.com/en/product/gas- ... tion-probe
and
B) QuickProbe
https://www.agilent.com/en/product/gas- ... -ms-system

In these websites you can learn why or please write me

Aviv Amirav
amirav@tau.ac.il
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