General MS Service Information
We offer most of the ionization methods common to organic mass spectrometry
Some ionization methods may be used to generate positive and negative ions as well while others will not. Some ionization methods easily allow for high-resolution experiments to obtain molecular formulae but some combinations will work badly or not at all. Furthermore, the mass analyzer employed (sector, time-of-flight,...) is setting limits to resolution and mass range. Finally, some methods may be combined with coupling to a chromatographic technique and some are not suitable to do so. See equipment section and below for details.
Which ionization method for which type of sample?
Some ionization methods may be used to generate positive and negative ions as well while others will not. Some ionization methods easily allow for high-resolution experiments to obtain molecular formulae but some combinations will work badly or not at all. Furthermore, the mass analyzer employed (sector, time-of-flight,...) is setting limits to resolution and mass range. Finally, some methods may be combined with coupling to a chromatographic technique and some are not suitable to do so. The table below will give an overview of useful combinations based on the actual instrumentation of MS@OCI HD.
|Ionization Method||Typical m/z Range||Analyte Polarity||Ion Polarity||Accurate Mass*||Chromatography Coupling*||Tandem MS*|
|Electron Ionization (EI)||1-1000||low to medium||+||yes||GC-MS||no|
|Field Ionization (FI)||1-1000||low to medium||+||no||GC-MS||no|
|Field Desorption (FD) and Liquid Injection Field Desorption Ionization (LIFDI)||50-5000||low to high and ionic||+||no||no||no|
|Laser Desorption/Ionization (LDI)||50-1500||low to high and ionic||+ / -||yes||no||yes|
|Matrix-Assisted Laser Desorption/Ionization (MALDI)||300-100,000||low to high and ionic||+ / -||yes||no||yes|
|Atmospheric Pressure Chemical Ionization (APCI)||100-2000||medium to high||+ / -||no||LC-MS||no|
|Electrospray Ionization (ESI)||100-10,000||medium to high and ionic||+ / -||yes||no||yes|
|Direct Analysis in Real Time (DART)||180-2000||low to high and ionic||+ / -||yes||no||yes|
* Based on our actual instrumentation.
Guidelines for the use of this facility
- Always use MS in combination with other spectroscopic methods and never use other spectroscopic methods without comparing their results with mass spectra.
- Do not wait until your work comes to the end until you start ordering mass spectra. Decomposition of your samples might be faster than you. Furthermore, it is not amazing to try out all methods in order to get some molecular ion from your waste.
- Please, tell us as much as you know about your sample because the correct choice of an ionization method is an important prerequisite for the reliability of MS results.
- Do not deliver big flasks containing the world´s reserves of your precious compound. Typical routine MS needs some micrograms of sample. Therefore, 0.1-1 mg is really enough for easy handling. Alternatively, solutions of your compound from 0.1-2.0 mg/ml are fine.
- Dirt gives a spectrum of dirt. Mixtures may be analyzed but samples that contain inorganic salts, tar, lubricants, grease, oil, and softeners all together won´t be welcome.
- Do you really need HR-MS or did it just sound more professional to you? Every useless HR-MS is wasting time that might have been enough to produce three nominal mass spectra for you or your colleagues!
- Miracles need some time. If you assist our daily routine business, there will be spare time for special measurements and development of better methods.
- Still questions? Try to find the answer from this website or visit us to discuss your problem.
Requesting an Analysis
- You will obtain a printed form at the entrances of our lab (INF 274/-1.02). Please, use one form sheet per sample and only use the actual version of it to avoid confusion.
- You may also download form sheet.pdf to print it yourself.
- Please fill in carefully as much as you know about your sample because the correct choice of an ionization method is an important prerequisite for the reliability of MS results. If you are not sure about your choice, please ask one of us.
- People from outside the faculty and first-time customers will have to contact us in any case before placing an order.
What instruments are operated at this facility?
The facility is currently operating
- one quadrupole ion trap mass spectrometer (Finnigan LCQ)
- one time-of-flight instrument for EI, CI, FI/FD/LIFDI, GC-MS (JEOL AccuTOGCx)
- one time-of-flight instrument for LDI and MALDI (Bruker Autoflex Speed)
- one Fourier transform ion cyclotron resonance mass spectrometer for ESI, MALDI, and DART (Bruker Apex Qe).
For details, please refer to the equipment page.
How long will my spectra be stored?
MS data are stored for at least five years at our facility. So there should be sufficient time to finish a PhD thesis with all spectra available beyond end of work. You may obtain spectral plots to your needs.
By referring to the file names, all spectra can be correlated to the instrument they have been measured on. See Equipment page for file naming conventions.
How to cite experimental details concerning my mass spectra?
Beyond the instrument used to acquire a mass spectrum, some basic experimental information has to be cited to allow reproduction of results by others. The table summarizes such basic parameters. If you don't feel sure about what the conditions have been, please come and ask one of us, especially in case of experiments using methods such as MS/MS, LT-FAB, ... you should not publish your results without having contacted us before.
Written typical experimental procedures or assistence in writing of such can be obtained on request. Please contact use to ask for this kind of support.
Basic Experimental Conditions Should Include ...
|Energy of primary electrons (usually 70 eV, may be less), sample introduction (direct probe, reference inlet, GC)|
|Reagent gas (often isobutane), positive or negative ions, sample introduction (direct probe, reference inlet, GC)|
|Type of field emitter (generally activated 13 um tungsten wire), sample introduction (direct probe, reference inlet, GC|
|Type of field emitter (generally activated 13 um tungsten wire), eventually emitter current.
In case of LIFDI measurements, type of transfer capillary and concentration of sample solution are required (ideally 0.1-0.2 mg/ml).
|Solvent and eventually added acids, bases or buffers, approximate flow of liquid and sheath gas pressure, type of sample infusion (only syringe pump at the moment), ion polarity.|
|Sample holder (stainless steel, in rare cases nickel coated), positive or negative ions, settings of laser power, sample preparation|
|Matrix compound, sample preparation, positive or negative ions, linear or reflector, eventually type of sample holder.|
|DART gas helium, temperature of DART gas, positive or negative ions.|
|In addition to the above list: ionization method, give experimental and calculated m/z, in case of more complicated isotopic compositions indicate the isotope you refer to (e.g. C10H2010B79Br: exp. 229.0845, calc. 229.0878), eventually resolution, type of mass reference compound.|
|Ionization method (EI, FI), type of GC column, temperature program, split/splitless injection|
|Collision gas, collision energy in laboratory frame of reference, scan mode of the mass analyzer.
SORI-CID on ApexQe: frequency offset, pulse length, excitation power.
Download an Ionization Method Selection Guide and others tools.