Q-TOF (ESIMS) measurements

In electrospray ionization mass spectrometry (ESIMS), samples are vaporized and ionized from a solution at atmospheric pressure before entering the analyzer section of the mass spectrometer as partially desolvated ions after being sprayed in a strong electrostatic field.

This method is particularly suitable for polar compounds soluble in water, alcohols or acetonitrile. Uncharged sample substances are either protonated by these solvents or they form cationic adducts with sodium ions, and more rarely with potassium or lithium ions.

In contrast to the EI and CI methods, the cations required for detection are thus formed chemically and not physically in ESI mass spectrometry. The BRUKER IMPACT II has a wide detection range because multiply charged substrates can also be measured (z = 1,2,3... in m/z). It has a high resolution, i.e. masses can be measured accurately up to 4 digits behind the decimal point.

Cationic compounds (e.g. pyridinium salts) can be detected unassociated and in very low concentrations. Neutral molecules are usually found as sodium adducts [M + Na+]+, i.e., with a mass 23 higher than the organic substrate, and more rarely as protonated species, i.e., with a mass one higher. To calculate the molecular weights to be detected, use the reduced masses ("exact mass" on the order sheet), not those found in the periodic table of the elements.

In the spray chamber of the mass spectrometer, small droplets of these sample solutions are concentrated with a stream of nitrogen until they burst into a spray (Coulomb explosion) due to the electrostatic repulsion of the cations.

In our routine operation, we use a nitrogen flow of 200 °C at 0.3 bar and a consumption of 3.0 L/min

Sample delivery information:

1. sample delivery: approximately 1 mg of pure solid or liquid in a snap cap vial.

2. please fill in the order slip, giving the following information: a) Routine measurement via direct inlet with syringe pump.

b) Provide exact details (structure, formula) of the suspected product with exact mass information (Exact Mass).

c) Specify desired solvent for the spray.

The samples will be diluted by the measuring staff !!!

d) Routinely we measure with 5 eV Collision Cell energy.

We have as an additional option an APCI source, with which one has the possibility to determine molecules in an even more non-polar range as with the normal ESI source.

Order slips for the ESIMS measurements are available here.