ESI measurements

Q-TOF (ESIMS) measurements

In electrospray ionization mass spectrometry (ESIMS), samples are evaporated from a solution at atmospheric pressure and ionized before they enter 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 that are soluble in water, alcohols or acetonitrile. Uncharged sample substances are either protonated by these solvents or they form cationic adducts with sodium ions or, more rarely, with potassium or lithium ions.

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

Cationic compounds (e.g. pyridinium salts) can naturally 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, less frequently as protonated species, i.e. with a mass one higher. To calculate the molecular weights to be detected, the reduced masses ("exact mass" on the order form) are to be used, not those found in the periodic table of 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 due to the electrostatic repulsion of the cations (Coulomb explosion).

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

Information on sample delivery:

1. sample delivery: approx. 1 mg of pure solid substance or liquid in a snap lid vial.

2. please fill out the order form and provide the following information:
a) Routine measurement via direct inlet with syringe pump.

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

c) Specify the desired solvent for the spray.

The samples are diluted by the measuring personnel!

d) We routinely measure with 5 eV collision cell energy

As an additional option, we have an APCI source, with which it is possible to determine molecules in an even less polar range than with the normal ESI source.

Order forms for the ESIMS measurements are available here.