Abstraction of a proton (H+) from the analyte.

Means that you can observe compound with negative charge only. The negative charge is obtained by the loss of a proton H+, so called deprotonation.

Therefore, in negative mode

Value = mass / charge = (Natural mass – z x 1.007276) / z

with Z = to the number of H+ your compound have lost during ionization.

Example: methanol. Formula CH3OH, mass = 32.026, value in negative mode = 31.019 corresponding to CH3O-

How can I do that?

Yvl,

ESI-MS negative ion mode (when the spraying nozzle is kept at negative potential) charging occurs via deprotonation of the analyte.

To gain more knowledge on the ESI mass spectrometry technique and the deprotonation please go to

---http://www.hindawi.com/journals/ijac/2012/282574/

On how to run the experiment, you may consult your instrument manual.

Good luck

This involves removal Hydrogen ion from the compound. One or more proton can be removed. That depends on the ease of removal of such protons. Therefore, you may not actually observe molecular ion in the spectrum, but a peak which 1 unit less as the molecular ion. i.e [M-H]

Deprotonation is the removal of a hydrogen ion (H+) from a molecule. Analytes for ESI-MS analysis must either exist as preformed ions in solution or charged by protonation, deprotonation, adduct formation, electrochemical oxidation or reduction. ESI process generates vapour phase ions that can be analyzed for mass-to-charge ratio within the mass spectrometer. Charge separation is the primary method by which ions are formed for organic and biological molecules with acidic or basic functional groups. Proteins, with their multiple basic amino acid residues, readily form positively charged ions through protonation, whereas oligonucleotides and fatty acids can be negatively charged through deprotonation of acidic groups. Positively charged ions such as protonated organic bases are analyzed in the positive ion mode, whereas negatively charged ions such as inorganic anions and deprotonated organic acids are analyzed in the negative ion mode. Upon collisional activation, the deprotonated molecular ions [M – H]− dissociate in two reaction channels, both of which involve intramolecular rearrangement. In the case of basic analytes like amines, the protonated pseudo molecular ions ([M+H]+) are used as precursors ions for following collision experiments and spectra acquisitions. Organic acids or other acid compounds are negatively charged ([M-H]) via deprotonation and the deprotonated pseudo molecular ions are selected as precursor ions. For further details, you may refer attached paper