Why do chemical species in a mass spectrometer need to be positively charged to be detected?

Answer 1

Technically they don't. Some MS can detect negatively charged ions.

But commerical MS and even most research MS use positive ions b/c you can take an electron off of any species to make a positive ion. You can't always add an electron and get it to stick.

Once the electron is removed the "optics" that focus the ions, whether magnets, quadrupoles or defelctor plates (TOF-MS) are all designed to direct positive ions toward the detector. Neutral species won't deflect; and negatively charged species not hit the detector.

Answer 2

The mass spectrometer will bombard the pattern with extreme capability electrons to supply the two certainly and negatively charged ions of the unique textile and fragments of it. whether to then enable them to be sped up out of the ionisation chamber into the detection chamber they might desire to hold an outstanding can charge to be repelled out of the ionisation chamber into the detector. The certainly charged ions will then be deflected via a magnetic container on a similar time as traveling during the spectrometer; the quantity of the deflection would be proportional to the mass of the fragment or unique textile. adverse ions is merely no longer sped up in the direction of the detector. The mass spec will furnish a signature for the substance, that can then be interpreted to infer the commencing textile from the mass to can charge ratio of the fragments and the commencing textile. adverse ions may be detected if a opposite magnetic container is used, yet it relatively is uncommon as ionisation products are predominantly constructive ions.

Answer 3

If the species are not charged, they won't be deflected by the magnets. If they're not deflected by the magnets, they won't hit the detector.

Answer 4

B/c the device uses negative charges to read the chemicals, if they were both positive, they would repel.