Q.9The technique that involves impacting samples with electrons is _______.
Electron Impact (EI) ionization in mass spectrometry is the technique that involves impacting samples with electrons, though it’s not listed among the options; however, among the given choices, none precisely match, with ESI being a common confusion point in such questions.
Option Analysis
NMR Spectroscopy uses radiofrequency pulses in a magnetic field to probe nuclear spins, not electrons impacting samples. No electron bombardment occurs.
ESI Mass Spectrometry employs electrospray to form charged droplets from liquid samples, evaporating solvent to release ions without direct electron impact. It’s a soft ionization method avoiding harsh fragmentation.
IR Spectroscopy measures infrared light absorption for molecular vibrations and functional groups. Electrons play no direct role in sample interaction.
UV-Vis Spectroscopy detects electronic transitions via ultraviolet-visible light absorption. Samples interact with photons, not free electrons.
Correct Technique
The described process matches Electron Impact (EI) Mass Spectrometry, where vaporized samples are bombarded by a 70 eV electron beam, producing molecular ions and fragments. This “hard” ionization causes significant fragmentation for structural analysis, commonly paired with GC-MS. Note: Questions like this often test EI knowledge, mislabeled under mass spectrometry options.
The impacting samples with electrons technique revolutionizes mass spectrometry by directly bombarding vaporized molecules with high-energy electrons, enabling precise molecular weight and fragmentation analysis essential for CSIR NET Life Sciences.
Ionization Principles
In Electron Impact (EI) ionization, samples vaporize in a vacuum chamber where a heated filament emits electrons accelerated at 70 eV to strike gas-phase molecules, ejecting an electron to form radical cations (M+- ). This leads to abundant fragments for spectral libraries.
-
Produces molecular ion peak for exact mass.
-
High fragmentation aids structural elucidation.
-
Ideal for volatile, stable compounds in GC-MS.
Comparison Table
| Technique | Ionization Method | Sample Interaction | Key Application |
|---|---|---|---|
| EI Mass Spectrometry | Electron bombardment (70 eV) | Direct impact with electrons | Structural analysis |
| ESI Mass Spectrometry | Electrospray droplet evaporation | No electron impact; soft ions | Biomolecules |
| NMR Spectroscopy | RF pulses in magnetic field | Nuclear spin excitation | Molecular structure |
| IR Spectroscopy | IR photon absorption | Vibrational transitions | Functional groups |
| UV-Vis Spectroscopy | UV-Vis photon absorption | Electronic transitions | Concentration |
CSIR NET Relevance
For competitive exams like CSIR NET, distinguishing EI’s electron impact from ESI’s gentle electrospray is crucial, as EI suits small organics while ESI handles proteins without fragmentation. Mastery aids biotechnology and analytical sections.
