# DBT JRF 2020 — Question 69

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Easy

## Question

Which of the following methods first ionizes a protein before separation and detection?

## Options

- **A.** nuclear magnetic resonance
- **B.** reverse phase chromatography
- **C.** mass spectrometry
- **D.** fluorescence spectroscopy

## Answer

Option C

## Explanation

Mass spectrometry (MS) is the only method listed that requires IONISATION of the analyte before analysis. In protein MS: Electrospray Ionisation (ESI) — spray of protein solution through high-voltage needle creates multiply-charged ions ( $[M+nH]^{n+}$ ) at atmospheric pressure, ideal for coupling with LC (LC-MS/MS). Matrix-Assisted Laser Desorption/Ionisation (MALDI) — protein co-crystallised with UV-absorbing matrix, laser pulse causes desorption and ionisation. Ions are then separated by mass-to-charge ratio ( $m/z$ ) in the analyser (TOF, quadrupole, Orbitrap). NMR — exploits nuclear spin in magnetic fields (no ionisation). Reverse phase HPLC — separation by hydrophobicity (no ionisation). Fluorescence spectroscopy — excites fluorophores with light (no ionisation).

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