University:
Swansea University
Course:
PM134 | Microbiology
Academic year:

2023
Views:

195

Pages:

2
Author:

Amal J.

Mass Spectrometry Purpose: Used for quantitative analysis. Provides molecular weight accuracy up to ±0.01%. Used in molecular fragmentation and structural analysis of small molecules. Sample Processing: Molecules are ionized into gaseous ions. The ions are separated based on their mass-to-charge ratio (m/z). Analysis Process: Abundance Peak: The most intense peak is set to 100. Mass-to-Charge Ratio (m/z): Determines the mass spectrum, producing different peaks for species with multiple charges. Ionization Source: Electron Spray Ionization (ESI): Commonly used. Involves the ionization of molecules to form 𝑀 + M + , followed by fragmentation to form 𝑀 + , 𝑀 + + , 𝑀 + + − M + ,M ++ ,M ++− . Soft Ionization Technique: Used to prevent extensive fragmentation. Analyzer: Acts as a sieve, allowing smaller molecules to pass through first. Additional Notes on Mass Spectrometry Types of Analysis: MS/MS/MS: Tandem mass spectrometry, used for more detailed analysis. TOF (Time of Flight): Measures the time ions take to reach the detector, used to calculate molecular weight. Charge Difference in ESI: The charge difference is often by 1 unit. Formula: Mass-to-charge ratio 𝑚 𝑧 z m : 𝑚 𝑧 = 𝑀 + 𝑛 2 × 𝑋 𝑛 2 z m = n 2 M+n 2 ×X 𝑀 M = molecular mass. 𝑛 2 n 2 = number of charges. 𝑋 X = mass added. Protein Calculation: Average value is calculated using multiple m/z values. Amino Acids in Tandem MS: Specific amino acids like aspartate and glutamate are analyzed. Post-translation and Peptide Modification: Modifications can be studied using tandem MS.