How to Determine Molecular Weight?
What Is Molecular Weight?
Molecular weight (MW), also referred to as relative molecular mass, is defined as the ratio of the mass of a molecule to one-twelfth of the mass of a carbon-12 atom, with units of Dalton (Da) or g/mol. In practical applications, particular attention is often given to the exact molecular mass, which is calculated based on the precise isotopic masses of constituent atoms and is especially critical in mass spectrometric analysis.
Summary of Common Methods for Determining Molecular Weight
Determination of Molecular Weight by Mass Spectrometry
1. Principle of Mass Spectrometry
Mass spectrometry (MS) ionizes molecules into ions and separates and detects them according to their mass-to-charge ratio (m/z) as they migrate through an electric or magnetic field.
2. Commonly Used Platforms
(1) ESI-MS (Electrospray Ionization): suitable for proteins, peptides, metabolites, and related biomolecules.
(2) MALDI-TOF-MS (Matrix-Assisted Laser Desorption/Ionization Time-of-Flight): widely used for proteins and polymers.
(3) HRMS (High-Resolution Mass Spectrometry, e.g., Orbitrap, Q-TOF): enables the determination of exact molecular masses for molecular formula elucidation.
Determination of Protein Molecular Weight by SDS-PAGE (Applicable for Routine Laboratory Verification)
SDS-PAGE is based on the principle that proteins migrate according to their molecular size in an electric field, with molecular weights estimated relative to standard protein molecular weight markers.
1. Advantages
Simple operation and low cost. Allows rapid estimation of protein purity and size.
2. Limitations
Limited resolution, particularly for proteins of similar size. Post-translational modifications such as glycosylation and polymerization can alter migration behavior.
Selection of an Appropriate Method for Determining Molecular Weight
MtoZ Biolabs is equipped with advanced mass spectrometry platforms, including Orbitrap Exploris, TripleTOF, and QqQ systems, which are capable of performing professional molecular weight determinations for a wide range of molecular types:
(1) Comprehensive molecular weight analysis for proteins, peptides, and metabolites.
(2) Accurate molecular formula prediction and structural annotation.
(3) Customizable LC-MS workflows integrating both quantitative and qualitative analyses.
(4) Provision of complete spectral data, raw files, and analytical reports suitable for scientific publication.
Whether in basic chemical synthesis, protein expression validation, or quality control during new drug discovery, accurate molecular weight determination is an essential step. The selection of an appropriate method ensures a robust foundation for subsequent research.
MtoZ Biolabs, an integrated chromatography and mass spectrometry (MS) services provider.
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