Mass Spectrometry
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What is Mass Spectrometry?
Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio (m/z) of ions within a sample. In peptide research, mass spectrometry is used alongside HPLC to confirm the molecular identity of synthesized peptides. The process involves three fundamental steps: ionization of the sample molecules, separation of the resulting ions based on their mass-to-charge ratios, and detection of those ions to produce a mass spectrum. The spectrum serves as a molecular fingerprint, enabling researchers to confirm that the synthesized peptide matches the intended sequence and molecular weight.
Common MS Techniques in Peptide Analysis
Several ionization methods are commonly used for peptide analysis. Electrospray ionization (ESI) is widely employed because it can handle a broad range of peptide sizes and is easily coupled with HPLC systems (LC-MS). Matrix-assisted laser desorption/ionization (MALDI) is another popular technique, particularly useful for analyzing larger peptides and proteins. In MALDI, the sample is embedded in a crystalline matrix and ionized by a laser pulse. Both methods produce multiply charged ions that can be analyzed by time-of-flight (TOF), quadrupole, or ion trap mass analyzers.
Interpreting Mass Spectrometry Data
The primary output of a mass spectrometry analysis is the mass spectrum, a plot of ion signal intensity versus mass-to-charge ratio. For peptide quality control, the observed molecular weight is compared against the theoretical molecular weight calculated from the peptide's amino acid sequence. A match within acceptable tolerance (typically less than 0.1% deviation) confirms the peptide's identity. Mass spectrometry can also reveal the presence of modifications, truncations, or impurities that might not be apparent from HPLC analysis alone, making it an indispensable complementary technique.
MS and Quality Assurance
At Pure U.S. Peptides, mass spectrometry data is included in every Certificate of Analysis alongside HPLC results. Together, these two analytical methods provide a comprehensive quality profile: HPLC confirms purity, while MS confirms identity. This dual-verification approach ensures that researchers receive exactly the peptide they ordered, at the purity level they require for rigorous, reproducible experimentation.