MALDI-TOF
Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry · Also known as: MALDI mass spectrometry, MALDI-TOF-MS, laser desorption mass spectrometry
Matrix-Assisted Laser Desorption/Ionization (MALDI) combined with Time-of-Flight (TOF) mass analysis, or MALDI-TOF, is a soft ionization mass spectrometry technique that gently ionizes intact biomolecules and volatile organic compounds, then measures their mass-to-charge ratio by measuring flight time through a field-free drift region. Introduced independently by Karas, Hillenkamp, and Tanaka in 1988, MALDI-TOF revolutionized proteomics, microbiology, and organic analysis by enabling mass determination of proteins and polymers exceeding 100 kDa.
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When to use it
Apply MALDI-TOF to characterize proteins, peptides, polymers, and small organic molecules when you need rapid, sensitive mass determination without complex sample preparation. MALDI excels for complex mixtures and when fragmentation must be minimal. It is ideal for microbial identification. MALDI-TOF is robust, relatively inexpensive, and fast; typically 1 minute per sample from analysis start to mass spectrum. Assumes matrix selection is appropriate for the analyte and that ionization efficiency is adequate.
Strengths & limitations
- Gentle ionization preserves labile bonds; intact molecular ions dominate, making mass determination straightforward
- Extremely fast analysis; MALDI instruments can profile hundreds of samples per hour
- Low cost compared to FT-ICR or Orbitrap; MALDI-TOF instruments are affordable and widespread
- Tolerance for salt, buffers, and contamination; matrix often suppresses interference
- Lower mass resolution (< 10,000) compared to FT-ICR or high-resolution TOF; chemical formula determination is less precise
- Quantification is difficult because ionization efficiency varies with analyte properties and sample matrix composition
- Small molecules (< 500 Da) are challenging due to chemical noise from matrix peaks
- Spectral quality depends critically on matrix choice and crystal size; optimization is often needed
Frequently asked
Why is matrix selection critical in MALDI?
The matrix must absorb photons at the laser wavelength, transfer energy efficiently to analyte molecules, and facilitate ionization without reacting. Common matrices include alpha-cyano-4-hydroxycinnamic acid for peptides and proteins, 2,5-dihydroxybenzoic acid for oligonucleotides, and dithranol for lipids. Incorrect matrix leads to poor or absent ionization.
How is MALDI different from electrospray ionization (ESI)?
MALDI uses laser pulse ionization and works on solid samples; ESI uses ambient electrical ionization from solution. MALDI is faster and tolerates salts better; ESI is more compatible with liquid chromatography and achieves higher resolution on some instruments. Both are soft ionization methods suitable for biomolecules.
What does the [M+H]+ ion represent?
The [M+H]+ ion is the intact analyte molecule M with one additional proton. It is the most common positive ion in MALDI because the matrix efficiently donates protons. Mass is read directly from the m/z (mass-to-charge ratio) of this peak; dividing by the charge (1 in this case) yields the true molecular mass.
Sources
- Karas, M., & Hillenkamp, F. (1988). Laser desorption ionization of proteins with molecular masses exceeding 10,000 daltons. Analytical Chemistry, 60(20), 2299-2301. DOI: 10.1021/ac00171a028 ↗
- Tanaka, K., Waki, H., Ido, Y., Akita, S., Yoshida, Y., & Yoshida, T. (1988). Protein and polymer analyses up to m/z 100,000 by laser ionization time-of-flight mass spectrometry. Rapid Communications in Mass Spectrometry, 2(8), 151-153. DOI: 10.1002/rcm.1290020802 ↗
- Fenn, J. B., Mann, M., Meng, C. K., Wong, S. F., & Whitehouse, C. M. (1989). Electrospray ionization for mass spectrometry of large biomolecules. Science, 246(4926), 64-71. DOI: 10.1126/science.2675315 ↗
How to cite this page
ScholarGate. (2026, June 3). Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry. ScholarGate. https://scholargate.app/en/spectroscopy/maldi-tof
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
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