Invented about one decade ago, MALDI-ToF mass spectrometry revolutionized the mass analysis especially of large biomolecules like proteins, oligonucleotides and DNA/RNA fragments, respectively.
Until then, the mass of larger biomolecules (>1000-2000 Da) could only be approximately determined using mainly gel electrophoresis or gel permeation chromatography. However, exact masses are characteristic parameters for each molecule, essential for the structural elucidation of target compounds. The soft ionisation technique (MALDI) now allows the analysis of intact molecules of high masses.
The analyte (biomolecule) is embedded in a crystal of matrix molecules absorbing at the laser wavelength of the instrument (mostly UV-laser; Figure I). By the energy absorption the matrix is volatilised entraining the enclosed biomolecules in the gasphase, where they became ionised. In an electric field the ions are subsequently accelerated to the detector, which determines the masses according to the time of flight (ToF; Figure II).
Hereby, a fraction of the laser pulse initiates the timing for measuring the time of flight for the produced ions. According to the equation below (Figure II) molecules of smaller masses are accelerated at a given voltage (typically U=20kV) to higher velocities and hence reach the detector earlier compared to those with higher masses. By calibration of the instrument with molecules of known masses, the flight time of every analyte can be converted to the according mass, exactly speaking to m/z (m = mass; z = charge of the molecule).
Due to the soft ionisation of MALDI, mainly single charged molecules are formed, allowing determination of the molecular mass. The resolution is improved by so-called delayed ion extraction, a delay of the laser pulse and the application of the ion extraction field, allowing a correction for the initial kinetic energy distribution of the ions formed. The principle processes in MALDI-ToF analysis are further demonstrated schematically in the figures below.
For further information see also our literature references or just contact us.
Figure I: Principle of ionisation and volatilisation (M = matrix; A = analyte)
Figure II: Schematical illustration of the principle of MALDI-ToF mass spectrometry
References:
Baker J., Mass Spectrometry, ed. Ando D. J. (1999), John Wiley & Sons, Chichester, UK
Crain P. F. and McCloskey J. A. (1998) Application of mass spectrometry to the characterization of oligonucleotides and nucleic acids, Current Opinion in Biotechnology, 9, 25-34
Hillenkamp F. and Karas M. (1991) Matrix-Assisted Laser Desorption/ionization Mass Spectrometry of Biopolymers, Analytical Chemistry, 63, 1193A-1202A
What we offer
MALDI-ToF Service Measurements
If you have no MALDI-ToF mass spectrometer available to measure your own oligonucleotide samples, we offer you our profound experience in oligonucleotide mass spectrometry to help you in elucidating your compound masses. Do not hesitate to send us an aliquot of your sample either lyophilised (dry) or dissolved in water - metabion will supply you with the respective spectrum.
Indication of the approximate amount and concentration, respectively of your sample and of the expected mass range would be helpful.
Prices
| MALDI-ToF measurement | |
|---|---|
| Price € | |
| one sample incl. spectral data | 35.00 |
If you have a sample series or want us to measure your probes regularly please inquire for a quotation.