Although mass spectrometry is a century-old technique, only since the 1980s it has emerged as a tool for biomolecular analysis, first and particularly in the field of Proteomics, lately also in the field of Genomics. Mass spectrometry has suddenly expanded out of research and assay laboratories into biology, medicine and therapeutics. ElectroSpray Ionization (ESI) and Matrix-Assisted Laser Desorption/Ionization (MALDI, Figure 1) yield increased mass-range and sensitivity, leading to novel applications and sparking new analyzer designs, software, and robotics.

Mass spectrometers equipped with Time of Flight (ToF) analyzers, separate ions according to their mass-to-charge ratio. Ions emitted from a source are accelerated towards a detector and the time each molecule takes to reach the detector is determined according to its mass-to-charge ratio (m/z). Therefore, molecules of smaller masses are accelerated at a given voltage 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.

When paired with so-called hard ionization sources that break molecules into fragments during ionization, ToF analyzers have limited use in protein, peptide, and nucleic acid analysis. But, when coupled with “soft” ionization methods -- MALDI and ESI -- ToF systems can be used to analyze even large biomolecules.

MALDI-ToF

In MALDI-ToF measurements, the analyte (biomolecule) is embedded in a matrix that consists of crystallized molecules. A laser (mostly UV-laser) is pointed to the matrix, which absorbs the laser energy and is volatilized, thus entraining the enclosed biomolecules in the gasphase. Here, the analytes are ionized and subsequently accelerated to a detector, which determines the biomolecule mass according to its time of flight (ToF measurement).

ToF measurement is initiated as soon as the laser is fired at the matrix. The time each molecule takes to reach the detector is determined according to its mass-to-charge ratio (m/z).

Due to the soft ionization of MALDI, mainly single charged molecules are formed and biomolecules are vaporized and ionized without being destructed. The resolution is improved by so-called delayed ion extraction, where the ionized molecules are not accelerated to the detector immediately after their formation, but delayed (usually around 150 ns) to reduce their temporal spread once they enter the ToF analyser. The principle processes in MALDI-ToF analysis are further schematically shown in the figure below.

Figure 1. Ionization and desorption processes in matrix-assisted laser desorption/ionization (MALDI, 1).

References

1. Pomastowski P., Buszewski B. Complementarity of Matrix- and Nanostructure-Assisted Laser Desorption/Ionization Approaches. Nanomaterials (Basel). 2019 Feb 14;9(2):260.
2. Barker J., Ando D.J., Davis R., Frearson M., and ACOL. Mass spectrometry: Analytical Chemistry by Open Learning. Second edition. Chichester: Wiley J. & Sons, 1999.
3. Crain PF., McCloskey JA.Applications of mass spectrometry to the characterization of oligonucleotides and nucleic acids. Curr Opin Biotechnol. 1998 Feb;9(1):25-34.
4. Hillenkamp F., Karas M., Beavis RC., Chait BT. Matrix-assisted laser desorption/ionization mass spectrometry of biopolymers. Anal Chem. 1991 Dec 15;63(24):1193A-1203A.  
   
   
   

MALDI-ToF Service Measurements - Portfolio

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 lyophilized (dry) or dissolved in water - metabion will supply you with the respective spectrum.

Please provide us with the following information:

• amount and concentration of the sample?
• expected molecular weight?
• which kind of molecules are contained in the sample (oligos…)?
• is the sample pure or a mixture of molecules?
• how is the sample produced? Chemically or enzymatically?
• is it purified? (Ions might disturb measurement)
• is it dissolved in water/buffer or organic solvent?

If you have a sample series or want us to measure your probes regularly please inquire for a quotation.

ESI-ToF

Although MALDI-ToF mass spectrometers are common in most analytical molecular biology facilities, MALDI has some limitations. Most notably, MALDI is a solid-state, pulsed technique that cannot easily be coupled online with liquid-based, continuous purification methods such as HPLC. For HPLC-based applications, ESI mass spectrometers are generally the tools of choice.

In ESI, a liquid sample is forced through a capillary tip in the presence of an electric field. As the liquid becomes charged, its molecules begin to repel each other, forming a fine mist of charged droplets. Solvent is evaporated using a neutral carrier gas, concentrating the charged analyte molecules into smaller droplets that then explode, due to repulsive forces between like charges. The process continues until analyte ions are completely stripped of solvent and only multiply-charged ions remain. The resulting spectrum is comprised of peaks representing different charge states of the analyte.

Scientists, cite ESI’s ability to generate multiply-charged ions as a major advantage, as this reduces the mass-to-charge (m/z) ratio of large ions, effectively extending the mass range of the spectrometer.

ESI-ToF Service Measurements - Portfolio

If you have no possibility to measure long or complex oligonucleotides by ESI-ToF in-house, we offer our profound experience in oligonucleotide mass spectrometry to help you elucidating your compound masses. You have the opportunity to choose ESI-ToF measurement without (w/o HPLC) or with (w HPLC) HPLC, which can be very useful to interpret complex oligonucleotide mixtures.

Do not hesitate to send us an aliquot of your sample, either lyophilized (dry) or dissolved in water - metabion will supply you with the respective spectrum (for ESI-ToF measurement with HPLC you will also receive an analytical HPLC chromatogram of your sample).

Please provide us with the following information:

• amount and concentration of the sample?
• expected molecular weight?
• which kind of molecules are contained in the sample (oligos…)?
• is the sample pure or a mixture of molecules?
• how is the sample produced? Chemically or enzymatically?
• is it purified? (Ions might disturb measurement)
• is it dissolved in water/buffer or organic solvent?

HOW TO ORDER

Send your inquiry by e-mail to info@mymetabion.com. If possible, indicate approximate amount, concentration and expected mass range of your sample.

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