What are the operating steps of MALDI-TOF MS?
The key operational steps of MALDI-TOF MS typically include: sample preparation, sample introduction into the instrument, laser desorption/ionization, ion acceleration and flight, mass spectrometry detection, and data analysis.
1. Sample Preparation
The sample to be tested, such as proteins or peptides, after purification or concentration, is mixed with a matrix (usually an organic acid, such as α-cyano-4-hydroxycinnamic acid) in a specific ratio. A micro pipette is then used to drop the mixture onto the MALDI target plate, allowing it to dry and form crystals.
2. Sample Introduction into the Instrument
The MALDI target plate with the sample is placed into the vacuum chamber of the mass spectrometer. A vacuum environment reduces molecular collisions and improves detection accuracy.
3. Laser Desorption/Ionization
A pulsed laser is used to irradiate the mixture of sample and matrix. The matrix absorbs the laser energy, rapidly heats up, and vaporizes, causing the sample molecules to desorb and ionize, forming charged ions.
4. Ion Acceleration and Flight
An electric field accelerates the generated charged ions into the flight tube. The charged ions travel through the flight tube at different speeds, depending on their mass-to-charge ratio (m/z).
5. Mass Spectrometry Detection
By detecting the time it takes for ions to reach the detector, the mass spectrometer can calculate the flight time of ions with different mass-to-charge ratios and generate the corresponding mass spectrum. The shorter the time to reach the detector, the smaller the mass-to-charge ratio of the ion.
6. Data Analysis
Mass spectrometry data is processed and analyzed using specialized software to generate a mass spectrum. By comparing the sample's mass spectrum with a known database, proteins can be identified and analyzed.
The core of the entire process is to use laser desorption/ionization technology to convert sample molecules into gaseous ions, and then use time-of-flight to detect the mass-to-charge ratios of these ions, thereby analyzing the sample's composition.
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