How to Read a Simple Mass Spectrum

There are three key stages to the spectrometer:

• Ionization. Molecules in a sample are vaporized (converted to the gas phase by heating).
• Acceleration and Deflection. Next, the ions are sorted according to mass in two stages – acceleration and deflection.
• Detection.

The relative abundance for a specific ion in the sample can be calculated by dividing by the number of ions with a particular m / z m/z m/z ratio by the total number of ions detected. At the end of the experiment, the instrument generates a mass spectrum for the sample, which plots relative abundance vs. m/z .

1. Introduction: How to Read a Simple Mass Spectrum.
2. Step 1: Step 1: Identify the Molecular Ion.
3. Step 2: Step 2: Identify Major Fragmentation Clusters.
4. Step 3: Step 3: Determine the ∆m for Each Major Peak.
5. Step 4: Step 4: Identify Any Heteroatoms.
6. Step 5: Step 5: Identify Remainder of Molecule.
7. Step 6: Step 6: Name the Molecule.

Ions are created in the ion source. If a high vacuum provides a long mean free path exceeding the dimension of the chamber, ions can easily reach the detector. QPMS is usually operated at around 10-3 to 10-4 Pa pressure, which corresponds to 5m to 50m of a mean free path.

Reflectron TOF The reflectron uses a constant electrostatic field to reflect the ion beam toward the detector. A point of simultaneous arrival of ions of the same mass-to-charge ratio but with different energies is often referred as time-of-flight focus.

TOF mass spectrometers have several advantages, including (1) a nearly unlimited m/z range, (2) high acquisition speed, (3) high mass accuracy, (4) moderate to high resolution, (5) moderate to high sensitivity, (6) absence of spectral distortions when used in conjunction with fast separations and narrow chromatographic …

Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) provides elemental, chemical state, and molecular information from surfaces of solid materials. The average depth of analysis for a TOF-SIMS measurement is approximately 1 nm.

In the case of MALDI-TOF, the analyzer separates molecules based on the time it takes each of them to fly through the time-of-flight tube or “drift” region to the detector. The ionized sample molecules are accelerated by a high-voltage current and fly through the tube before striking the detector.

Using standardized procedures, the resolution of MALDI-TOF MS allows accurate identification at the species level of most Gram-positive and Gram-negative bacterial strains with the exception of a few difficult strains that require more attention and further development of the method.

MALDI-TOF (matrix-assisted laser desorption/ionization time-of-flight) mass spectrometry is a new technology that has revolutionized pathogen identification and has also proven to accelerate detection of antimicrobial resistance compared to the traditional antibiotic susceptibility tests (AST) as well as DNA …

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UNC Hospitals purchased the MALDI-TOF MS in 2012 for approximately $250,000 from bioMérieux due in part to the company’s location in north Durham and UNC Health Care’s previous collaborations with the company. “For a microbiology lab, that’s a lot of money,” Gilligan said.

Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has become a widely used technique for the rapid and accurate identification of bacteria, mycobacteria and certain fungal pathogens in the clinical microbiology laboratory.

MALDI-TOF measures the mass of molecules from a sample that has been embedded in a matrix by using a laser to ablate and desorb the molecules with minimal fragmentation. …

MALDI-TOF method successfully detects viruses in a wide variety of biological specimens, and the concordance rate between MALDI-TOF and these techniques is high. MALDI-TOF MS methods also allow large-scale research studies not only for fresh samples but also on archival samples from several biological specimens.

Matrix Assisted Laser Desorption/Ionization

Molecular techniques can generate results and positive identifications remarkably quickly; so can Matrix-Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF) mass spectrometry, which is having a significant impact on clinical microbiology. MALDI-TOF generates high throughput of dozens of pathogens per run.

A number of organic compounds have been used as matrices for MALDI-TOF MS but for microbiological applications, α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxy benzoic acid (DHB), and 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid) have been found to be the most useful.

Koichi Tanaka

Franz Hillenkamp

1980s

MALDI has become one of the most common ionization methods because it causes little to no fragmentation of the molecule during ionization and desorption. The matrix compound absorbs the light and uses the energy to eject and ionize the embedded protein molecules.

MALDI-TOF MS overview. MS is used to detect the m/z ratio and MALDI-TOF MS provides a rapid, accurate, and sensitive spectra of the bio-analytes within a sample. MALDI is an ionization technique in which a matrix absorbs energy from ultraviolet lasers to create ions from large molecules with minimal fragmentation.