Isotope Mass Calculation
Isotope Mass Calculation - Related Videos
01:13
Mass Spectrometry: Isotope Effect
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2025
Most elements exist in nature as a mixture of isotopes. The isotopes differ in weight due to their respective number of neutrons. The molecular weight of a molecule is different depending on the specific isotope of its elements involved. As a result, the mass spectrum of the molecule exhibits peaks from the same fragment at multiple positions. The positions of these mass signals depend on the mass differences between isotopes. Furthermore, the intensity of these signals is dependent on the...
12:07
Profiling Thiol Redox Proteome Using Isotope Tagging Mass Spectrometry
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Cited by 50 •
2012
Reactive oxygen species level is elevated when cells encounter stress conditions. Here we show the example of 3'-3' diaminobenzidine staining as well as cysTMT labeling and mass spectrometry to profile the redox proteome in Pseudomonas syringae treated tomato leaves.
09:26
Cellular Lipid Extraction for Targeted Stable Isotope Dilution Liquid Chromatography-Mass Spectrometry Analysis
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Cited by 6 •
2011
This protocol will demonstrate the extraction and analysis of free and esterified bioactive fatty acids from cells. Fatty acids are accurately quantified using stable isotope dilution, chiral liquid chromatography, electron capture atmospheric chemical ionization multiple reaction monitoring mass spectrometry (SID-LC-ECAPCI-MRM/MS).
02:31
Elements: Chemical Symbols and Isotopes
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2020
A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is used to indicate one atom of mercury (microscopic domain) or to label a container of many atoms of the element mercury (macroscopic domain). Some symbols are derived from the common English name of the element; others are abbreviations of the name in another language — Latin, Greek or German. For example, the symbol for aluminum (common name)...
01:52
Atomic Mass
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2020
Atoms — and the protons, neutrons, and electrons that compose them — are extremely small. For example, a carbon atom weighs less than 2 × 10−23 g. When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu). The amu was originally defined based on hydrogen, the lightest element, then later in terms of oxygen. Since 1961, it has been defined with regard to the most abundant isotope of carbon, atoms of which are...
FAQs
The key operation is a weighted average: each isotope mass is multiplied by its fractional abundance, and the products are added. An isotope that occurs more frequently therefore contributes more strongly to the calculated elemental mass than a rare isotope. This approach gives an abundance-based value rather than treating all isotopes as equally important.
A natural-isotope calculation combines the isotopes already present according to their abundances. An isotope-labeling calculation instead focuses on an experimentally introduced substitution and determines how that replacement changes the mass of a molecule. The first describes an abundance-weighted mass, whereas the second tracks a deliberate mass shift associated with labeling.
The calculation compares the molecule before and after one or more isotope substitutions. The mass contribution of the original isotope is removed, and the contribution of the introduced isotope is added for each affected position. The resulting difference represents the molecular mass change, which can be followed in experiments examining biomolecular synthesis or pathway activity.
List the relevant isotopes, record each isotope’s mass and fractional abundance, multiply each mass by its corresponding fraction, and sum the products. For a labeled molecule, identify the substituted positions and adjust the molecular mass for each replacement. Keeping natural-abundance and experimentally introduced isotopes separate helps clarify which part of the result reflects labeling.
Mass spectrometry measures molecular mass, so isotope calculations provide the expected mass values needed to interpret those measurements. Calculated shifts can indicate whether an experimentally introduced isotope is present in a molecule. In biological samples, this connection helps relate measured molecular masses to nutrient use, biomolecular synthesis, and activity within metabolic pathways.
They are useful when researchers need to follow how an introduced isotope is incorporated into biological molecules. By calculating the mass change caused by labeling and comparing it with measured molecular masses, investigators can examine nutrient use and biomolecular synthesis. These results also help reveal whether particular metabolic pathways are active in cells.