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Mass Spectrometry: Alkyl Halide Fragmentation01:22

Mass Spectrometry: Alkyl Halide Fragmentation

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Chlorine isotopes exist as 35Cl and 37Cl in a 3:1 ratio, while bromine isotopes exist as 79Br and 81Br in a 1:1 ratio. The mass spectrum of alkyl halides typically produces two distinct molecular ion peaks, the molecular ion peak, [M], and the molecular ion plus two, [M + 2] peak. The relative heights of these two peaks are proportional to the isotopic abundance ratios of the halide. For example, 2‐chloropropane and 1‐bromopropane display two peaks with relative peak heights in a 3:1 and...
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In gravimetry, the precipitant is chosen carefully to obtain a pure solid that can be easily filtered. Common inorganic precipitants can be used to determine several cations and anions. In some cases, the formation of the same precipitate can be used to determine the cation and the anion. For example, the reaction of barium and chromate ions to give barium chromate is used to determine both barium and chromate. However, precipitates such as hydroxides, oxalates, and metal ammonium phosphates...
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Carboxylic acids react with SOCl2 or PCl5 to form acid chlorides. Amongst the carboxylic acid derivatives, acid chlorides are the most reactive and synthetically important derivatives. They are useful reagents for Friedel–Crafts acylation of some aromatic compounds.
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The pH of a solution containing an acid can be determined using its acid dissociation constant and its initial concentration. If a solution contains two different acids, then its pH can be determined using one of several methods depending upon the relative strength of the acids and their dissociation constants.
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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...
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Perchlorate in stratospheric aerosol particles.

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Proceedings of the National Academy of Sciences of the United States of America
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The stratosphere is a significant source of atmospheric perchlorate, a toxic drinking water contaminant. Its presence in specific aerosol particles suggests potential increases with climate interventions.

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Area of Science:

  • Environmental Chemistry
  • Atmospheric Science
  • Geochemistry

Background:

  • Perchlorate is a regulated contaminant found in drinking water.
  • Previous isotopic studies suggest atmospheric formation and stratospheric contribution to deposited perchlorate.
  • The exact atmospheric sources and formation pathways remain incompletely understood.

Purpose of the Study:

  • To measure perchlorate concentrations in stratospheric aerosol particles.
  • To identify the atmospheric layers responsible for perchlorate production.
  • To investigate the types of particles associated with stratospheric perchlorate.

Main Methods:

  • Analysis of perchlorate in stratospheric aerosol samples.
  • Measurement of mass mixing ratios (pptm).
  • Correlation of perchlorate presence with specific aerosol particle types (biomass burning, nitrogen-rich).

Main Results:

  • Perchlorate was detected in stratospheric aerosol particles, confirming the stratosphere as a key source.
  • No perchlorate production was observed in the troposphere.
  • Stratospheric perchlorate concentrations ranged from 1 to 10 parts per trillion by mass (pptm), peaking in summer and the Southern Hemisphere.
  • Perchlorate predominantly resides in biomass burning and nitrogen-rich particles, not sulfuric acid particles.

Conclusions:

  • The stratosphere is a significant source of atmospheric perchlorate.
  • Perchlorate formation may be linked to particle acidity, with less acidic particles hosting higher concentrations.
  • Potential for increased global perchlorate production if solar radiation modification strategies involve injecting materials into the stratosphere.