Special relativity introduced a new framework for all of physics by proposing new concepts of space and time. Equivalence principle A person in a free-falling elevator experiences weightlessness ; objects either float motionless or drift at constant speed.
It is used for determining masses of particles, for determining the elemental composition of a sample or molecule. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios by using the one of a variety of techniques e.
Since EI samples are thermally desorbed to the gas phase and subjected to the high energy of EI, analytes must be thermally stable. The gas phase molecules enter into the An introduction to the analysis of mass source where they are bombarded with free electrons emitted from a filament Figure 1.
The electrons bombard the molecules causing a hard ionization that fragments the molecule, and turn into positively charged particles called ions.
This is important because the particles must be charged to pass through the analyzer. The filter continuously scans through the range of masses as the stream of ions come from the ion source.
A detector counts the number of ions with a specific mass.
This information is sent to a computer and a mass spectrum is created. The mass spectrum is a graph of the number of ions with different masses that traveled through the analyzer.
Schematic diagram of EI Source B Chemical Ionization CI technique CI technique is especially useful when no molecular ion is observed in EI mass spectrum of a compound, and also in the case of confirming the molecular weight of a compound.
CI technique uses nearly the same ion source device as in EI, except, CI uses tight ion source, and a reagent gas Figure 2. Schematic diagram of CI source Reagent gas is first subjected to electron impact to yield reagent gas ions.
These initial reagent gas ions further undergo ion-molecule reactions with neutral reagent molecules R to yield reagent selective ions reagent plasma, e. When sample is introduced, the sample molecules A undergo ion-molecule reactions with reagent plasma to produce sample ions.
In general, reagent gas molecules are present in the ratio of about Unlike in EI method, the CI process is soft ionization and yields abundant quasi-molecular ions, with less fragment ions. In CI mass spectrometry the molecules of a vaporized sample are ionized by a set of reagent ions reagent plasma in a series of ion-molecule reactions.
The energy transferred by these reactions is lower than the energy imparted by electrons in EI source, and therefore fragmentation of the sample molecules is greatly decreased.
For this reason CI mass spectrometry has been finding increasing use as a tool for the molecular weight confirmation and for elucidation of structure of variety of organic compounds including differentiation of isomeric compounds.
The spraying process can be streamlined by using a nebulizing gas. The charged droplets are produced in which the positive or negative ions are solvated with solvent molecules. Heat gas or a dry gas, usually called as desolvation gas is applied to the charged droplets to cause solvent evaporation.
The desolvation process decreases the droplet size, leads to the columbic repulsion between the charges present in the droplet and further the droplet fission leads to the formation of individual gas phase analyte ions that critical point known as the Rayleigh limitthat are guided through ion optics into the mass analyzer.
ESI can produce singly or multiply charged ions. The number of charges retained by a particular analyte depends on several factors such as the size, chemical composition, and higher order structure of the analyte molecule, the solvent composition, the presence of co-solutes, and the instrument parameters.
Schematic diagram of Electro spray ionization process ESI is very suitable for a wide range of biochemical compounds including peptides and proteins, lipids, oligosaccharides, oligonucleotide, bio-organic compounds, synthetic polymers, and intact non-covalent complexes.
D Atmospheric pressure chemical ionization APCI technique PCI has also become an important ionization source because it generates ions directly from solution and it is capable of analyzing relatively non-polar compounds.
These ions react with analyte molecules to form singly charged protonated or deprotonated analyte ions. In the negative ion mode, either electron transfer or proton loss occurs to yield M.
The moderating influence of the solvent clusters on the reagent ions, and of the high gas pressure, reduces fragmentation during ionization and results in primarily intact quasi-molecular ions.
Multiple charging is typically not observed presumably because the ionization process is more energetic than ESI. E Atmospheric solid Analysis probe ionization ASAP ASAP ionization is used for the direct analysis of volatile, semi volatile, solid and liquid samples at atmospheric pressure, it is also known as one of the atmospheric pressure ionization API technique.
The sample is placed on surface of glass capillary tube and the glass tube inserted into source just adjacent to discharge corona needle which is provided 2 to 4kV.It is commonly coupled to MS analysers such as the triple quadrupole (QqQ), which can be used in both qualitative and quantitative analysis, and the time-of-flight (TOF) instrument which can determine accurate mass to 4 decimal places.
References >> Mass Spectrometry. Mass Spectrometry. Mass spectrometry is a powerful analytical technique used to quantify known materials, to identify unknown compounds within a sample, and to elucidate the structure and chemical properties of different molecules.
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Media Overview and Planning/buying Page 1 AJEEP Media Overview numerical analysis, media research, and strategic media planning. We will also discuss and review current media situations in Media needs mass to remain viable – the more people that. Mass cytometry is a specific implementation of inductively coupled plasma mass spectrometry (ICP-MS, atomic mass spectrometry) that enables an unprecedented degree of multi-parametric single cell analysis and provides an opportunity for absolute quantification.
Introduction to Spectroscopy. In previous sections of this text the structural formulas of hundreds of organic compounds have been reported, often with very little supporting evidence.