Mass Spectroscopy

MASS SPECTROSCOPYMVS RAO

According to IUPAC , it is the branch of science which deals with all the aspects of mass spectroscopes and results obtained

with these instruments

• it is one of the primary spectroscopic

methods for molecular analysis available to

an organic chemist

• It is a Micro analytical technique, requires

only a few nano moles of the sample to

obtain characteristic information about the

structure and the molecular weight

• It is not concerned with non destructive

interaction between molecules and the

electro magnetic radiation

• It involves in production and separation of

the ionized molecules and their ionic

decomposition product and measurement of

the relative abundance of different ions

produced resulting in consumption of the

sample during the analysis(destructive

technique)

• It is the most accurate method for

determining the molecular mass of the

compound and its elemental composition

• In this technique molecules are bombarded

with a beam of electrons

•Molecules are ionized and broken into many

fragments, some of which are positive ions

•Each kind of ion has a particular mass to

charge ratio(m/e ration), for most of the

ions the charge is one, therefore it is simply

the molecular mass of the ion.

BASIC PRINCIPLE

•A mass spectrum is the plot of relative

abundance of ions against their

mass/charge ration.

•The basic aspect of organic mass

spectroscopy consist of bombarding the

vapor of organic compound with a beam of

electrons accelerated from a filament to an

energy of 70ev to form positively charged

ions

•The additional energy of the electrons is

dissipated in breaking the bonds in the

molecular ion, which undergoes

fragmentation to yield several neutral or

positively charged species.

•This fragmentation may result in an even

electron ion and radical.

•The various positive ions, thus formed can

be accelerated and deflected by magnetic or

electric fields

USES

•Mass spectra is used in two general ways.

1. To prove the identity of two compounds.

2. To establish the structure of a new

compound.

• It deals with the examination of the

characteristics fragments(ions) arising from

the breakdown of organic molecules.

• It helps to establish the structure of a new

compound in several ways

1. It can give the exact molecular mass.

2. It can give a molecular formula or it can

reveal the presence of certain structural

units in a molecule.

APPLICATIONS

• It has both quantitative and qualitative uses.

•Helps in identification of unknown

compounds.

•Determining the isotopic composition of

elements in a molecule.

•Quantifying the amount of compound in the

sample.

•Determining the structure of a compound by

observing its fragmentation.

•Mass spectroscopy is now in very common

use in analytical laboratories that study

physical, chemical or biological properties

of a great variety of compounds.

Other uses

•Trace gas analysis, respired gas monitors

•Determining the isotopic compounds of

elements within a sample

•Pharmacokinetics, protein characterization

•Glycan analysis and space exploration.

SUMMARY OF MS• METHOD: Mass spectroscopy

• PRINCIPLE: When a substance in gaseous/vapor state is

bombarded with a beam of electrons the molecules get

ionized or breakdown into fragments. These fragments

are sorted and recorded based on their

masses/molecular weight. The data is then compiled to

deduce the molecular weight of the sample analyzed.

• LIMITATIONS: It is difficult to analyze non-volatile

samples.

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