Transcript Basic Physics in Mass spectrometry - GK-12

» Objectives of the presentation
˃To get an appreciation of the role of
physics in our day to day living
˃Acquaint ourselves to a novel and
widely used research tool: Mass
Spectrometer
˃To introduce the basic physics of mass
spectrometry
˃Relate Physics activities in class to
processes in Mass Spectrometry
 Explosives and narcotic trace detection is
paramount
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Carry-ons scanned! Safe to fly?
Source: Southwest Airlines Co.
What is mass spectrometry?
“An art of measuring atoms
and molecules to determine
their molecular weight by
putting charge on the
molecules of interest and
then measure how the
trajectories of the resulting
ions respond in vacuum to
various combinations of
electric and magnetic
fields”- John B. Fenn. (The
Nobel Prize winner in
Chemistry 2002)
» Atom: Basic unit of a chemical element
» Molecule: Refers to two or more atoms which are
chemically combined.
» Mass- The quantity of matter in a body
» Trajectory- is the path that a moving object follows
through space as a function of time
Charge- An ion is an atom or molecule in which the
total number of electrons is not equal to the total
number of protons, giving the atom a net positive or
negative electrical charge.
In research and pharmaceutical
industries, molecules of interest
include proteins, sugars, DNA,
drugs, and many other biologically
relevant molecules
» Samples are specially prepared before analysis by Mass
Spectrometry
» They may include:
» Blood, Urine, Drugs etc.
» We use Kilograms and Grams in
Physics.
» These units are too large for small
samples
» Mass Spectrometry uses Daltons(Da)
» 1 Da= 1.66x10-24 grams ( Remember
how to write in scientific notation?)
 Examination of the
characteristics of
fragments(ions) arising
from breakdown of organic
molecules
 A mass spectrum is the plot
of relative abundance of
ions against their mass to
charge ratio
(http://www.youtube.com/
watch?v=tOGM2gOHKPc)
» 3 Basic Steps
˃Ion source
˃Mass analysis
˃Detection
Source: Select Science
» Rocket Launching! Recent Physics lesson
Why the shape?
 NB: Pointed front
 Angled wings
All this is to reduce
Frictional Drag: the
retarding force produced
by an object sliding past
the molecules of the fluid
through which it is
moving. NB: you can only
reduce but not eliminate
it
 Powerful pumps are
employed to pump out air
and ensure vacuum in the
mass spectrometer
 Ions need not collide
with air molecules
 Reducing frictional drag
just like in the rockets
» Various ionization methods applied in MS
˃ Sample mixture absorbs the ultraviolet light and converts it to heat
energy, the matrix and the sample heats rapidly and is turned into vapor
from which ions are extracted.
˃ An applied voltage on the plates forces the vaporized mixture out of the
plate into the analyzer
˃ Physics behind- Applied energy causes the solid mixture to expand, melt
and eventually vaporize( The vapor is made of ions which proceed to
mass analyzer)
˃ Remember Newton’s First Law: Objects at rest will remain at rest, and
objects in motion will stay in motion in a straight line unless acted upon
by an external unbalanced force.
 Mass analyzers separate the ions according to their mass-to-charge ratio
 Utilizes Newton’s second Law of Motion
 Here F is the force applied to the ion, m is the mass of the ion, a is the
acceleration(http://www.youtube.com/watch?v=NuIH9-6Fm6U)
 If two rockets A(75g)and B(150g) with all other similar
specifications were launched on a windy day, which one will
be recovered further away from the launch site?
 The same way ions are separated in Mass Spectrometry!
» Ions analyzed according to their speed
» What physics that is employed here?
˃ Vd = The ion’s drift velocity
𝑑𝑑
Vd =
˃ dd= Ion’s drift distance
𝑡𝑑
˃ td = Ion’s drift time
» An inert gas like Helium is used as the drift gas
» An important formula that helps analyze the ions is
𝑚1 𝑚2
𝝁 =
𝑚1 + 𝑚2
» Where
˃ μ= ion-neutral reduced mass
˃ M1= Mass of the ion
˃ M2=Mass of neutral gas atom
» This is an inelastic collision (kinetic energy is
converted into other forms of energy) Compare the
formula with inelastic collision momentum equation
More Physics!
» The ion hits the metal, its charge
is neutralized by an electron from
the metal on to the ion, leaving a
space amongst the electrons.
» Flow of electrons in the wire is
detected as an electric current
which can be amplified and
recorded
» The output from the recorder is
usually simplified into a "stick
diagram“ known as spectra
(singular spectrum)
» The Spectrum is indicates the
M/Z ratio-Mass Spectrometry
» The portal passes
puffs of air to
dislodge particles
from hair, clothes,
skin and shoes
» These particles are
heated and boiled
off into gaseous
phase for detection
by Mass
Spectrometer
Heavily employed for military or security purposes such as
detecting drugs and explosives
The capacity to learn is a gift;
The ability to learn is a skill;
The willingness to learn is a
choice.
-- Dune: House Harknonnen,
p. 437