Physics and Mass Spectrometry»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

Scanning luggage in airports Explosives and narcotic trace detection is

paramount

Scanning luggage in airports

© Copyright UA International Limited. All rights reserved.

Mass spectrometry in air travel safetyCarry-ons scanned! Safe to fly?

Source: Southwest Airlines Co.

Mass spectrometry in the labs

“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)

What is mass spectrometry?

Physics in mass spectrometry definition» 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 timeCharge- 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.

Samples for Mass spectrometryIn research and pharmaceutical

industries, molecules of interest include proteins, sugars, DNA, drugs, and many other biologically relevant molecules

Samples for Mass Spectrometry» Samples are specially prepared before analysis by Mass

Spectrometry» They may include:» Blood, Urine, Drugs etc.

Units in Mass Spectrometry»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?)

Mass spectrometry basic theoryExamination 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)

Basic Physics in Mass spectrometry»3 Basic Steps ˃Ion source˃Mass analysis˃Detection

Source: Select Science

Why in Vacuum?» Rocket Launching! Recent Physics lesson

The Rockets!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

Reduction of “Frictional Drag” 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

Ionization» 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 analysis 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)

Compare the rockets Vs. the Wind! 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!

Ion Mobility

» Ions analyzed according to their speed» What physics that is employed here?˃Vd = The ion’s drift velocity

˃dd= Ion’s drift distance

˃ td = Ion’s drift time

Vd

Ion mobility» An inert gas like Helium is used as the drift gas» An important formula that helps analyze the ions is

» 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

𝝁=𝑚1𝑚2𝑚1+𝑚2

DetectionMore 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

Application!Walk through trace detection portals

» 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

Mass spectrometry in air travel safetyHeavily employed for military or security purposes such as

detecting drugs and explosives

The endThe 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