» 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?

» 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= 1.66x 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 ( watch?v=tOGM2gOHKPc) 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(

 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? ˃V d = The ion’s drift velocity ˃d d = Ion’s drift distance ˃t d = Ion’s drift time

» 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

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