Presentation on theme: "» 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."— Presentation transcript:
» 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
» 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)http://www.youtube.com/ watch?v=tOGM2gOHKPc
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)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? ˃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