2 So How On Earth Did We Get To Where We Are Today? Chemical AnalysisSo How On Earth Did We Get To Where We Are Today?
3 Atoms, Molecules and Ions Science: Atomic Theoryfrom a fundamental understanding of the macroscopic behavior of substances comes an understanding the microscopic behavior of atoms and molecules (Baseball rules from Baseball Game?)Macroscopic MicroscopicSubstances Atomic theoryMixturesPhysical Properties and ChangesQuestion: Can matter be infinitely divided?Most Greek Philosophers - YesDemocritus (460 BC) and John Dalton (1800s) - No (“atomos”means indivisible”)
4 Atoms, Molecules and Ions History of Atomic Theory and Scientific InquiryAristotle - “metaphysics”, thought experiments and no experimental observations necessary to substantiate ideas.Archimedes ( BC) - Scientific Method, determined composition of the King of Syracuse’s crown by measuring density through water displacement.Roger Bacon ( ) - Experimental Science “ It is the credo of free men - the opportunity to try, the privilege to err, the courage to experiment anew. ...experiment, experiment, ever experiment”.
5 Aristotle ( BC)All of the sciences (epistêmai, literally "knowledges") can be divided into three branches: theoretical, practical, and productive. Whereas practical sciences, such as ethics and politics, are concerned with human action, and productive sciences with making things, theoretical sciences, such as theology, mathematics, and the natural sciences, aim at truth and are pursued for their own sake.
6 Archimedes ( BC)Archimedes was a native of Syracuse (not NY). Stories from Plutarch, Livy, and others describe machines invented by Archimedes for the defence of Syracuse (These include the catapult, the compound pulley and a burning-mirror).Archimedes discovered fundamental theorems concerning the center of gravity of plane figures and solids. His most famous theorem gives the weight of a body immersed in a liquid, called Archimedes' principal.His methods anticipated integral calculus 2,000 years before Newton and Leibniz.
8 Archimedes ( BC)Suspecting that a goldsmith might have replaced some of the gold by silver in making a crown, Hiero II, the king of Syracuse, asked Archimedes to determine whether the wreath was pure gold. The wreath could not be harmed since it was a holy object.The solution which occurred when he stepped into his bath and caused it to overflow was to put a weight of gold equal to the crown, and known to be pure, into a bowl which was filled with water to the brim. Then the gold would be removed and the king's crown put in, in its place. An alloy of lighter silver would increase the bulk of the crown and cause the bowl to overflow.Pure Gold?Equal Weight of GoldCrown Displaced More Water
10 Mass Spectrometry Background - Stoichiometry Antoine Lavoisier ( )Law of Conservation of Mass - atoms are neither created nor destroyed in chemical reactionstotal number of atoms = total number of atoms after reaction before reactionStoichiometry - quantitative study of chemical formulas and reactions (Greek; “stoichion”= element, “metron” = measure)Chemical Equations - used to describe chemical reactions in an accurate and convenient fashion2H2 + O2 2 H2Oreactants products
11 Antoine LavoisierAntoine Lavoisier was born in Paris, and although Lavoisier's father wanted him to be a lawyer, Lavoisier was fascinated by science. From the beginning of his scientific career, Lavoisier recognized the importance of accurate measurements. He wrote the first modern chemistry (1789) textbook so that it is not surprising that Lavoisier is often called the father of modern chemistry. To help support his scientific work, Lavoisier invested in a private tax-collecting firm and married the daughter of one of the company executives. Guillotined for his tax work in 1794.
12 “Chemical” Family Trees James T. Spencer(1984, Iowa State University)John G. Verkade(Harvard University,1960)Theron Standish Piper(Harvard University, 1956)Russell N. Grimes(University of Minesota)Harry Julius Emeleus(Imperial College London, 1926)Geoffrey Wilkinson(Imperial College London, 1941)William N. Lipscomb(Caltech., 1945)Alfred E. Stock(Univ. of Berlin ca 1900Linus Pauling(Caltech, 1925)Henri Moissan(University of Paris, 1879)Emil Fisher(University of Strassbourg, 1874)Edmond Fremy(University of Paris, 1856)Joseph L. Gay Lussac(University of Paris, 1800)Adolf von Baeyer(University of Berlin, 1858)Claude L. Berthollet(University of Paris, 1778)August Kekule(University of Gressen, 1852)Jean Bucquet(University of Paris, 1770)Justus Liebig(University of Erlangen, 1822)Red borders indicate Nobel Laureates (first award 1901)Antoine Lavoisier(University of Paris, 1764)
13 Forensic Chemical Analysis Typical Chemical Problems Problem - An unknown sample of a white powered compound is brought into the lab after a routine traffic stop. What is the compound?Problem - A murder is committed with a lead pipe (in the conservatory) that was removed from the bathroom sink. Col. Mustard was found with a deformed lead pipe. Were the two one unit in the past?Problem - A fiber found on a hairbrush appears to be from a wig. Did the fiber come from the wig of the victim or from another source (possibly the murderer)?Problem - Was Napoleon murdered?
14 Analytical MethodsQuestions to consider in choosing an analytical (chemical) method:Quantitative or qualitative requiredSample size and sample preparation requirementsWhat level of analysis is required (e.g., ± 1.0% or ± 0.001%)Detection levels and useful analytical concentration rangesDestructive or non-destructiveAvailability of instrumentationAdmissibility (e.g., are all lead pipes compositionally the same or are there sufficient variations among “known” Pb pipes of the world to link two samples)
15 Spectroscopy and Spectrometry Mass Spectrometry (MS)Atomic SpectroscopyAtomic Absorption (AAS) and Emission Analysis (AES)Neutron Activation Analysis (NAA)Molecular SpectroscopyElectronic SpectroscopyVibrational SpectroscopyNuclear Magnetic Resonance (NMR or MRI)X-ray MethodsX-ray Diffraction (XRD and CAT)Energy Dispersive X-ray Fluorescence (EDXRF)
16 Comparison of Techniques Qual.* or Quant.Sample SizeDetection levelsDestructiveInstr. Avail.Mass Spec.Qual.0.1 mL to 10-8 mL*YesEasyInfrared0.001 gNoUV-visibleAESQuant.10-4 g/LModerateAASNAA1 x 10-9 gPossiblyDifficult* Primary use is in qual. analysis, although it can be used quantitatively in some cases.
17 Mass SpectrometryChemical Background (mass scale, ave. atomic masses, etc.)Instrumental Principles and DesignSpectral FeaturesSpectral Interpretation and ComparisonGC-MS and LC-MS
18 Underlying Ideas - Atomic and Molecular Weights Mass SpectrometryUnderlying Ideas - Atomic and Molecular WeightsAtomic Mass Scale - based upon 12C isotope. This isotope is assigned a mass of exactly 12 atomic mass units (amu) and the masses of all other atoms are given relative to this standard.Most elements in nature exist as mixtures of isotopes.
19 Underlying Ideas - Atomic Weights Mass SpectrometryUnderlying Ideas - Atomic WeightsAverage Atomic Mass (AW)- weighted average (by % natural abundance) of the isotopes of an element.Example (1); B is 19.78% abundant with a mass of amu 11B is 80.22% abundant with a mass of amutherefore the average atomic mass of boron is; (0.1987)(10.013) + (0.8022)(11.009) = amuAlthough natural B does not actually contain any B with mass 10.82, it is considered to be composed entirely of mass for stoich.
20 Underlying Ideas - Atomic Weights Mass SpectrometryUnderlying Ideas - Atomic WeightsAverage Atomic Mass (AW)- weighted average (by % natural abundance) of the isotopes of an element.Example (2): Pt is 33.90% abundant with a mass of amu 195Pt is 33.80% abundant with a mass of amu 196Pt is 25.30% abundant with a mass of amu 198Pt is 7.210% abundant with a mass of amutherefore the average atomic mass of platinum is;(0.3390)( ) )( ) + (0.2530)( ) +( )( )= amu
21 Mass Spectrometry Basic Ideas A mass spectrometer (MS) creates charged particles (ions) from gas phase molecules.Electron Ionization (EI)- Uses electron impact to ionize a molecule.Chemical Ionization (CI)- First ionizes a molecular gas (such as methane) which in turn ionizes the molecule of interest. A “gentler” method of ionization - often allows the observation of a “sensitive” molecular ion as a P+1 peak.Fast Atom Bombardment (FABS)- Mainly for involatile compounds - very harsh.The MS analyzes those ions to provide information about the molecular weight of the compound and its chemical structure.
22 Mass Spectrometry Basic Ideas Either move slit or change deflecting force to scan masses “across” the detector
23 Magnetic field deflection (quadrupole MS) Mass SpectrometerMagnetic field deflection (quadrupole MS)Direct methods of measuring (separating) mass.Sample molecules are ionized by e-beam to cations (+1 by “knocking off” one electron) which are then deflected by magnetic field - for ions of the same charge the angle of deflection in proportional to the ion’s massvacuum chamberbeam of pos. ionsMassSpectrumaccelerating grid (-)NInt.HgsampleS200mass number (amu)focusing slitsionizing e- beammagnetic fielddetector
24 Mass Spectrometer Cl C P Atomic Spectra 35Cl: 75% abundant SpectrumMassSpectrumMassSpectrumInt.Int.Int.ClCP3531123713mass number (amu)mass number (amu)mass number (amu)35Cl: 75% abundant37Cl: 24% abundant12Cl: 98.9% abundant13Cl: 1.11% abundant31P: 100% abundant
27 Mass SpectrometryIonization produces singly charged ions. The intact charged molecule is the molecular ion. Energy from the electron impact and instability in a molecular ion can cause that ion to break into smaller pieces (fragments).The methanol ion may fragment in various ways, with one fragment carrying the charge and one fragment remaining uncharged. For example:CH3OH+. (molecular ion) CH2OH+(fragment ion) + . H(or) CH3OH+.(molecular ion) CH3+(fragment ion) + .OH
33 Mass SpectrometerMS LibraryCaffeineMS of Unknown
34 Mass Spectrometer Mass Spectrum Caffeine Unknown white powdery substance ingested by unconscious patient.What do you do?Mol. Wgt= 194Mass SpectrumCaffeine
35 GC-Mass SpectrometryA mixture of compounds to be analyzed is injected into the gas chromatograph (GC) where the mixture is vaporized in a heated chamber. The gas mixture travels through a GC column, where the compounds become separated as they interact with the column. Those separated compounds then immediately enter the mass spectrometer.
37 Atomic and Molecular Spectroscopy Science: Atomic Theory“The strength of a science is that its conclusions are derived by logical arguments from facts that result from well-designed experiments. Science has produced a picture of the microscopic structure of the atom so detailed and subtle of something so far removed from our immediate experience that it is difficult to see how its many features were constructed. This is because so many experiments have contributed to our ideas about the atom.”B. Mahan from University Chemistry
38 Atomic and Molecular Spectroscopy Electromagnetic RadiationAtomic Electronic StructureQuantization of Energy LevelsAbsorption, Transmission and Emission SpectraAtomic SpectroscopyMolecular Spectroscopy
39 Hydrogen Emission Red Blue Ultraviolet 434.0 nm656.3 nm486.1 nm410.2 nm364.6 nmRedBlueUltravioletA Swiss schoolteacher in 1885 (J. Balmer) derived a simple formula to calculate the wavelengths of the emission lines (purely a mathematical feat with no understanding of why this formula worked)frequency = C ( ) where n = 1, 2, 3, etc...22 n2 C = constant
41 Electromagnetic Radiation where = wavelength, = frequency, c = light speedGammaX-rayUV/VisInfraredMicrowaveRadioWavelength (m)10-11m10 m
42 Electromagnetic Radiation Magnetic and Electronic Partsmutually perpendicular
43 Spectroscopy Electronic Structure - Background Prior to 1926, Many experiments in the structure of matter showed several important relationships:Light has BOTH wavelike and particulate (solid particle-like) properties.Even solid particles display BOTH wavelike and particulate properties.Whether the wavelike or particulate properties are predominantly observed depends upon the nature of the experiment (what is being measured).
44 Wave Properties of Matter De Broglie - particles behave under some circumstances as if they are waves (just as light behaves as particles under some circumstances). Determines relationship: = h/mv = wavelengthh = Planck’s const.m = massv = velocityParticle mass (kg) v (m/sec) (pm)electron 9 x xHe atom (a) 7 xBaseballfast ball x 10-22slow ball x 10-20
45 Niels Bohr (Denmark)Built upon Planck, Einstein and others work to propose explanation of line spectra and atomic structure.Nobel Prize 1922Worked on Manhattan ProjectAdvocate for peaceful nuclear applications
46 Bohr’s Model Continuous Spectra vs. Line Spectra Wave-like Wave-like BehaviorWave-likeBehaviorSunlightHydrogenDispersion by PrismDispersion by Prism
47 Bohr’s Model “Microscopic Solar System” n=∞Electrons in circular orbits around nucleus with quantized (allowed) energy statesWhen in a state, no energy is radiated but when it changes states, energy is emitted or gained equal to the energy difference between the statesEmission from higher to lower, absorption from lower to highern=4n=3n=2electronic transitionsn=1
48 Hydrogen Emission Red Blue Ultraviolet 434.0 nm656.3 nm486.1 nm410.2 nm364.6 nmRedBlueUltravioletA Swiss schoolteacher in 1885 (J. Balmer) derived a simple formula to calculate the wavelengths of the emission lines (purely a mathematical feat with no understanding of why this formula worked)frequency = C ( ) where n = 1, 2, 3, etc...22 n2 C = constant
50 Microscopic Properties Light energy may behave as waves or as small particles (photons).Particles may also behave as waves or as small particles.Both matter and energy (light) occur only in discrete units (quantized).Quantized(can stand only on steps)Non-Quantized(can stand at any position on the ramp)
51 What is QuantizationExamples of quantization (when only discrete and defined quantities or states are possible):Quantized Non-QuantizedPiano Violin or GuitarStair Steps RampTypewriter Pencil and PaperDollar Bills Exchange ratesFootball Game Score Long Jump DistanceLight Switch (On/Off) Dimmer SwitchEnergyMatter
52 Quantum NumbersQuantum Numbers also specify energy of the occupying electrons,n = ∞l = 0l = 1l = 2l = 34s4p4d4fn = 43s3p3d32 electrons maxn = 32s2pENRGYn = 218 electrons max8 electrons maxn2 electrons maxl1sn = 1
53 Many Electron Atoms n = 1 n = 2 n = 3 n = 4 n = 5 5s 4p 3d 4s 3p 3s 2p 5s4p3d4s3pENRGY3s2ps (l = 0)p (l = 1)d (l = 2)2s1s
54 Hydrogen Emission Red Blue Ultraviolet 434.0 nm656.3 nm486.1 nm410.2 nm364.6 nmRedBlueUltravioletNo Just Emission - molecules (and atoms) can also absorb energy.
55 SpectroscopyWhen electromagnetic radiation passes through a substance, it can either be absorbed or transmitted, depending upon the structure of the substance.When a molecule absorbs radiation it gains energy as it undergoes a quantum transition from one energy state (Einitial) to another (Efinal).The frequency of the absorbed radiation is related to the energy of the transition by Planck's law: Efinal - Einitial = E = hn = hc/l .
56 Atomic SpectroscopyAtomic Absorption and Emission- Techniques that involve the determination and measurement of atomic energy levels (spectrometry) and chemical identification based on how atoms absorb or emit electromagnetic radiation.Neutron Activation Analysis - Quantitative multi-element analysis of major, minor, trace (ppb) and rare elements. The sample is placed in a flux of neutrons and after removal the emissions of the radionuclides produced are measured. Forensic applications include gunshot residues, bullet lead, glass, paint, hair, etc.
57 Atomic SpectroscopyGround state - the lowest energy state of an atom or molecule (most stable state) with regard to the position of the electrons around the nucleusExcited state – results when ground state electrons are excited by energy to higher energy states. Excited states are unstable and an atom in the excited state immediately returns to the ground stateEmission - When an electric current is passed through a gas, the gas emits light. This is due to the change of energy of the gas. The electrons in the atoms of the gas become excited to a higher energy state (the “excited state”) and when they return to the original, low-energy state (“the ground state”), the atoms of the gas emit the excess energy as light.Absorption - This is due to the change of energy of the gas. The electrons in the atoms of the gas become excited by absorbing energy (light).
62 Atomic Emission AESAtomic Emission (AE) - uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration. Analyte atoms in solution are aspirated into the excitation region where they are atomized by a flame, discharge, or plasma. These high-temperature atomization sources provide sufficient energy to promote the atoms into high energy levels. The atoms decay back to lower levels by emitting light. Since the transitions are between distinct atomic energy levels, the emission lines in the spectra are narrow.
63 Atomic Emission Spectroscopy AES Advantages of Inductively coupled plasma (ICP-AES):Multielement analysesDetermination of low concentration, difficult to atomize elementsLess chemical interference due to the high temperature in the plasma employedDetermination of many elements (e.g., Zn, Cu)Great linear detection rangeSupplementary to AAS
65 Atomic Emission AESRussian Icon of St. Nicholas - The pigments present on this mid-19th Century painting were characterized by AES spectroscopy (laser-induced breakdown spectroscopy, LIBS) and Raman microscopy. The identification of pigments on the original work along with those applied in restoration of cracks in the varnish and painting surface were analyzed.
66 Atomic Emission AESLIBS depth profile measurements leave a minute crater in the surface of the art object being studied. This allows stratagraphic information to be collected. A typical cross section of the icon is shown.
67 Atomic Emission AESSeveral areas of the icon, where white paint was used, were analyzed. The LIBS spectrum showed strong peaks characteristic of lead. This was confirmed by the Raman spectrum, which verified the presence of lead carbonate, [2PbCO3·Pb(OH)2].LIBSRaman
68 Atomic Emission AESThe brown pigment was characterized as an iron-based pigment mixed with lead white. The pigment scattered poorly and so did not produce a Raman spectrum. The LIBS spectrum showed the presence of Fe and Al, corresponding to an iron oxide and an earth such as clay. Also present are emissions characteristic of magnesium, lead and calcium. The peak corresponding to iron at ~275nm is characteristic of iron that has been observed in studies on pure iron oxide pigments (for example, Mars black, Fe3O4).
69 Atomic Absorption AASAtomic Absorption - Atomic-absorption (AA) spectroscopy uses the absorption of light to measure the concentration of gas-phase atoms. Since samples are usually liquids or solids, the analyte atoms or ions must be vaporized in a flame or graphite furnace. The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels. The analyte concentration is determined from the amount of absorption.
70 Atomic Absorption AASTypical Problem - A child becomes quite ill and is taken to the hospital. It is found that the child is suffering from lead poisoning. A forensic laboratory is contacted and asked if it can determine the source of the lead which the child has ingested. No crime has been committed, per se, but the source must be eliminated to prevent future danger to the child. Paint samples from a number of objects with which the child has had repeated contact are collected. Paint on the child's crib, paint from his toys, and paint from the child's swing, to name a few, are sent to the laboratory. AA is the best method for these analyses.
71 Neutron Activation Analysis NAA Neutrons interact with a target nucleus to form a compound nucleus in an excited state. The compound nucleus will decay into a more stable configuration through emission of one or more gamma rays. This new configuration may yields a radioactive nucleus which also decays by emission of delayed gamma rays, but at a much slower rate according to the unique half-life of the radioactive nucleus.
72 Neutron Activation Analysis NAA NAA falls into two categories: (1) prompt gamma-ray neutron activation analysis (PGNAA), where measurements take place during irradiation, or (2) delayed gamma-ray neutron activation analysis (DGNAA), where the measurements follow radioactive decay (most common). About 70% of the elements have properties suitable for measurement by NAA.Parts per billion or better.Gamma-ray spectrum showing medium- and long-lived elements measured in a sample of pottery irradiated for 24 hours, decayed for 9 days, and counted for 30 minutes on a HPGe detector.
73 Neutron Activation Analysis NAA An example of the gamma-ray spectrum from the activation of a human nail used as a biological monitor of trace-element status.
74 Neutron Activation Analysis Arsenic in Hair Napoleon BonaparteOne of the most brilliant individuals in history, Napoleon Bonaparte was a masterful soldier, grand tactician, sublime statesman and exceedingly capable administrator. After an extraordinary career, he was finally defeated and exiled to Elba. He returned from Elba to be ultimately defeated atWaterloo. He was finallyexiled to the remote tinyvolcanic island of St. Helena,south of the Equator. Thenearest land is AscensionIsland, 700 miles to the north.
75 Neutron Activation Analysis Arsenic in Hair Murdered or Not?For years a controversy has raged about Napoleon being killed on St. Helena - either by French Royalists, persons in his exiled entourage or the British - and all have pointed to the high levels of arsenic in the emperor's body as being evidence of such behavior. The emperor's body contained some 15 parts per million of the poison, where the maximum safe limit is only three parts per million. The determination was by neutron activation analysis of his hair.
76 Neutron Activation Analysis Arsenic in Hair “So Who Done It?”(if it was done at all)British Authorities - The Allied heads of state had no greater wish than to ensure that Napoleon was permanently “out of the way”. Strong hatred by British local commander.Royalists - Revenge and insurance against Napoleon for declaring himself Emperor and dismantling the aristocracy.Exiled Entourage - Jealousy (romantic triangles), intrigue, revenge.
77 Neutron Activation Analysis Arsenic in Hair NAA of Napoleon’s HairFrom the old tradition of keeping hair locks, many sample of Napoleon’s hair are known. NAA showed high concentrations of As at various locations along hair shafts. The As, however, was determined not to have been taken orally.So how did he die and why did he have such high As concentrations?
78 Neutron Activation Analysis Arsenic in Hair The wallpaper in his room was dyed with Scheele's Green (Paris Green), a coloring pigment that had been used in fabrics and wallpapers from around Named after the Swedish chemist who invented it, the dye contained copper arsenite. It was discovered that if wallpaper containing Scheele’s Green became damp, the mould converted the copper arsenite to a poisonous vapor form of arsenic. Breathing the arsenic on its own might not have been enough to kill Napoleon, but he was ill already with a stomach ulcer/cancer. On the 5 May 1821, the arsenic tipped the scale against "the little corporal."
79 Salem Witch TrialsFrom June through September of 1692, nineteen men and women, all having been convicted of witchcraft, were carted to Gallows Hill, a barren slope near Salem Village, for hanging. Another man of over eighty years was pressed to death under heavy stones for refusing to submit to a trial on witchcraft charges. Hundreds of others faced accusations of witchcraft. Dozens languished in jail for months without trials. Then, almost as soon as it had begun, the hysteria that swept through Puritan Massachusetts ended.
80 Salem Witch TrialsIn February of the exceptionally cold winter of 1692, young Betty Parris became strangely ill. She dashed about, dove under furniture, contorted in pain, and complained of fever. Cotton Mather had recently published a popular book, "Memorable Providences," describing the suspected witchcraft of an Irish washerwoman in Boston, and Betty's behavior mirrored that of the afflicted person described in Mather's widely read and discussed book. It was easy to believe in 1692 in Salem, with an Indian war raging less than seventy miles away (and many refugees from the war in the area) that the devil was close at hand. Sudden and violent death occupied minds. Talk of witchcraft increased when other playmates of Betty, including eleven-year-old Ann Putnam, seventeen-year-old Mercy Lewis, and Mary Walcott, began to exhibit similar unusual behavior. When his own nostrums failed to effect a cure, William Griggs, a doctor called to examine the girls, suggested that the girls' problems might have a supernatural origin. The widespread belief that witches targeted children made the doctor's diagnosis seem increasing likely.
81 “Trial of George Jacobs” (1692) Salem Witch Trials“Trial of George Jacobs” (1692)“Examination of a Witch”
83 ErgotErgot - A toxic fungus, ( Claviceps purpurea ) found as a parasite on grains of rye. One form is hallucinogenic ergotism, in which people often experience symptoms of one of the other forms of ergotism (gangrenous ergotism - people experience nausea, and pains in the limbs, bodily extremities turn black, dry and become mummified, makingit possible for infected limbs to spontaneously break off at the joints, or convulsive ergotism) along with vivid hallucinations. The other symptoms are very much like those of modern psychedelic drugs such as nervousness, physical and mental excitement, insomnia and disorientation. People with this form of ergotism were also observed to perform strange dances with wild, jerky movements accompanied by hopping, leaping and screaming. They would dance compulsively until exhaustion lead them to collapse unconscious.
84 Ergotism?St. Christopher Carrying the Christ Child through a Sinful World, Bosch, c1520
85 ErgotismErgotamine tartrateErgot on grains of rye
87 Molecular Spectroscopy Electronic SpectroscopyVibrational SpectroscopyNuclear Magnetic Resonance Spectroscopy (NMR or MRI)
88 Electronic Spectroscopy UV-visible When white light passes through or is reflected by a colored substance, a characteristic portion of the total wavelengths is absorbed. The remaining light will then assume the complementary color to the wavelength(s) absorbed.The remaining light will then assume the complementary color to the wavelength(s) absorbed.
89 Electronic Spectroscopy UV-visible Visible region of the spectrum has photon energies of 36 to 72 kcal/mole, and the near ultraviolet region 72 to 143 kcal/mole (200 nm).Sufficient E to excite a molecular electron to a higher energy orbital.Of the six transitions outlined, only the two lowest energy ones (left-most, colored blue) are achieved by these energies ( nm). Energetically favored electron promotion will be from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO).
90 Electronic Spectroscopy UV-visible When sample molecules are exposed to light having an energy that matches a possible electronic transition within the molecule, some of the light energy will be absorbed as the electron is promoted to a higher energy orbital. An optical spectrometer records the wavelengths at which absorption occurs, together with the degree of absorption at each wavelength.
91 Electronic Spectroscopy UV-visible Effect of Conjugation
93 Vibrational Spectroscopy Infrared and Raman Spectroscopy Radiation from 500 to 4000 cm-1 (vibrational transitions in the molecules).Vibrational “mode” must have a change in dipole moment in the transition. Energy of the transition is dependent upon the strengths of the bonds and geometric structure.
94 Vibrational Spectroscopy Infrared and Raman Spectroscopy For the water molecule, for which there are three vibrational modes, there are consequently three sets of energy levels within which transitions may occur (shown ).The spacing between energy levels depends upon the particular vibration being considered. Each spacing requires a photon of different energy to cause the transition, so we expect photons of three different energies to be absorbed by H2O.
95 Vibrational Spectroscopy Infrared and Raman Spectroscopy In order for a particular vibrational mode to directly absorb infrared electromagnetic radiation, the vibrational motion associated with that mode must produce a change in the dipole moment of the molecule.There are many molecules which, although possessing no permanent dipole moment, still undergo vibrations which cause changes in the value of the dipole moment from 0 to some non-zero value. Consider the CO2 molecule:
97 Vibrational Spectroscopy Infrared and Raman Spectroscopy Different types of bonds have characteristic regions of the spectrum where they absorb
98 Vibrational Spectroscopy Infrared and Raman Spectroscopy Forensic Applications of Infrared SpectroscopyUse of computer databases of IR’s of known compoundsAnalyzing Alcohol - The breath is tested with a mechanism similar to a breathalyzer (chemical oxidation) but uses the infrared absorptions of alcohol.
99 Vibrational Spectroscopy Infrared and Raman Spectroscopy Forensic Applications of Infrared SpectroscopyUse of computer databases of IR’s of known compoundsAnalyzing Drugs - The drug's various chemical components absorb infrared light. The absorptions are compared to known samples using a database.
100 Vibrational Spectroscopy Infrared and Raman Spectroscopy Forensic Applications of Infrared SpectroscopyUse of computer databases of IR’s of known compoundsAnalyzing Fibers - The expected identity of the fiber has been established by observing it under a microscope. Its IR spectrum can confirm the suspected identity.
101 Vibrational Spectroscopy Infrared and Raman Spectroscopy Forensic Applications of Infrared SpectroscopyUse of computer databases of IR’s of known compoundsAnalyzing Paint - Paint has been recovered from a crime scene. Since there is a limited amount of paint, the first tests to be done should be nondestructive. Colors, layers, texture, and other physical properties are recorded. The individual layers of paint are analyzed by infrared spectroscopy. The results can be compared to IR results of known paint samples.
102 Infrared Spectroscopy “With infrared radiation, forensic scientists can determine the exact ink type and pen that a death threat was written in, or the very model and year of a suspect's automobile in a hit-and-run accident. Using a technique known as infrared spectromicroscopy, forensic investigators have been able to identify and analyze a broad range of samples—from inks and paint chips to fibers and drugs. The procedure uses infrared light to study the properties of molecules at an atomic resolution. Researchers at Lawrence Berkeley National Laboratory have now expanded the boundaries of infrared forensics with the use of synchrotron radiation from the Lab's Advanced Light Source (ALS) facility…..” (Daily Californian, Wednesday, September 18, 2002)
103 Magnetic Resonance Spectroscopy NMR (MRI) Visualize soft tissue by measuring proton (nuclear) magnetic alignments relative to an external magnetic field.Review Electron Spin Properties First.
104 Electron spin is quantized Electrons have spin properties (spin along axis).Electron spin is quantizedms = + 1/2 or - 1/2N--NMagnetic Fields
105 Experimental Electron Spin Passing an atomic beam (neutral atoms) which contained an odd number of electrons (1 unpaired electron, see later) through a magnetic field caused the beam to split into two spots.Showed the possible states of the single (unpaired) electron as quantized into ms = +1/2 or - 1/2.two electron spin statesViewing ScreenMagnetic FieldAtom Beam GeneratorSlitsNS
106 Nuclear SpinLike electrons, nuclei spin and because of this spinning of a charged particle (positively charged), it generates a magnetic field. Two states are possible for the proton (1H).NS++SN
107 Similar to a canoe paddling either upstream or downstream Nuclear SpinSimilar to a canoe paddling either upstream or downstreamSAntiparallelDegenerateENNSNParallelSSNExternal Magnetic Field
108 Magnetic Resonance Imaging MRI Hydrogen atom has two nuclear spin quantum numbers possible (+1/2 and -1/2).When placed in an external magnetic field, 1H can either align with the field (“parallel” - lower energy) or against the field (“antiparallel” - higher energy).Energy added (E) can raise the energy level of an electron from parallel to antiparallel orientation (by absorbing radio frequency irradiation).Electrons (also “magnets”) in “neighborhood” affect the value of E (i.e., rocks in stream).By detecting the E values as a function of position within a body, an image of a body’s hydrogen atoms may be obtained.
109 MRI Advantages (first three are not really important for forensics) non-invasive.no ionizing or other “dangerous” radiation (such as X-rays of positrons).Can be done frequently to monitor progress of treatment.images soft tissues (only those with hydrogen atoms (almost all “soft” tissues).images function through the use of contrast media.DisadvantagesRelatively expensive equipment.
117 Forensic MRI/CTUsed to reconstruct facial images from skulls. Use for ancient mummies to modern skulls.Allows a very fine discrimination between materials with different densities providing an enormous amount of information about the mummy and its skeleton.The level of automation reached in building models from CT data, reconstruction, texture application and visualization allow to the user to complete whole process in 2-3 hours on a PC or graphic workstation.
118 Forensic MRI and CT The “Virtopsy” focuses on four goals: radiological digital imaging methods as main diagnostic tools in forensic pathology, ultimately leading to "minimally invasive autopsy" analogous to "keyhole surgery" in clinical medicine.three-dimensional optical measuring techniques - a reliable, accurate geometric presentation of all forensic findings (the body surface as well as the interior).3D surface scanning in forensic reconstruction.Producing and validating of a post-mortem biochemical profile to estimate the time of death.The implementation of an imaging database as a technical basis of a "center for competence in virtual autopsy”.
119 Forensic MRIVirtopsy, a new imaging horizon in forensic pathology: virtual autopsy by postmortem multislice computed tomography (MSCT) and magnetic resonance imaging (MRI) - 40 forensic cases were examined and findings were verified by subsequent autopsy. Results were classified as follows: (I) cause of death, (II) relevant traumatological and pathological findings, (III) vital reactions, (IV) reconstruction of injuries, (V) visualization. In these 40 forensic cases, 47 partly combined causes of death were diagnosed at autopsy, 26 (55%) causes of death were found independently using only radiological image data. Radiology was superior to autopsy in revealing certain cases of cranial, skeletal, or tissue trauma. Some forensic vital reactions were diagnosed equally well or better using MSCT/MRI. Radiological imaging techniques are particularly beneficial for reconstruction and visualization of forensic cases.(J Forensic Sci. 2003, 48, )
120 Forensic MRI Validating of a post-mortem analysis Complex scull fracture system following motor vehicle accident (victim was overrun by automobile). 3D reconstructed MSCT - image.
121 Forensic MRI Validating of a post-mortem analysis Injury due to vehicle impact in a motor vehicle accident (pedestrian). (right) finding at autopsy; right lower leg showing fracture of the fibula. (left) 3 D reconstructed MSCT;
122 Forensic MRI and CT Facial Reconstructions Egyptian Mummy HeadThe method uses the tables combined with the warping of a 3D model of a reference scanned head, until the relevant surface to bone distances are correct. Texture mapping is used to provide colors and aesthetic features.
123 Forensic MRI and CT Mummy Facial Reconstruction Model skin (blue) and mummy skull (white)Face shape generated
124 Forensic MRI and CT Mummy Facial Reconstruction Texturized model of reconstructed soft tissues of the mummy
125 X-ray Methods X-ray Diffraction (XRD and CT) Energy Dispersive X-ray Fluorescence
126 Bragg’s Law and X-ray Diffraction incominglightElattice in a crystaldBDCSince BCD = 2d sin is the limiting condition for observing a reflection then because of wave addition and cancellation;Bragg’s Law:n = 2d sin where n = 1, 2, 3, etc...
128 Energy-Dispersive X-ray Fluorescence (EDXRF) Did your luxury purchase originate in a mine deep in the heart of Central America, or the bottom of a silty river tributary in Africa, or perhaps even a flask in a laboratory in Chicago or Minsk?Metal ions such as V3+, Cr3+, Mn2+, Mn3+, Fe2+, Fe3+, Ni2+, Cu2+, and UO22+ are responsible for the colors of most common gemstones and minerals.U.S. Federal Trade Commission says consumers must be informed of alterations in gemstones.
129 Energy-Dispersive X-ray Fluorescence (EDXRF) Among the most sensitive and popular of the nondestructive spectroscopic techniques used for trace-metal determination is EDXRF. In this technique, X-rays excite the gemstone to fluoresce and the fluorescent line spectrum indicates which chemical elements are present.EDXRF can also be used to differentiate freshwater from saltwater pearls on the basis of the greater concentration of magnesium present in the former.
130 Energy-Dispersive X-ray Fluorescence (EDXRF) EDXRF has been called 'the curator's dream instrument' because measurements are non-destructive and usually the whole object can be analyzed, rather than a sample removed from one. The technique involves aiming an X-ray beam at the surface of an object; this beam is about 2 mm in diameter.The interaction of X-rays with an object causes secondary (fluorescent) X-rays to be generated. Each element present in the object produces X-rays with different energies. These X-rays can be detected and displayed as a spectrum of intensity against energy: the positions of the peaks identify which elements are present and the peak heights identify how much of each element is present.
131 Energy-Dispersive X-ray Fluorescence (EDXRF) An incoming X-ray ejects a K-shell electron from an atom of the target. An electron in the M or L-shell loses energy as it transitions to the vacant K-shell. It given off energy in the form of fluorescence.
133 Analytical MethodsQuestions to consider in choosing an analytical (chemical) method:Quantitative or qualitative requiredSample size and sample preparation requirementsWhat level of analysis is required (e.g., ± 1.0% or ± 0.001%)Detection levels and useful analytical concentration rangesDestructive or non-destructiveAvailability of instrumentationAdmissibility (e.g., are all lead pipes compositionally the same or are there sufficient variations among “known” Pb pipes of the world to link two samples)