Forensics Test 3
How are Wave number and Wavelength related?
(W) = 1/λ -the higher the wavelength the lower the wavenumber
What color differences do we see between blondes, brunettes and red heads?
-Brunettes --Has a loose pattern of eumelanin-filled granules or granules blended with eumelanin and phenomelanin [depends upon warm/cool tones and darkness/lightness]. -Blondes --CONTAINS FEW GRANULES WITHI MINIMMAL BITS OF EUMELANIN; EUMELANIN SO SPARSE THAT THE COLOR OF BLONDE HAIR REPRESENTS THAT OF THE HAIR FIBER ITSELF. -Redheads
Disadvantages of IR
-Cannot be used to examine single atoms. Species must contain a chemical bond. -Homonuclear species (N2,O2...) -It is not useful in complex mixtures. -As water is a strong absorber in the IR aqueous solutions are difficult to analyze.
What type of cuticle's are there and which is most likely to be human?
-Coronal Scales --Found in hairs of very fine diameter and resemble a stack of papers. --Found in small rodents and bats; rarely seen in humans -Spinous Scales --Triangular in shape and protrude from the hair shaft. --Found at the proximal region of mink hairs and on the fur hairs of seals, cats, and some other animals; never found in human hairs. -Imbricate Scales --Consists of overlapping with narrow margins. --Found in human hairs and many animal hairs.
Identify some characteristics that would distinguish between an animal and human hair?
-Coronal/spinous cuticle vs. imbricated cuticle -Medullary index 1/3 or less human; ½ or more animal
What type of information can we get from a hair sample?
-DNA, toxicology (drugs and metals/poisons). -Patterns, roots, color, length, shaft characteristics, hair was forcibly damaged by burning, dyed/ bleached, and cut by glass. -From a human or another animal, from certain body area, from certain racial group, particular growth phase, damaged, diseased, associated with other trace elements, chemically altered (such as dyed or bleached).
Discuss the characteristics of the medulla in human head hair. How does this differ from that found in animals?
-Human hair medulla can be fragmentary or trace, discontinuous or broken, or continuous. -Differ in medullary index. --Human hair is 1/3 or less --Animal hair ½ or more
What advantages does hair analysis have over urine, blood and saliva?
-Long time window for drug detection -Easy to collect, handle and store -- Sample is cut, ground, then washed with water and or solvents. Extraction process precedes assay test. -Storage at room temperature. -- There is no reason to refrigerate samples. Second collection is possible -Noninvasive -Beating this test may be difficult
What disadvantages does drug analysis of hair samples have?
-May not detect recent use -Environmental contamination is a possible problem -Mechanism of drug deposition is not well understood -Due to either diffusion from blood to hair follicle, sweat secretion, sebaceous gland secretion or environmental contamination -Dose/time relationships not well established. -Few controlled studies
What limitations are there on a solvent used in IR?
-Must be transparent in the region to be studied -Water and alcohols are avoided because of the broad O-H band -Must be chemically inert to not react with the analyte or the cell
How might we find IR more useful than UV?
-universal technology used on liquids, solids, and gases -rich source of structural info -fast (<5 min) -easy to use -small sample size -inexpensive (<$10,000) -nondestructive
Provide 5 advantages of Infrared Spectroscopy.
-universal technology used on liquids, solids, and gases -structural info -fast (<5 min) -easy to use -small sample size -inexpensive (<$10,000) -nondestructive
How many bending and how many stretching possibilities are there? Will all of these be IR active?
4 bending -Scissoring (In-plane) -Rocking (In-plane) -Wagging (Out of Plane) -Twisting (Out of Plane) 2 stretching -Symmetric -Asymmetric -Asymmetric stretching and bending IS IR active -Symmetric stretching and bending is NOT IR active
What region of the spectrum is used for IR spectroscopy?
500-4000 cm-1
How are absorption and % transmittance related?
A = log (1/T) -the higher the transmittance the lower the absorbance
What instrument is used in comparing hair samples?
A comparison microscope proves most useful in hair analysis with a magnification of 40x-400x
In each of the following pairs of bonds, select the one that stretches at the highest frequency. A. C-O or C=O B. C-O or C-Cl C. C=C or C≡C D. C-C or C-O E. C-H or O-H
A. C=O B. C-O C. C≡C D. C-C E. O-H
Are these at a high or low energy: A. higher wavenumber B. higher frequency C. long wavelength
A. high energy B. high energy C. low energy
Rank the following bond stretches in order of expected absorption intensity and stretching energy: C-F, C-Cl, C-Br, and C-I.
Absorption intensity depends on polarity and number of bonds present. C-F > C-Cl > C-Br > C-I
How does the absorption of IR affect a molecule?
Absorption of IR changes in the vibrational motions of a molecule. Different vibrational modes include stretching and bending.
What are the 3 growth phases of hair? Which is the most likely to produce a DNA sample?
Anagen, Catagen, and Telogen Anagen
Simply by exchanging an atom of hydrogen (C-H) for deuterium (C-D) we notice a significant change in the stretching vibration. Use the above formula to explain this behavior.
As the atomic mass increases the stretching frequency decreases. Since deuterium is heavier than hydrogen it will have a lower frequency.
Which compound would be expected to show intense IR absorption at 3300 cm-1? A. CH3-CH2-CH3 B. CH3-C≡C-H C. CH3-CH=CH2 D. CH3-CH2-CH2-F
B. CH3-C≡C-H
Which of the following bonds would show the strongest absorption in the IR? A. carbon-hydrogen B. oxygen-hydrogen C. sulfer-hydrogen
B. oxygen-hydrogen O has the highest polarity in relation to H
What problems are caused by carbon dioxide in an IR spectrum? Why is this frequently a problem? How is this problem solved?
Broad peak that are very large. Lab techs breathe into the IR spec releasing CO2. Hold breath when preparing to use the IR spec.
Explain which has a lower characteristic stretching frequency, the C-H or C-D bond?
C-H has a higher stretching compared to C-D. ----higher mass=lower stretching
Rank the following bonds in order of increasing stretching frequency (cm-1) in IR spectroscopy: C-H, C≡C, C-O, and C=O
C-O < C=O < C≡C < C-H
Explain which has a lower characteristic stretching frequency, the C=O bond or the C-O bond?
C=O has a higher stretching compared to C-O. ----stronger bonds=higher stretching
What microscope is most commonly used to examine hair samples?
Comparative Microscope
Why is the hydrogen bond such a broad band in the IR?
Compound has a high number of individual molecules and each may be H-bonded to a different extent. The IR spectrum is acquired IR absorptions occur at varying frequencies for each bond => IR peak appears broadened because it is an average of all these slightly different absorptions.
In order for a vibration to be observed in the Infrared Spectra, the vibration must change the _____ of the molecule.
Dipole
What is the region of the IR spectra called which contains the most complex vibrations?
Fingerprint region
How does hair analysis help in poisoning cases?
Forensic toxicologists can look for toxic metals in hair to explain poor mental and physical health.
How fast does the human head hair grow?
Grow at an average of 1.3 centimeters (cm) every month.
What artificial treatments might we find in hair?
Hair dye
How does hair testing compare to Urine and Blood testing? Is it better/worse and why?
Hair testing is better. The test is highly accurate, detects presence of a variety of drugs, has a prolonged detection period, cannot be easily defeated, etc.
What is responsible for human hair color and where in the hair is this found?
Melanin in two forms eumelanin (pink or blue) and phenomelanin (black or brown); found in pigment granules.
Can a precise probability be assigned to matching a hair sample?
No. The particular individual matching the many characteristics of the hair is unlikely.
It appears at first glance that CO2 would not be IR. However, CO2 is IR active. Explain this seeming contradiction.
Symmetrical stretching doesn't result in a dipole and is IR inactive. However, asymmetrical stretching produces a strong dipole that is IR active.
When recording an IR spectrum in the lab, we take no special precautions to account for the presence of oxygen, nitrogen, or argon in the air. What are the consequences of not compensating for these gases?
There are no consequences for a lack of compensation because O2, N2, and Ar are all non-polar species and their dipole moments don't change during vibration.
Explain the following series: Bond Stretch cm-1 CH 3000 CC 1200 CO 1100 CCl 750 CBr 650
This is an example of mass effect, where the greater the mass the lower the frequency.
What differences do we see on the absorption of energy in the IR versus the UV?
UV/Vis energy is absorbed: we see an electron transition and excitation of ground state electrons. IR is absorbed: stretching and bending of covalent bonds which can reveal info about functional groups
Why are salts such as NaCl, NaBr, KBr used in IR analysis?
Used as salt plates because: -inexpensive -easy to polish -transparent
When does the absorption of water and carbon dioxide in the IR become an issue?
When the sample under study has the same absorption bands at the same wavenumbers => sample bands being masked by water and carbon dioxide => sample detection problems.
What is the relationship between frequency and wavelength?
c= ν λ so there is a indirect relationship
In some detail explain the following formula and what practical implications this formula has in Infrared Spectroscopy. What affect will changes in k and m have on an IR peak. v=1/2pi*sqrt(k/mr)
v = Frequency (cm-1) k = Spring stiffness (Bond Strength) mr = Reduced mass -Frequency increases with decreasing atomic mass -Frequency increases with increasing bond energy
Why is water almost never used as an IR solvent?
water is a strong absorber in the IR and produces a very large broad peak
