jimtrue.com : school : CJT2141 : 05: Organic Analysis
Posted by Jim True on February 5, 2003 7:00 AM. Last Updated October 22, 2006 9:23 PM
Disclaimer for all material noted here is at the bottom of this web page.
(Bold print items in Chapter 5 - Study and know)
Elements -
Compounds - Two or more elements
Carbon, difference between Organic and Inorganic chemistry or compound (if
Carbon is present, compound is Organic).
Big compound, is a Molecule.
98% of the world is INORGANIC, 2% of the entire earth is Organic Material.
99.5% of the compounds that come into the crime labs are Organic in Nature.
(Fingerprints, amino acids).
Smallest particle of an element that can exist and still retain its identity as
that element is the atom.
General ANALYSIS METHODS for Organic Materials, compare, identify and analyze.
1. Chromatography
2. Spectroscopy
Chromatography - (used in Forensic Laboratories)
a. Gas
b. Thin Layer
c. High Pressure Liquid (High Performance)
d. Electrophoresis
Chromatography - Greek 'color writing'
William Henry, p122,
Henry's Law - When a volatile chemical compound is dissolved in a liquid and is
brought to equilibrium with air, there is a fixed ratio between the
concentration of the volatile compound in air and its concentration in the
liquid, and this ratio remains constant for a given temperature.
At a given temperature, some of it wants to be in vapor, some of it wants to be
in liquid.
Chromatography, separate out Organic compounds, Tentative Identification.
Because there is a slight chance another compound will separate at the same
rate, it is TENTATIVE id.
THIN LAYER Chromatography (Different Liquids)
See Fig 5-2
Toxicology
Drug
Questioned Documents (Analyzing Inks)
Dies in fibers
Electrophoresis, horizontal Thin Layer Chromatography, with the addition of
Electricity to assist the separation. (Different Liquids, Energy) DNA,
Serology.
Capillary, smaller scale. Capillary Electrophoresis, CE, thin capillary column.
Less solvent, less electricity, less sample, more separation.
Capillary gas chromatography. More distance, better separation, less solvent.
Less sample.
Gas Chromatography (temperature is the variable)
Material has to be able to be vaporized; pyrolyzing is 'vaporizing the sample'.
HPLC, High Pressure Liquid Chromatography, vary the liquid, to push the
compound through the column and add pressure. Larger pharmaceutical compounds.
Good for explosives, steroids.
Always come out at the same temperature and same rate, Chromatography provides
tentative ID.
Retention Time - How long from when you insert the compound before it comes out
of the column.
Rf - Difference, between the distance the spot travels from the origin and the
distance between the solvent on the plate.
0.1 % of the elements of the Earth is Carbon, but about 98% of the evidence
looked at in a Forensic Lab.
DNA is just a great big organic molecule.
SPECTROSCOPY
Spectroscopy = Spectrophotometry)
a. UV-Vis (Ultraviolet - Visible Light)
b. IR (Infrared)
c. Mass
d. Raman (uses an area between UV-Vis and IR range)
spectro - seeing photo - light metry - measure
Wavelength is distance from peak to a peak or crest to a crest.
Frequency, number of wavelengths over a given unit of time.
Electromagnetic Spectrum - Gamma, XRays, UV, Vis, IR, Micro, Radio
Frequency decreases, wavelength increases; ie a spring coiled tightly has more
energy, stretched out has less energy (greater frequency, less wavelength -
more energy/ less frequency, greater wavelength - less energy).
XRays
UV-Visible
IR (no two compounds will have the identical IR spectrum, in even the different
forms [base powder cocaine, or the rock cocaine form)
Beer's Law: A = kc (Absorbance is equal to Konstant X Concentration)
Concentration, the amount of substance being analyzed.
K - Constant, can be whatever number it is. Absorbence is equal to
concentration. More absorbent, more concentrated the compound is.
By defining the relationship between absorbance and concentration, Beer's Law
permits spectrophotometry to be used as a technique for quantification.
IR (Infrared) - Pure State - Positive ID.
UV-Vis (Ultraviolet - Visible Light) - Tentative ID. A lot of compounds will
give similar spectrum, good for dirty samples - Mixture of compounds.
Differentiate different shades of color.
FT-IR (Fourier Transform Infra Red) - Fourier Transform is a calculus formula.
Several analysis of large spectrum all at once, computer does the analysis.
Instead of 3 minutes to run a spectrum, can run the spectrum in 10 seconds.
Photo Diode Array UV-Visible PDA, one snapshot of entire spectrum, computer
does the separation and clears out the interference.
Mass Spectroscopy - Has to be a separation technique first; GC/MS - Gas
Chromatography does the separation, Mass Spectrometry identifies.
Mass Spectrometer is in a vacuum, bombards the compound with electrons and
always breaks up the compound the same way. Fragments and always fragments the
same way, how it fragments is a total of mass units known as a mass spectrum.
Mass Spectrum (Positive Identification) (Tinker Toy breakdown)
Sample has to be in a pure form (GC does the separation, MS does the analysis
and identification).
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