Test Two Study Guide
Test Two Study Guide FRSC 367
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This 6 page Study Guide was uploaded by Kayli Antos on Saturday October 10, 2015. The Study Guide belongs to FRSC 367 at Towson University taught by Mark Profili in Summer 2015. Since its upload, it has received 35 views. For similar materials see Forensic Chemistry in Criminology and Criminal Justice at Towson University.
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Date Created: 10/10/15
Forensic Chem Test 2 Gas Chromatography Pyrolysis is the rapid vaporization of certain solid analytes at very high temperatures so they can be run through the GC Chromatograph measures retention time of the components Can be used to quantify a substance but not qualify It separates them for identification Relative retention times between two compounds will never change Some solid analytes drugs can be dissolved in methanol before they re vaporized seen on the chromatograph A methane and air peak will be The most common detector is the flame ionization detector Decreasing the temperature in the column can increase the separation between peaks Quantitative C The amount of substance passing through the GC detector is proportional to the peak area recorded C Can run a known amount and compare areas under peaks Factors That Determine Retention in GO C The retention time is the relative time the analyte spends in the mobile phase as opposed to the stationary phase Volatility temperature and polarity affect retention time More volatile compound will elute first C The Kovats Retention Index I is the retention time of the analyte compared to the retention time of a series of alkanes under the same conditions Instruments For GC C Carrier Gas Supply and H gauges C Common carrier gases are He N C There are pressure regulators meters and flow C Sample Injection Port C There cannot be too much sample or else the top of the peaks will be off the charts C C The whole sample must be injected as quickly as possible The most common injector port is a flash vaporizer that has a self sealing septum C Column Configurations C C There are packed columns and open tubular columns Can be shorter than to meters or longer than fifty meters They can be made of stainless steel fused silica or Teflon glass C Column Ovens C C Can control the temperature to the tenth of a degree The best elution time occurs when the temperature is equal to or slightly higher than the average boiling point C Detection Systems C An ideal detector should have good sensitivity good stability and reproducibility in results ability to maintain a liner response over a wide range ability to handle temperatures greater than 400 short response time independent of flow rate reliability and ease of use similar response to all solutes or high selectivity to certain classes of solutes ability to not destroy the sample uncommon Detectors C Flame Ionization Detectors FID C C C C C Used for drugs and arson Good for arson because it detects hydrocarbons and also doesn t detect water The effluent is mixed with air and H and ignited Very sensitive and has a large range of detection Destroys sample C ElectronCapture Detectors ECD C Used for environmental samples because it can detect halogen containing compounds PCBs like pesticides and Used for explosives because it can detect N compounds halogens peroxides C B emitter emits electrons that ionize he carrier gas which then emits electrons Organic molecules will capture these electrons and will decrease the current C Cannot detect amines alcohols hydrocarbons GC Columns C Open Tubular Capillary Wall coated open tubular WCOT inside coated with thin layer of stationary phase C Support coated open tubular SCOT inside lined with thin film of support material which holds more stationary phase than WCOT Packed C Two to three meters long two to four nm in diameter Packed with packing material that s coated with stationary phase C Solid Support Materials C Made from diatoms because they have many pores The Stationary Phase Should have low volatility stability at a range of temperatures no chemical interactions with analyte C Should interact with the analyte enough to retard its elution from the column Mass Spectrometry Expensive but reproducible reliable and identifies compounds Can be a GC detector Gives mass spectrum Basic Principle C Can find the mass of the particle if you know initial speed magnitude of the sideways force path along which the particle travels What Happens In MS C Atoms can be deflected by a magnetic field is they are ionized and the curved C Ionization occurs in the ionization chamber Acceleration And Deflection All ions are accelerated o the same kinetic energy Then subjected to a magnetic field which deflects them C The amount of deflection depends on the mass to charge ratio C After acceleration they pass through slits to concentrate them Detection C A vacuum pumps out air molecules and some extra ions and atoms that became unionized C The resulting beam is then detected electronically Ionization C In the ionization chamber there s a metal coil which is heated electronically It emits electrons which ionize and fragment the sample C Tons are then pushed through the MS by a positively charged plate that repels them Uses C Provides clues to the structure of the original molecule based on the ionization and fragmentation Also provides the molecular weight Background C The mass spectrum compares the mz ratio to relative abundance C The most abundant is given a relative abundance of 100 and all other peak are given a relative abundance of a percentage of 100 Fragmentation Patterns of Alkanes C loss of methyl Mi lS C loss of ethyl M3 29 C loss of propyl Mi 43 C loss of butyl Mi 57 Rule Of Thirteen Used for hydrocarbons lt3 C h1nMi13 and mremainder IR What is IR Light C Between visible light and radio waves What is the IR region C C C Wavelength from 25 to 25 um Wavenumbers from 400 to 4000 cm n Wavenumber is proportional to energy and frequency and reciprocal to wavelength Principles C C When certain molecules are hit with IR light absrb energy and their atoms vibrate they The frequency of vibration depends on the amount of atoms in the molecule and how ong nd stong the bond is Energy Trends C C C C C Lighter atoms vibrate more rapidly than heavier atoms C H N H 0 H bonds vibrate at 2800 cm l Double and triple bonds vibrate more rapidly than single bonds CEC vibrates at 2l00 2200 cm l CEC vibrates at 2240 2280 cm l CO vibrates at l680 l750 cm l CC vibrates at 1620 l680 cm l C O vibrates at l025 l200 cm l Intensity Trends C C C These are the changes in the dipoles that result from the atoms vibrating Polar bonds the strong dipoles will absorb a lot of energy 0 H CO CN C O are some strong dipoles Nonpolar bonds will absorb weaker than the polar bonds CC CEC are some nondipole bonds IR Spectrum Distribution CgtCDlt3 C Bonds to hydrogen 4000 2500 cm l Triple bonds 2500 2000 cm l Double bonds 2000 l500 cm l Fingerprint region l500 400 cm l Procedure C C IR light passes through the sample and the energy absorbed by the sample is measured Monochromator selects type of IR light Interferometer Fourier Transform IR runs all IR at once C Data is processed into a graph of wavelength vs transmission IR Components IR Resources Nernst glower Globar 69 Sample Solids Mortar and Pestle Ground very fine and mixed with liquid paraffin 39Paste placed between two NaCl plates KBr Disk Added to KBr and ground very fine Mechanically compressed Thin Films Placed in holder Calibrate this way using polystyrene Liquids One drop placed between KBr or NaCl plates Gases Placed in special cylindrical cell with windows on each end C MonochromatorInterferometer C Selects certain wave regions to hit the sample with 69 Detector C Charge coupled device CCD C Indium Gallium Arsenide lnGaAs Lead sulfide PbS C Microscope C Can be attached to a microscope but it s cumbersome and expensive Advantages C Proved a unique graph which can be used to identify the substance C If attached to a computer will manually check the spectrum generated against library C Disadvantages C Cannot quantify Sample preparation can be difficult
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