Chemistry Comp Test Answers – Flashcards
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| External Calibration |
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| Set of known concentrations of standards analyzed at the same time as unknowns |
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| Calibration Equation |
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| y = ax + b |
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| Analytical Equation |
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| x = (y-a)/b |
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| Standard Addition |
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| Not used as much Known amounts of standard added to each sample Uses lots of unknown sample |
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| Internal Standardization |
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| Commonly used in toxicology Useful where sample prep leads to loss of analytes Cmpd added to unknown, distinguish IS from analyte of interest Response ratios of analyte to a fixed quantity of IS plotted for multiple calibrators |
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| Resolution |
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| R = 2*(t2-t1)/(Wb2+Wb1) Recommended R ~2.0 |
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| Theoretical Plates |
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| Neff = 5.54(t'R)^2/(W1/2)^2 Efficiency of column |
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| Carrier Gas Effects |
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| Resolution and efficiency Nitrogen- better resolution Helium and Hydrogen- give up resolution, increase ability to have shorter run times |
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| Van Deempter Equation |
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| HETP = A + B/u + C*u |
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| Van Deempter A |
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| Eddy diffusion term Particle size distribution Not as in important in HPLC |
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| Van Deempter B |
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| Longitudinal diffusion term Proportional to time on column Density of mobile phase affects Increasing temperature causes molecules to diffuse more and move faster, B increases |
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| Van Deempter C |
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| Mass transfer term Due to inadequate time for equilibrium between phases Faster flow = less time |
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| Splitless Inlet System |
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| Want maximum sensitivity Use of small sample amount |
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| GC Isothermal Elution |
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| Not useful for complex samples with many compounds over wide BP range Early cmpds bunched, heavier cmpds have long elution times with low peak heights |
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| GC Temperature Programming |
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| Use for samples with wide range of volatility, boiling points, or molecular weights Uses low column temperatures to better separate early cmpds, increasing temps to speed the elution of more retained cmpds (cuts analysis time) |
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| GC Thermal Conductivity Detector (TCD) |
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| Most "universal", not very sensitive (1 ng) Best for fixed gases: N2, O2, CO2, CO |
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| GC Flame Ionization Detector (FID) |
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| "Universal" for most organic compounds (10-100 pg) Not sensitive to fixed gases or water Requires H2 and "Zero Air" for flame Most commonly used (being replaced by MS) Drug quantitation |
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| GC Nitrogen-Phosphorus Detector (NPD) Alkali-Flame Ionization Detector (AFID) Thermoionic |
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Selective for N or P containing cmpds Was often used in drug and tox labs |
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| GC Nitrogen-Phosphorus Detector (NPD) Alkali-Flame Ionization Detector (AFID) Thermoionic |
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| Selective for N or P containing cmpds (10 pg) Drug analysis Being replaced by MS detectors |
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| GC Electron Capture Detector (ECD) |
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| Selective for halogen, nitro, or aromatic cmpds (50 fg) Not used often Contains radioactive source (63Ni) |
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| GC Infrared Detector (GC-IRD) |
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| Universal for most organic cmpds Not as sensitive as other detectors Good for ID of isomers of cmpds where mass spectra are similar |
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| GC-MS |
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| Most widely used instrumental technique in chemistry lab Samples not good- explosives (thermally unstable), low volatility materials, inorganic salts, fibers |
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| Mass Spectrometry- GC Detector |
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| Universal and specific (1 ng and 1 pg) TIC- all ions in range EIC or Selective Ion Monitor- selective |
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| MS Ion Source- Electron Impact (EI) |
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| Most common Ions stream off tungsten filament to target Hit and knock off electron to become positive |
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| MS Ion Source- Chemical Ionization (CI) |
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| Creates positive ion Useful if a weak molecular ion under EI conditions If cmpd fragments a lot |
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| MS Ion Source- Negative Chemical Ionization (NCI) |
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| Creates negative ion Useful for explosives |
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| MS Ion Source- Electrospray Ionization |
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| Used with HPLC Carrier gas Droplets have a positive charges and accelerated across gap with potential |
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| MS Ion Source- MALDI |
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| Matrix Assisted Laser Desorption Ionization Used for large molecules Pulse with photons of laser energy to blast off chunks Ions streamed through TOF analyzer |
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| Mass Analyzer- Quadrapole |
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| Most common in forensics Poles paired with fixed voltage or alternating current in radio frequency Ions spirals down length of tube Ions with specific mass can only make it down |
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| Mass Analyzer- Ion Trap |
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| Also frequently used Ions oscillate inside- only right size will pass through Alternating current |
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| Mass Analyzer- Ion Cyclotron Resonance |
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| FT-ICR |
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| Mass Analyzer- Time of Flight (TOF) |
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| Often used with MALDI Energy potential becomes the source Light ions move faster Time it takes is proportional to mass Can determine mass of ion up to 3 decimal places |
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| Mass Analyzer- Ion Mobility Spectrometer |
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| Electrodes accelerate ions Similar to time of flight Used as portable "sniffer" for drugs, explosives, and chemical warfare agents |
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| Mass Analyzer- Tandem MS/MS |
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| 3 quadrapoles Used with liquid chromatography to screen tox samples |
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| Total Ion Chromatogram (TIC) |
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| Sum of intensities of all ion fragments |
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| Extracted Ion Chromatogram (EIC) |
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| Generally "post run" process Can go back until you find what you want Sum of selected ions from each scan Reconstructed Ion Chromatogram Fire debris analysis |
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| Single/Selective Ion Monitoring (SIM) |
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| Only a few specific ions scanned More sensitive than normal scan More data collection time at each ion Toxicology- at of drug in bodily fluids is small "Pre-run": set up prior to scan, extracts only selected ions Can't go back |
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| Calibration of MS |
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| Mass calibration done weekly with perfluorinated cmpds |
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| "Tuning the MS" |
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| Adjustment of ionization, repeller, and accelerator voltages Most MSD have "auto-tune" |
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| Fire Debris Extraction Techniques |
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| Steam Distillation Simple Headspace Headspace Concentration- Passive (ASTM E1412 Activated Charcoal), Dynamic, SPME (Solid Phase Microextraction) Solvent Extraction |
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| Instrumentation- Analysis of Ignitable Liquids |
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| GC with FID, GC-MS |
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| Ignitable Liquid Classifications |
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| ASTM E1618-06 8 classes with 3 potential subclasses for each |
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| Gasoline Recognition |
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| Blended Product C4-C12 with alkanes, aromatics, cycloparaffins Aromatics most abundant group Xylnes, C3 Castle, C4 Gang of four |
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| EIC Chromatogram Plots- Fire Debris |
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| Alkanes Cycloalkanes Aromatics Napthenics Indanes |
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| Fire Debris Analysis- Class determinations |
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| [image] |
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| Spot Tests |
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| [image] |
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| Scott Test |
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| Cocaine salts/Base reagent= positive result requires all 3 |
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| Mandelin Test |
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| Green for amphetamine and methamphetamine |
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| Confirmation Tests for Drugs- Categories of Analytical Techniques |
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| 1 A and 1 B 2 Bs and 1 C [image] |
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| HPLC vs. GC |
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| More suitable for thermally unstable cmpds- explosives Samples must be particulate free |
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| HPLC Injector |
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| Precise volume 6 port loop injector often used Fixed volume most reproducible |
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| HPLC Normal Phase |
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| Non-polar mobile phase with polar stationary phase |
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| HPLC Reverse Phase |
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| More polar mobile phase with stationary phase Most commonly used |
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| HPLC Isocratic Solvent Selection |
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| One solvent mixture throughout entire analysis Simple mixtures or polymer analysis |
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| HPLC Gradient Elution |
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| Changing from one solvent mixture to another over time during the run Analogous to temperature programming in GC Enhances separation of early eluting components while reducing elution time for later components |
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| HPLC UV/Visible Absorption Detectors |
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| Fixed wavelength Variable wavelength Diode array detection (multiwavelength) |
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| Diode Array Detector |
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| Multiwavelength Needs to absorb in UV or visible range Lots of double bonds, aromatic character Cmpds with saturated hydrocarbons don't work (fire debris) Light absorbed and then split into specific wavelengths |
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| HPLC Fluorescence Detector |
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| More sensitive than absorbance detectors Cmpd must fluoresce Used for LSD |
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| HPLC Infrared Absorption Detector |
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| Solvent interference restricts widespread application |
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| HPLC Refractive Index Detector (RI) |
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| Least sensitive Best for non UV absorbers (sugars) Not suitable for gradient elution Reference side and sample size |
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| HPLC Mass Spectrometry Detector |
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| Becoming 2nd most common Very sensitive Solvent removal Allows for better identification of peak |
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| HPLC Forensic Applications |
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| Drug tox- polar cmpds, metabolites, enantiomeric separation Explosives- thermally unstable, good UV absorbers Questioned documents- analysis of inks, dyes Polymer analysis- size exclusion chromatography, fibers, plastics, adhesives |
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| UV/Vis Spectroscopy Cmpd Classes |
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| Aromatic compounds- controlled substances, metabolites, organic dyes and pigments, some explosives Nitro compounds Transition metal compounds |
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| IR Detector- Deuterated Triglycine Sulfate (DTGS) |
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| Most widely used detector in IR Wide sensitivity range and quick response Photoelectric transducer |
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| IR Detector- Mercury/Cadmium Telluride (MCT) |
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| Photoconducting transducer Narrower sensitivity range, but more sensitive Needs liquid nitrogen cooling to reduce thermal noise |
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| IR Diffuse Reflectance |
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| Rough surface scatters light in all directions Sample mixed with non-absorbing material (non-compressed KBr) or on surface of silica carbide paper |
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| IR Attenuated Total Reflectance |
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| Internal Reflectance- ATR commonly used Good for opaque or other hard to hand samples (pastes, adhesives) Doesn't require any big prep work |
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| IR Forensic Applications |
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| Controlled substances (crack cocaine vs. cocaine salt) Automobile make, model, year from paint fragments Polymers (fiber analysis, tapes, adhesives) Infrared microscope- trace analysis, fibers, paint |
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| IR Frequency Table |
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| [image] |
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| Raman with FTIR Sampling |
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| Aqueous solutions and glass sample containers can be used Minimal sample prep |
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| Raman with FTIR- Fluorescence |
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| Much greater than Raman intensity Broad background with superimposed Raman spectrum (hill with grass on top) "Photobleaching" sometimes effective |
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| Raman with FTIR- Laser Power |
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| Must be adjusted to prevent burning of trace sample- especially dark colored materials (black tar heroin, smokeless powder) |
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| Raman with FTIR Forensic Applications |
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| Seized drug analysis Scan through baggies, glass vials Minimal sample prep Portable units available to take to clandestine lab scenes Explosives analysis Paints Fibers and other polymers Inks |
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| Paint Layers |
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| Clearcoat Effect coat Basecoat Surfacer Electrocoat Primer |
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| Analysis Methods of Paint |
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| Solubility Pyrolysis GC FTIR Microscopy |
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| TLC Normal Phase |
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| Polar silica stationary phase, relatively non-polar mobile phase |
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| TLC UV Fluorescence |
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| Most common 254 nm and 365 nm Analyte absorbs UV- dark spot, bright bkd No bkg fluorescence with 365 nm, but analyte may fluoresce |
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| TLC Universal Reagents |
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| Iodine vapor (double bonds)- reversible Conc. sulfuric acid w/heating |
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| TLC Group Specific Reagents |
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| Ninhydrin- amine groups Iodoplatinate- drugs Fast blue B- cannabinoids Ehrlich- LSD Diphenylcarbizone/HgSO4- barbiturates |
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| TLC Forensic Applications |
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| Drug screening Ink analysis Explosives screening |
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| Ink Analysis Forensic Applications |
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| Counterfeit currency Authentication of historical documents Written materials relative to another crime Ink stain comparison |
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| Document Accelerated Aging Approaches |
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| UV Accelerated Aging- dye partially degraded, solvent still present Thermal Accelerated Aging- solvent gone, dye intact |
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| Age Dating Inks Analysis |
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| Dye composition changes: HPLC-DAD and laser desorption MS Changes in ink solubility with time Solvent changes (evaporation) Changes in dye composition |
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| High Explosives |
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| TNT PETN ANFO Nitroglycerin HMX |
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| Low Explosives |
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| Smokeless Powders Black Powder (Pyrodex) Pyrotechniques |
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| Smokeless Powder Shapes |
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| Ball Disk Rod or tube Characteristic of manufacturer and brand |
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| Explosive Analysis (Post Blast) |
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| GC/MS primary HPLC and CE SEC TLC |
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| Explosive Device Detection (Pre Blast) |
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| Ion mobility spectroscopy (IMS) Canine X-ray imaging |
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| Metals Analysis- Flame Atomic Absorption |
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| Single element analysis Least sensitive method Best for alkali metals (Li, Na, K) |
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| Metals Analysis- Graphite Furnace AA Electrothermal or Flameless AA |
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| Single element Good to ppb levels for some metals Very small amts of sample |
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| Metals Analysis- Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) |
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| Simultaneous elements Good to sub ppb levels (most sensitive) |
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| Metals Analysis- X-Ray Fluorescence |
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| Very little sample prep |
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| Metals Analysis- ICP-MS |
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| Best for toxicology Simultaneous multi-element method Very sensitive Capable of isotopic composition of element |
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| Metals Analysis- Neutron Activation Analysis (NAA) |
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| Little or no pretreatment Needs nuclear reactor as source of neutrons Non-routine analysis Specialized |
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| Metals Analysis Forensic Applications |
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| Bullet lead comparison GSR Explosives Trace elements in glass (Laser Ablation ICP-MS) Metallic poisons |
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| NIDA-10 Drugs (*NIDA-5 Drugs) |
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| Amphetamines* Barbiturates Benzodiazapines Cannabinoids* Cocaine* LSD Methadone Opiates* Phencyclidine(PCP)* Propoxyphene |
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| Strongly Acidic Drugs |
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| Salicylic acid Pheylbutazone 2,4-Dinitrophenol |
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| Weakly Acidic Drugs |
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| Acetominophen Phenobarbital Chlorothiazide |
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| Amphoteric Basic Drugs |
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| Morphine Gabapentin Benzoylecgonine |
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| Strongly Basic Drugs |
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| Amphetamine Chlorcyclizine |
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| Plasma |
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| Whole blood centrifuged to remove cellular material, clotting factors still present |
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| Serum |
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| Similar to plasma but does not have clotting factors |
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| Denaturation of Proteins |
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| Elevated temperature pH Organic solvents Enzymatic breakdown of protein or conjugate |
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| Tox GCMS Internal Standard |
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| Deuterated drug or metabolite is best |
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| Tox GCMS Confirmation |
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| SIM usually required for sensitivity Target ion plus at least 2 confirmatory ions |
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| Tox LCMS/MS |
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| Becoming preferred method Minimal sample prep |
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| Tox Fractionation Scheme |
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| [image] |
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| Salt vs. Free Base IR |
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| OH band generally broader and more absorbing than free base |
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| Fingerprint Region in IR Spectrum |
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| Below 1200 cm-1 |
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| Band found at 2350 cm-1 in a background KBr pellet |
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| Carbon dioxide in the atmosphere |
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| Primary and Secondary Explosives |
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| Primary- shock sensitive Secondary- requires detonator |
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| Vibrational Spectroscopies- Raman vs. IR |
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| Raman spectrum- inelastic scattering IR- absorbance of light photons |
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| BAC Analyzed By: |
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| Headspace sample GC with FID N-Proponal as IS |
