Term
|
Definition
| Source --> Degassing System--> Pump --> Injector --> Thermostated Column --> Detector |
|
|
Term
|
Definition
-HPLC
-gas is compressed at the beginning and decompressed at the end and this caused bubbles to form which make the column less efficient
-He gas is used because it doesn't dissolve, it picks up the gases and is swept away |
|
|
Term
| Low Pressure Gradient Pump |
|
Definition
-mixing chamber is located on the low pressure side of the pump
-solvent A and B are mixed in chamber and then proceed to the pump |
|
|
Term
| High Pressure Gradient Pump |
|
Definition
-HPLC
-mixing chamber is located on the high pressure side of the pump
-solvent A and B go through their own pumps and then go to the mixing chamber |
|
|
Term
|
Definition
-one solvent mixture throughout entire analysis
-used for simple mixture or polymer analysis
-no equilibration time needed between runs |
|
|
Term
|
Definition
-HPLC
-changing from one solvent to another mixture over time
-enhances separation of early eluting components while reducing elution time for later compounds |
|
|
Term
|
Definition
-~ 60,000 psi
-~ 1mL/min
-sapphire, special alloys and Teflon are usually used |
|
|
Term
|
Definition
~ 20,000 psi
less than 1 mL/min
-utilizes A and B piston system (A is larger than B)
- pistons move in and out, as A withdraws and pulls in solvent, B goes out and pushes solvent through |
|
|
Term
|
Definition
-fixed volume is more reproducible
- can do variable volume by partial filling
-load sample then rotate 60 degrees to connect with mobile phase which pushes it through
-need to keep length short to avoid diffusion and broadening |
|
|
Term
|
Definition
Normal: polar stat phase and non polar mobile phase
-silica gel
Reverse: nonpolar stat phase (C8 or C18) and polar mobile phase (usually water)
-bonded silica (hydrocarbons chemically bonded) |
|
|
Term
| Spectrophotometric Detector (HPLC) |
|
Definition
-UV/Vis absorption commonly done at 254 nm
-Mercury vapor lamp used
-good for aromatics and conjugated molecules |
|
|
Term
| Diode Array Detection (HPLC) |
|
Definition
-illuminate entire sample with broad spectrum of light and then measure light absorbed, then split into wavelengths and measure with diode array
-good for smokeless powders
-separation = window/# of diodes |
|
|
Term
| Fluorescence Detector (HPLC) |
|
Definition
-monitor emission and excitation wavelengths
-more sensitive than absorbance detectors (only for fluorescent compounds)
-good for LSD |
|
|
Term
|
Definition
| Spectrophotometric, Diode Array, Fluorescence, IR, Refractive Index, MS |
|
|
Term
| Refractive Index Detection (HPLC) |
|
Definition
-one of the oldest detectors, least sensitive
-as light passes through it is bent because of a change in the RI between the sample and the reference cell
-negative peaks occur when the RI of an analyte is lower than the mobile phase and positive occurs when it is higher
-not suitable with gradient elution because the RI of mobile phase changes
-Source--> Flow Cell-->Optical Compensator-->detector-->feedback control device |
|
|
Term
|
Definition
-solvent removal is biggest problem
-currently more expensive than others
-allows for better identification
-LCMS becoming standard for Tox |
|
|
Term
| HPLC Advantages and Disadvantages |
|
Definition
-more suitable for thermally unstable compounds and non-volatiles.
-Generally non destructive
Disadv: potentially dangerous solvents are used, more expensive interfacing to MS, samples must be particulate free and MUST be soluble |
|
|
Term
|
Definition
-thermally unstable compounds (explosives)
-non-volatiles
-Tox screening
-Dyes, inks, QD
-Polymer analysis, fibers, plastics
-drugs and drug metabolites |
|
|
Term
| Efficiency and Reproducibility of HPLC* |
|
Definition
-commercial columns have consistent particle size allowing for reproducibility even when switching columns
-fixed volume sample loop is very reproducible |
|
|
Term
|
Definition
-uses a diffraction grating like UV-Vis spec
-moving the angle of grating "scans" the wavelength across a single detector (takes 10-20 mins)
-uses a slit to affect the resolution and to isolate a particular wavlength
-earliest IR instruments had this type |
|
|
Term
|
Definition
-4000-400 cm-1
-increase wavelength = increase energy
-Abs=-logT |
|
|
Term
|
Definition
-uses an interferometer to collect the whole spectrum at once
-beam splitter separates original beam into 2 halves, one goes to fixed mirror, the other to the moving mirror
-ion source produces an abundance of IR energy over a broad range when heated electronically
-the moving mirror vibrates in and out of a # of cycles per second and the distance to the beam splitter changes
- changes the pathlength
-Helium laser is used as a position finder for the moving mirror
-Detector measures the variation in the intensity with time |
|
|
Term
|
Definition
-FTIR
-dispersive has a limited throughput because of the required slits which must be moved close together for resolution but FT has a much larger area of sampling because it has no slits |
|
|
Term
|
Definition
-the noise of the spectrum is detector limited but when the entire spectrum is spread over an entire spectrum, therefore the signal to noise ratio is much better
-noise is a random function and is sometimes higher and sometimes lower, by combining scans you will decrease the noise and improve the signal |
|
|
Term
|
Definition
-dependent on the number of points per scan and is a function of time
-increasing the number of points increases the resolution across the top of the peak, but you don't want to make more points than necessary |
|
|
Term
|
Definition
| Deuterated Triglycine Sulfate (TGS), Mercury/Cadmum Telluride (MCT) |
|
|
Term
|
Definition
| Deuterated Triglycine Sulfate (TGS), Mercury/Cadmum Telluride (MCT) |
|
|
Term
| Deuterated Triglycine Sulfate Detector (DTGS) |
|
Definition
-FTIR
-photoelectric transducer with a wide sensitivity range and quick response
-1-40 micrometers with gap in the middle
-standard and most widely used |
|
|
Term
| Mercury/Cadmium Telluride Detector (MCT) |
|
Definition
| -FTIR -photoconducting transducer -narrow sensitivity range but MORE sensitive than DTGS -1-6.5 micrometers -needs liquid nitrogen cooling (77K) to reduce thermal noise -motion of electrons is enough to cause this -common with IR microscope and GCIR -need a high sensitivity because very little light is hitting the detector -uses a semiconductor |
|
|
Term
|
Definition
-gases are contained in a gas cell with a long path length
-need a long path length to get adequate absorption, at least 10 cm
-can use mirrored cells or open path systems (source is at one end and detector is at another end of the room) |
|
|
Term
|
Definition
-droplet is compressed between 2 NaCl or KBr discs without spacers to create film
-you want a short path length (10s of microns)
-most liquids are highly absorbing in IR region
-fixed and variable path length cells
-salt windows are sensitive to water and alcohols (can use AgCl) |
|
|
Term
|
Definition
-NaCl= 40,000 to 600
-KBr = 43,500 to 400
-KCl = 33,000 to 400 |
|
|
Term
|
Definition
-pellets are used if can't dissolve solid
-alkali metal halide salts form glass like pellets under pressure
-finely ground solid is suspended in KBr pellet
- 1-2% by wt in KBr
- 1-5 mg of sample is needed
-pellet is 1 mm thick by 7-13 mm diameter |
|
|
Term
|
Definition
| Thin Films, Specular Reflectance, Diffuse Reflectance, Attenuated Total Reflectance, KBr Pellet |
|
|
Term
|
Definition
-FTIR
-useful for determining composition of plastic films or thin sheets and are mounted directly on the beam
-solution of material is placed on a salt plate, solvent evaporates leaving a thin film |
|
|
Term
|
Definition
-FTIR
-non destructive
-IR beam is reflected off a shiny surface of the sample and you measure the reflectance
-good for crystals or thicker, smooth plastic
-beam penetrates slightly into the sample and you get absorbance
-requires Kramer-Kronig transformation |
|
|
Term
|
Definition
-FTIR
-time consuming, not used often
-rough surface scatters light in all directions and is compared to just KBr
-intensity of the reflection is related to the molar absorptivity
-sample is mixed with a non-absorbing material (~5% in KCl) on surface of silica carbide paper
-requires Kubelka-Munk transform (intensities vary)
-good for drugs and paint |
|
|
Term
| Attenuated Total Reflectance (ATR) |
|
Definition
-FTIR
-beam goes from higher RI to lower RI and you want it to strike the IRE at an angle to insure total reflectance
-total reflection occurs beyond the critical angle (no penetration occurs with the material)
-evanescent wave penetrates the material a wee bit
-a succession of several total but attenuated reflections is done
-depth of penetration increases with the wavelength |
|
|
Term
| Forensic Applications of FTIR |
|
Definition
-identification of controlled substances
-ID of auto make, model, year from paint fragments
-ID of polymers |
|
|
Term
|
Definition
| A rapid build up of heat and gases that results in a violent disruption of the surrounding environment |
|
|
Term
|
Definition
a rapid combustion that moves through an explosive material at a velocity less than the speed of sound (<1000 m/s)
-low explosives |
|
|
Term
|
Definition
a reaction that moves through an explosive material at a velocity greater than the speed of sound (>1000 m/s)
-high explosives |
|
|
Term
|
Definition
Low Order: an incomplete reaction of the explosive material (due to air pockets, wrong type of initiator, deterioration over time, poor contact, or inadequate containment of low explosive)
High Order: a complete reaction of the explosive material |
|
|
Term
|
Definition
Explosive Mixture: a mechanical blending of an oxidizer and a fuel to produce a mixture that can produce an explosion
-usually low explosives (except for ANFO)
Explosive Compound: a chemical compound whose molecules can produce an explosion without the addition of a fuel or oxidizer
-TNT, NG
-oxidizer and fuel are chemical bonded together |
|
|
Term
|
Definition
-must be contained
-deflagrate
-Smokeless powder, black powder, pyrotechniques |
|
|
Term
|
Definition
-low explosive
-used in ammunition, pistols, rifles, shotguns
-Single base: NC
-Double base: NC+NG
-Triple base: NC+NG+ nitroguanidine/TNT
-used for battleships
-diphenylamine is a stabilizer used becuase NC loses nitro groups over time and it scavenges them |
|
|
Term
|
Definition
ball- like pringles
Disk-may or may not be perforated
Rod or Tube
Lamelli=flat cut shape (trapezoidal)
T-shaped-new |
|
|
Term
|
Definition
-low explosive
-charcoal + KNO3 + sulfur
-pyrodex has chlorate instead of S
-muzzle loaders and fireworks
-hasn't changed much since middle ages |
|
|
Term
|
Definition
-mainly black powder with various metal salts and metal powders for color and effect
-may contain flash powder |
|
|
Term
|
Definition
detonate
primary, secondary, or tertiary |
|
|
Term
|
Definition
| -do not require a detonator -friction sensitive, shock sensitive, temperature sensitive -NG, EGDN, HMTP, TATP, Azides, fulminates, pulcrites, DDPN |
|
|
Term
|
Definition
-primary explosive
-6500 m/s
-used in dynamite, double based smokeless powders, and some military formulations
-modern ones might have EGDN-less sensitive
-can seep out of old TNT and that is bad
-cold crystals of NG can rub together and that's enough to go off |
|
|
Term
|
Definition
-ethylene glycol dinitrate
-primary explosive, high |
|
|
Term
|
Definition
| -hexamethylene triperoxideamine -primary explosive, high -peroxide based -5100 m/s -extremely sensitive -popular with some extremist groups -found occassionally in meth labs |
|
|
Term
|
Definition
-Tetraacetone triperoxide
-primary explosive, high
-peroxide based
-easily made from things you buy at the store
-extremely sensitive |
|
|
Term
|
Definition
-high explosive
-booster charges
-requires energy from primaries
-commercial: TNT, Dynamite, PETN, Tovex
-military: RDX, HMX |
|
|
Term
|
Definition
-secondary explosive, high, commercial
-trinitrotoluene
-6500 m/s |
|
|
Term
|
Definition
-secondary, high, commercial
-mixture of NG, EDG, NC and/or TNT with sawdust or diatomaceous earth
-not shock sensitive, requires blasting cap
-components can be added to make it more stable |
|
|
Term
|
Definition
-secondary, high,
-pentaerythrite tetranitrate
-8300 m/s
-used in detonating cord and shaped charges
-commercial, but can be military |
|
|
Term
|
Definition
-secondary, high, military
-8360 m/s
-used in C4
-military |
|
|
Term
|
Definition
| -secondary, high, military |
|
|
Term
|
Definition
-high
-ammonium nitrate based
-requires energy from secondary and primary
-ANFO, water gels |
|
|
Term
|
Definition
-tertiary, high
-ammonium nitrate/ fuel oil
-commercial-used in mining operations with booster charges
-requires a blasting cap
-was used in OK city bombing
-AN fertilizer is readily available |
|
|
Term
|
Definition
-improvised explosive device
-a device placed or fabricated in an improvised manner incorporating destructive, lethal, noxious, bla bla bla
-contains a detonator or fusing mechanism, a timer, remote, trigger, arming mechanism, explosive, containment, and concealment
-LOW: poor man's C4, flash mix, armstrong's mix, homemade black powder
-High: TATP, HMTD
-Pipe bombs |
|
|
Term
|
Definition
-low IED
-postassium chlorate and vaseline (90/10) |
|
|
Term
|
Definition
-low IED
-potassium chlorate and alluminum/sulfur |
|
|
Term
|
Definition
-low IED
-potassium chlorate and red phosphorus
-particularly nasty |
|
|
Term
|
Definition
-low IED
-charcoal, S and KNO3
-grains of S and charcoal (From wood) indicate homemade |
|
|
Term
|
Definition
-IED
-0.75 to 1 in diamter and 6-8 in long
-can glue metal on outside for shrapnel
-needs an initiation device like an electrical match or a blasting cap
-simple to make, materials available |
|
|
Term
|
Definition
| the particular shape of the explosive with a Cu sheeting around it focuses the explosive downword |
|
|
Term
|
Definition
| blow air and lower the pressure so much that you get a partial vacuum that sucks lighter material back in |
|
|
Term
|
Definition
-in or near crater: explosion creates presure wave out leaving low pressure at site of explosion that pulls in light material
Away from crater: distance dependent on force of the explosion and obstruction and heavier debris is carried by force of explosion |
|
|
Term
|
Definition
1/2: GCMS, IR, EDX, XRD, LCMS
3: GC, LC, IC, CE
4: burn, flame, MP, Spot tests |
|
|
Term
| Post Blast Chemical Analysis |
|
Definition
-GC/MS primary
-HPLC and CE as alternative methods
-SEC for plastic fragments
-TLC still used sometimes for screening for SB and DB powders |
|
|
Term
| Pre-Blast Device Detection |
|
Definition
-IMS detection of vapors from explosives
-canines (NC, black powder, ANFO)
-X-ray |
|
|
Term
|
Definition
Marking Agents: semi-volatile materials added to less volatile high explosives
-DMNB added to C4
-not really taggants
Identification Tags: taggents, small color-coded particles added to high explosives which will survive blast
-identify manufacturer |
|
|
Term
| Forensic Applications of ink analysis |
|
Definition
-detection of counterfeit currency
-authentication of historical documents
-written materials relative to another crime
-ink stain comparison |
|
|
Term
| Carbon Based Ink/India Ink |
|
Definition
-some of oldest known
-used by ancient chinese
-mixture of carbon black and glue made into cakes (made from soot from candles)
-cake is ground with water to make a suspension
-today shellac and borax are used with wetting agents instead of glue
-waterproof
-used in drawing and printing ink and fine art prints |
|
|
Term
|
Definition
Iron Gallo-tannates: made from Fe salts and gallo-tannic acid from tree galls
- iron salts tend to be acidic and can destroy paper when exposed to enough moisture in the air
-declaration of independence and constitution
- initially nearly colorless and exposure to air turns it brown-black
- modern inks contain synthetic dyes
synthetic dyes in aq. solutions: brilliant colors but not as stable as blue-black |
|
|
Term
|
Definition
-most frequently used instrument for writing
-ink is a viscous mixture of synthetic dyes in various solvents (many are proprietary)
-dyes: crystal violet, methyl violet, tetramethyl para rosaniline, and victoria blue
-solvents: glycols and glycerin, benzyl alcohol |
|
|
Term
|
Definition
-more similar to marker ink than ballpoint
-similar inks to those used in textile industry
-not water fast
-less dye than BP, more than fountain |
|
|
Term
|
Definition
| India/Carbon, Fountain (Iron Gallotannate and Synthetic), Ballpoint, Rolling Ball, Fiber Tip, Gel |
|
|
Term
|
Definition
-inks contain dyes and additives similar to fluid inks
-water based or xylene based (water resistant and permanent)
-metal chelated dyes are relatively light fast (Cu thiocyanate) |
|
|
Term
|
Definition
-water based, pigmented gel ink
-black and colored pigments rather than dyes
-special pigments, resin and additives to give high static viscosity
-thixotrpic (formulated to become thinner when used)
-easily recognized by TLC
-made for space! |
|
|
Term
| Spectroscopic Techniques (Inks) |
|
Definition
-illumination with UV-IR
-visual comparator gives fluorescence
-microspectrophotometer
-color and brightness of fluoresence
-PIXE and Xray for metal content of pigments or dyes
-micro-FTIR: can take reflectance spectra through microscope of an individual line and compare it to other parts of the check
-difficult to remove contribution of paper components because of its heterogeneous nature
-diffuse FTIR of ink extracts |
|
|
Term
| Chromatographic Tehcniques (Inks) |
|
Definition
| TLC, Spectral Reflectance, Micro Punch |
|
|
Term
|
Definition
-most commonly used
-small sample size, quick screening
-micro-plugs taken with blunt hypodermic needle
-extract with pyridine (BP), or ethanol-water(others)
-can look at Rf, color, fluorescence for differentiation
-can show different amounts of different components |
|
|
Term
| Spectral Reflectance of Inks |
|
Definition
-chromatographic technique
-measurement of reflectance at various wavlengths can be used to compute the RGB profile
-used in paint matching devices at paint stores |
|
|
Term
|
Definition
-used for sampling documents
-punch tiny plugs out of paper and then push them all out into a microcentrifuge tube to do extaction |
|
|
Term
|
Definition
-look at solvent changes, solvent evaporates over time
-Dye changes: strong bonding of dye and paper fiber occurs over time and it becomes less soluble |
|
|
Term
| C-H, Aromatic C-H, O-H, amine, CdoubleO, nitrile, CdoubleC, C-C |
|
Definition
CH alkane: 3000-3850
CH alkene 3100-3000
CH aromatic: 3150-3050
C-C alkane: not useful
CdoubleC, alkene: 1680-1600
CdoubleO aldehyde: 1740-1720
ketone: 1725-1705
COOH: 1725-1700
Ester: 1750-1730
Amide: 1680-1630
O-H: free 3650-3600
h-bonded 3400-3200
N-H, amine: 3500-3100
C-N, amines 1350-1000
CtripN, nitrile 2260-2240 |
|
|
Term
|
Definition
-physical: fluorescence quenching, fluorescence, absorbance, optomechanical scanning, electronic scanning
-Microchemical Detection: pre and post chromatographic derivitization, universal and specific spray reagents
-Microbiological detection; bioautography |
|
|
Term
| Fluorescence Detection of TLC |
|
Definition
-compounds that fluoresce absorb UV light and fluoresce back in the visible
-a number of dyes are fluorescent
-use mercury vapor lamp at UV source
-254 for quench and 365 for fluoresce
-quenching: analyte absorbs UV leaving a dark spot behind behind on a light background |
|
|
Term
| Chemical Visualization Spray Reagents |
|
Definition
Universal: Iodine vapor, concentrated sulfuric acid
Specific: ninhydrin, iodoplatinate, fast blue b, erlich, diphenylcarbizone |
|
|
Term
| Iodine Vapor Visualization of TLC |
|
Definition
-universal spray reagent
-must have double bonds
-gives brown spots
-often reversible |
|
|
Term
| Concentrated Sulfuric Acid Visualization |
|
Definition
-universal reagent
-brown-black
-messy, dangerous, no other tests possible, chars the plate
-always last one done
-requires heat |
|
|
Term
|
Definition
-group specific, amines
-blue
-often 1st spray done
-many drugs, drug metabolites |
|
|
Term
| Iodoplatinate Visualization |
|
Definition
-various colors
-many drugs, particularly opiates |
|
|
Term
| Fast Blue B Visualization |
|
Definition
group specific TLC Spray Reagent
cannibinoids |
|
|
Term
| Erlich's Reagent Visualization |
|
Definition
|
|
Term
| Diphenylcarbizone Visualization |
|
Definition
|
|
Term
|
Definition
-fluorescence intensity
-UV/Vis absorbance with densitometer
-Diffuse reflectance (silica is good diffuse surface)
-laser desorption |
|
|
Term
|
Definition
-used with limited amount of material
-scrape off and elute with appropriate solvent
-do UV/Vis, GCMS, HPLC |
|
|
Term
| Forensic Applications of TLC |
|
Definition
-drug screening, Tox,
-ink analysis, QD
-Explosives |
|
|
Term
|
Definition
| the total residues resulting from the discharge of a firearm, it includes both gunpowder and primer residues, plus metallic residues from projectiles, fouling |
|
|
Term
|
Definition
| -a particle composed of PbBaSb fused together in a single unit, which exhibits the correct morphology |
|
|
Term
|
Definition
| -when the weapon is discharged, products of combustion, unburned powder and particles from primer are discharged fromt he muzzle, breach and other openings |
|
|
Term
|
Definition
-inidcates possible firing of weapon recently
-can infer distance from shooter to target |
|
|
Term
|
Definition
1) confirm nitrite sensitivity of test paper using a nitrite test swab saturated with 15% acetic acid solution and dab at corners
2) mark reference points of evidence on test paper by placing evidence face down on emulsion coated side of test paper and marking seams, buttons, etc with paper
3) create layers of reaction items by soaking cheesecloth in acetic acid, ringing, placing on top of evidence on top of photosensitive paper
4) heat reaction layers with an iron and acetic acid steam is forced through the layers causing the color-producing reaction
5) examine and interpret results, discard the cheesecloth and separate evidence from test paper, any orange on the paper are a result of the reaction
6) distance determination by comparing pattern from victim vs. test shots at standard distances
contact, 3, 6, 9, 12, 18, 24 |
|
|
Term
|
Definition
| Sodium Rhodizonate, Dithiooxamide Test, Primer GSR ID |
|
|
Term
|
Definition
-GSR
-test for lead with the evidence revolver
-blue violet is positive
-can be used to detect bullet wipe |
|
|
Term
|
Definition
-GSR
-for Cu (green), Ni (blue/pink), and acetone extracts (blue)
-performed after Griess |
|
|
Term
|
Definition
-usually performed using SEM/EDX
-use a tape lift or sticky stubs to pick up particles |
|
|
Term
|
Definition
| a suspension of pigment in a film former (also called a vehicle) |
|
|
Term
|
Definition
-usually organic polymers with the purpose of protecting the surface and holding the pigments
-Varnish: commonly polyurethane dissolved in solvent which normally doesn't contain a stain, protects
-Stain: mix of organic dyes dissolved in solvent, made to penetrate wood and stain, not protect
-Enamel: a glossy, thermosetting paint but now any paint which dries glossy, solvent based, requires heat to complete |
|
|
Term
| Solvent Drying Mechanisms |
|
Definition
-Solvent Evap: used for rust proof paints (rustoleum and varnish)
-Heating/Thermosetting: chemical reaction is accelerated, used for automotives
-Oxidation: double bonds react with oxygen in air and you get a large 3D polymer |
|
|
Term
|
Definition
-Acrylic Lacquers: long chain, few crosslinking, soften when heated, used for GM topcoats
-Acrylic Enamels: polymer that crosslinks extensively when heated, hard surface and resistant to attack by solvents, freq with cars
-Alkyd Enamels: also extensively crosslinked when heated, used on imported cars
-Alkyd Resins: drying vegetable oils (linseed), air oxidation=crosslinking
-Polyurethane Resins: condensation polymer of isocyanates + activated alcohol compounds, used for floor coatings, resistant to water/alcohol
-Vinyl resins: vinyl chlorate or vinyl acetate, common house paint |
|
|
Term
|
Definition
| pieces of paint have come off surface and usually contain layers |
|
|
Term
|
Definition
| the top layer of paint, which has loosened due to being wet or air oxidation, smears onto another surface after brushing contact, layer structure not present |
|
|
Term
| General Analysis of Paint |
|
Definition
-color layer analysis
-same number/order of layers
-relative thickness
-additives |
|
|
Term
|
Definition
-1st layer
-coats metal and helps prevent rust and provides a good binding surface for the next layers on top of it |
|
|
Term
|
Definition
| -also a primer, provides a smooth surface for next layers |
|
|
Term
|
Definition
| -gives actual color to car, subject to fading with UV |
|
|
Term
|
Definition
| -metallic layer, clear binder with something suspended in it like mica to give metallic appearance |
|
|
Term
|
Definition
-protects lower layers and provides depth of color to car
-can be purchased locally |
|
|
Term
| Microchemical Test of Paint |
|
Definition
-solubility: in acetone, pyridine, dichloromethane
-Pyrolysis GC: anlaysis of film former
-FTIR: individual layers, primarily binders, some pigments |
|
|
Term
| Classes of Compounds of Forensic Interest (UV/Vis) |
|
Definition
-Aromatics: drugs/metabolites, explosives, organic dyes, amphetamines
-Nitro Compounds: TNT, DNT, nitroaromatics, NG, NC, generally below 210
-Transition Metals: inorganic dyes/pigments |
|
|
Term
| Parts of UV Spectrophotometer |
|
Definition
-Light source: combo of tungsten and deuterium lamps
-switch to tungsten at 350 for less background
-Monochrometer: quartz or fused silica, glass or plastic for visible
-Cuvette: responds to intensity of light |
|
|
Term
|
Definition
-slit allows only desired wavelength to go through and grating changes the light going through the exit slit
-filter cuts out stray light and focuses it
-typically measure the intensity of light as it goes through the reference and compare to the sample |
|
|
Term
|
Definition
Source-->Mono-->mirror 1--> sample or reference-->2nd mirror--->photomultipler-->detector
-uses a rotational mirror (aka chopper) to split beam to go to reference and sample and measures the ratio of the top to the bottom |
|
|
Term
| Photodiode Array (UV/Vis) |
|
Definition
-all light goes through the sample and then grating does the separation on to the diode
-computer reads the charge off of each diode which translates to the intensity of light
-as you widen slits, you allow more light from adjacent wavelengths which increases sensitivity but decreases selectivity |
|
|
Term
| Sources of Error for UV/Vis |
|
Definition
-round cuvettes don't have uniform pathlength
-any particles can scatter light in cuvette
-deviations at high and low (on calibration curve) due to light satter and self-absorbance |
|
|
Term
|
Definition
-point where both states have same absorptivity at some wavelength
-usually interested in total concentration of drug in sample and you use Iso point for this
can change pH and do series of measurements to find isobestic point |
|
|
