Forensic Chemistry & Toxicolog

Cheatsheet Content

### Presumptive Tests for Cocaine - **Most Common Test:** Scott test - **Scott Test Color Change:** Blue color - **Reagent for Scott Test:** Cobalt thiocyanate - **Reason for Blue Color in Scott Test:** Formation of cobalt-cocaine complex ### Presumptive Tests for Opiates - **Marquis Test with Opium/Morphine:** Purple/violet color - **Reagent for Marquis Test:** Formaldehyde + $\text{H}_2\text{SO}_4$ - **Mecke Test with Opiates:** Purple to blue-green color ### Presumptive Tests for Barbiturates - **Common Test:** Dille-Koppanyi test - **Dille-Koppanyi Test Color Change:** Red-violet color - **Dille-Koppanyi Reagent:** Cobalt acetate + isopropylamine ### Cannabis Information - **Plant Source:** *Cannabis sativa* - **Active Principles:** Cannabinoids ### Forensic Analysis Workflow 1. **Receipt of Suspected Sample** 2. **Proper Labelling, Sealing & Chain of Custody** 3. **Sample Preparation:** (Extraction / Digestion / Derivatization) 4. **Preliminary / Presumptive Tests:** (Colour tests, Spot tests, TLC screening) 5. **Selection of Confirmatory Technique:** (Based on nature of analyte) 6. **Instrumental Confirmatory Analysis** 7. **Comparison with Reference Standards:** (Retention time / Mass spectra / Absorption peaks) 8. **Data Interpretation & Validation:** (Qualitative identification $\pm$ Quantification) 9. **Result Confirmation:** (Meets legal & scientific acceptance criteria) 10. **Documentation & Report Writing** 11. **Expert Opinion & Court Presentation** ### Analytical Technique Selection #### Chromatography (Separation Technique) - Based on Distribution Between Two Phases - **Types:** - Paper Chromatography - TLC - Column Chromatography (AAS) - Gas Chromatography (GC) - High Performance Liquid Chromatography (HPLC) #### Spectroscopy (Identification Technique) - Based on Interaction with Energy / Radiation - **Types:** - UV-Visible - FTIR - Atomic Absorption - ICP-MS - Mass Spectrometry (MS) - NMR (advanced) ### UV-Visible Spectrophotometer - **Principle:** Absorption of UV/visible radiation causes electronic transitions in molecules (Beer-Lambert law). - **Method:** - Sample prepared in suitable solvent - Radiation passed through sample - Absorbance measured at specific wavelength - **Main Components:** - UV/Visible light source (Deuterium & Tungsten lamp) - Monochromator - Sample holder (cuvette) - Detector (photodiode) - Readout system - **Forensic Use:** Drug estimation, poison analysis ### FTIR (Fourier Transform Infrared Spectroscopy) - **Principle:** Molecules absorb IR radiation causing vibrational transitions characteristic of functional groups. - **Method:** - Sample prepared as KBr pellet / ATR - IR radiation passed through sample - Interferogram converted to spectrum using Fourier transform - **Main Components:** - IR source - Michelson interferometer - Sample compartment - Detector - Computer with spectral library - **Forensic Use:** Drug identification, polymers, fibers, explosives ### Thin Layer Chromatography (TLC) - **Principle:** Separation based on differential adsorption of components between stationary and mobile phases. - **Method:** - Sample spotted on TLC plate - Plate developed in solvent chamber - Spots visualized and Rf values calculated - **Main Components:** - Stationary phase (silica gel/alumina plate) - Mobile phase (solvent system) - Developing chamber - Visualization reagents - **Forensic Use:** Drug screening, poison comparison ### Gas Chromatography (GC) - **Principle:** Separation based on volatility and partitioning between stationary liquid phase and mobile gas phase. - **Method:** - Sample vaporized in injector - Carried by inert gas through column - Components separated and detected - **Main Components:** - Carrier gas (He, $\text{N}_2$) - Injector - Column - Detector (FID, ECD, NPD) - Data system - **Forensic Use:** Drugs, solvents, volatile poisons ### Gas Chromatography-Mass Spectrometry (GC-MS) - **Principle:** GC separates compounds; MS identifies them based on mass-to-charge (m/z) ratio after ionization. - **Method:** - GC separation - Electron impact ionization - Fragment ions analyzed by mass analyser - **Main Components:** - GC unit - Ion source - Mass analyzer (quadrupole) - Detector - Computer with NIST library - **Forensic Use:** Confirmatory test for NDPS drugs, poisons, explosives ### High Performance Liquid Chromatography (HPLC) - **Principle:** Separation based on differential interaction between solute, stationary phase, and liquid mobile phase. - **Method:** - Sample injected into high-pressure mobile phase - Separated in column - Detected using UV/FL detector - **Main Components:** - Solvent reservoir - Pump - Injector - Column - Detector - **Forensic Use:** Non-volatile drugs, toxins ### Atomic Absorption Spectroscopy (AAS) - **Principle:** Free atoms absorb radiation of specific wavelength characteristic of element. - **Method:** - Sample atomized in flame or graphite furnace - Absorption measured - **Main Components:** - Hollow cathode lamp - Atomizer (flame/furnace) - Monochromator - Detector - **Forensic Use:** Heavy metal poisoning (As, Pb, Hg) ### ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) - **Principle:** Plasma ionizes elements which are separated based on m/z ratio. - **Method:** - Sample nebulized into plasma - Ionization at high temperature - Mass analysis - **Main Components:** - Plasma torch - RF generator - Nebulizer - Mass analyzer - Detector - **Forensic Use:** Trace metal analysis, glass, hair, nails ### Instrument Selection for Specific Analytes - **Drugs of Abuse (NDPS):** GC-MS, FTIR, LC-MS/MS - **Pharmaceuticals:** HPLC, LC-MS/MS - **Volatile Poisons (cyanide, solvents):** GC, GC-MS - **Non-volatile Poisons:** HPLC, LC-MS/MS - **Arsenic, Lead, Mercury, Cadmium:** AAS, ICP-MS (trace and ultra-trace levels), ICP-OES (multi-element screening) - **Petroleum Accelerants:** GC-MS - **Organic Explosives (TNT, RDX):** GC-MS, HPLC - **Inorganic Explosives (nitrates, chlorates):** Ion Chromatography ### Instrument Selection for Biological Samples - **Blood & Urine:** GC-MS, LC-MS/MS - **Viscera:** GC-MS, HPLC - **Hair & Nails:** ICP-MS, GC-MS ### Instrument Selection for Physical Evidence - **Paint, Fibers, Polymers:** FTIR, Py-GC-MS - **Glass:** ICP-MS, SEM-EDS - **Unknown Powders:** FTIR, GC-MS ### Instrument Selection Criteria - Nature of evidence - Required sensitivity and specificity - Legal acceptability - Availability of reference standards ### Forensic Case-Based Mapping Examples - **Arsenic Poisoning:** Marsh test (screening) $\rightarrow$ AAS / ICP-MS (confirmatory) - **Heroin Seizure:** Color test $\rightarrow$ GC-MS confirmation - **Fire Debris:** GC-MS petroleum profile matching ### Comparison of Analytical Techniques in Forensics | Category | Non-Destructive Examples | Destructive Examples | Typical Forensic Use Cases | Why Preferred? | | :------------------- | :---------------------------------------- | :-------------------------- | :----------------------------------------- | :------------------------------ | | **Spectroscopy** | FTIR (ATR), Raman, Micro-XRF | GC-MS, LC-MS/MS, AAS | Drugs, paints, fibers, glass, inks | Preserve sample for re-test | | **Elemental** | SEM-EDS, Portable XRF | ICP-MS | GSR, glass, soil, metals | High specificity needed | | **Imaging/Microscopy** | Optical/comparison microscopes, VSC, ESDA | (Minimal; some mounting) | Documents, fibers, tool marks | Visual/non-invasive first | | **Chromatography** | (Rare; mostly non-destructive prelim) | GC-MS, LC-MS, TLC/HPLC | Drugs, arson, toxicology | Confirmatory power | | **Other** | Multispectral imaging, radiography | DNA extraction, chemical dissolution | Documents, biologicals | Evidence integrity |