Applications of capillary electrophoresis in forensic analytical chemistry

1. Jace James & Lauren Erland Applications of capillary electrophoresis in forensic analytical chemistry

2. Capillary Electrophoresis (CE) • Separation based on charge & frictional force

3. CE • Capillary zone electrophoresis (CZE) • Separation of charged molecules based on electrophoretic mobilities & migration velocities • Detection INORGANIC compounds • Micellar electrokinetic chromatography (MEKC) • Combines electrophoresis and chromatography • Simultaneous separation of neutral and charged molecules • Detection ORGANIC compounds • Microchip CE • Portable • Presence explosive-compound residues

4. Detection of Separated Compounds • CE can be coupled with diverse detection devices depending on the analyte of interest • UV-Vis • Laser induced fluorescence (LIF) • Electrospray Ionization (ESI) • Allows coupling with MS • NMR • Chemiluminescence

5. Advantages • Simple instrumentation • Exceptional power & resolution • Rapid analysis time • Highly versatile • Same instrument, often same capillary can be used to run diverse samples (change only running buffer) • Can be coupled with many different detection devices • Separation of charged, neutral and volatile molecules • Low mass limits of detection • Nanograms or picograms of sample • Minimal damage to sample • Inexpensive reagents • Waste is mostly aqueous, environmentally friendly • Minimal sample requirements • Direct sample injection • In many cases no sample prep required

6. Gunshot Residue (GSR) & Explosives • Produced when a firearm is discharged • Deposited on hands of the perpetrator • Components include: • Unburned powder • Heavy metals from the barrel of the gun, primer and cartridge • Determination if firearm has been fired • identify bullet holes • estimate firing distance • Detection military, industrial and home-made explosives

8. Current Methods for Detection • Most common: Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM-EDX) • moderate sensitivity, requires expensive instrumentation, is highly demanding in terms of professional skills, and is a very time consuming process. • Identification INORGANIC compounds ONLY • Push towards ORGANIC primers • False Negatives!!!

9. SEM-EDX: A case study • 2001 • Identification of a single, partially burnt gunpowder grain on a suspect’s clothing • SEM unsuccessful • CE was able to identify and individualize the gunpowder grain • MEKC can be used to detect ORGANIC compounds • CZE for INORGANIC compounds

11. Ink Analysis • Separation is a vital step in ink analysis • Ink components vary widely with manufacturer, colour • Possibility of contamination from writing surface • Chemical changes as ink ages • Results can be stored electronically • Development reference libraries • Difficult to find a single method for separation of such diverse mixtures

13. Current Techniques • TLC • Low resolution • Low power of differentiation • GC & HPLC commonly used • Greater technical skill required • Large sample size • Costly • Extensive sample prep • Difficult for complex samples • Destructive • Time consuming

14. CE & Ink Analysis • CE appropriate for many different types of analyte • Organic, inorganic, volatile • Need only change running buffer • Quick, easy and inexpensive! • Extraordinarily small quantities required • Pico or nanoliters • Virtually non-destructive • Detection generally by UV-Vis • Has been applied to many types of pens and inks • Fountain-pen, ballpoint, water-soluble, red, blue and black inks

15. CE readily differentiates inks originating from different manufacturers Reproducible migration times and relative peak areas

16. Capillary Electrophoresis • Simple • Low Cost • Short analysis time • Non-destructive • High power resolution and separation • Potential to expand to many other applications • Eco-Friendly!