Separation based on charge & frictional force Capillary Electrophoresis (CE)
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
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
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
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
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!!!
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
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
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
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
CE readily differentiates inks originating from different manufacturers Reproducible migration times and relative peak areas
Capillary Electrophoresis Simple Low Cost Short analysis time Non-destructive High power resolution and separation Potential to expand to many other applications Eco-Friendly!