Isolation, concentration and determination of post blast residua by
liquid chromatography with DAD detector
capillary electrophoresis with DAD detector
Firearm fumes (gunshot residua, GSR) - various metallic and non-metallic particles created by burning powder charge cartridges and igniters composition and the passage of the bullet in the head bore weapons. This includes and other debris swept shot during firing (rust preservative residues). Firearm fumes are visible at the moment of firing a flash or flame and smoke around the barrel firing weapons.
Part of GSR is recorded on the hands and clothing of the person firing on subjects close shots.
Exploring the GSR is especially important for determining distance shooting. The importance of having the assessment of suicide or self-harm. It is known that one can cause interference in the vitally important centers of the organism from a maximum distance of about 75 cm.
GSR which escaped through leaks in firing weapons, they together with firearm fumes leaked from mainly relevant when assessing whether a particular person is fired, or was near the shooting, eventually was shot in a certain area (room, means of transport, etc.). Likewise, the analysis firearm fumes important in assessing whether the firearm was at the time of shooting at a certain location or luggage.
As samples for expertise are then taken firearm fumes from various locations weapons around and shot himself out of the hands of the shooter. The main method of GSR analysis is the analysis using a scanning electron microscope. Particles that are a major part of GSR, have a characteristic shape and chemical composition.
Another methods of chemical composition analysis of GSR are chromatographic methods, capillary electrophoresis, methods of atomic spectrometry and mass spectrometry. Chromatographic methods and electrophoretic methods allow for the separation of chemical entities, creating a firearm fume as well as allow to perform the analysis of unexploded secured folds, charges amateurishly designed explosives, etc.
Fig. 1: The basic division Explosiv for forensic purposes
The scheme shows that explosives are arranged between the explosive and fuel, which in many cases is the major constituent of explosives prepared illegal homemade production. Furthermore explosive are divided into primary and secondary explosive. Primary explosive are very sensitive to initiation spark, flame, or mechanical force. Secondary explosive are generally less sensitive towards these mechanisms initiating explosions and their initiation typically occurs with primary explosive. Suitable tertiary explosive are then labeled substances and mixtures, which are relatively insensitive to initiation, e.g. NH4NO3. These substances require the presence of an additional component to detonate. Special groups of explosive homemade production, which are produced from precursors, are available from the explosives derived from criminal activity.
From the chemical point of view can be divided Explosive according to chemical structure and functional groups:
• nitrogen containing compounds (e.g. TNT) • aromates (Tetryl)
• esters of nitric acid (nitroglycerin) • peroxides (TATP)
• initiation explosive (lead styphnate) • salts (nitrate, urea),
• fuel / oxidizing component (ammonium nitrate / benzíd or ANFO). Examples of some structures of explosives are in Fig. 2.
Fig. 2: Examples of some explosive structures
Analysis of explosives and firearm fumes using liquid chromatography
Analysis of explosives and firearm fumes generally puts high demands on the collection, preparation, concentration and purification of the sample prior to analysis. Firearm fumes and unexploded detonators must always be subjected to extraction with two extraction agents (aqueous and organic). Water or aqueous buffers are used to extract water-soluble compounds such as inorganic ions or as sugars. Organic solvent acetone is used for most organic water insoluble component of explosives. Organic ballasts and disruptive component, which in this case is coextracted have to be than removed by further extract purification procedures. The specific purification procedure is chosen according to the end-analytical technique. Very often purification procedure using acetone as extraction solvent needs next purification by sorbent, which may include Porapak T or Florisil. Organic explosives are then captured on the selected sorbent, washed and eluted with a suitable organic solvent. Aqueous purification extracts are usually only filtration.
For some organic components Explosive is a suitable SPE extraction. The inorganic components may be captured on ion-exchangers Amberlite XAD-2, XAD-4, XAD-8 (ratio 1: 1: 1), C18 phases, phases and cyano- phenyl phases.
Task: Perform isolation, concentration and analysis of GSR and Explosive using HPLC-DAD and CE-DAD.
Chemicals: Explosiv standards in methanol at a concentration of 10 mg / L (TNT,
2,4-DNT, 2,6-2,4-DNT, RDX Tetryl), metal nitrates (copper, calcium, barium), methanol, acetonitrile, pyridinium sulfate, 1 M HCl, ammonium formate, deionised water.
Labware and tools: beakers, test tubes, Hamilton syringe, bottles for the mobile phase,
syringe filters with pores 45 microns, automatic pipettes and tips, vials and caps for LC and CE, ultrasound.
Parameters of LC separation
LC Column - Hypersil GOLD PFP, 1.9 um, 100 x 2.1 mm.
Mobile phase: A: 1 mM ammonium formate in water B: methanol Injection 2 mL, a detection wavelength of 214 and 254 nm.
Parameters of CE separation
Uncovered silica capillary 50 um inner diameter, total length 48.5 cm, effective length 40 cm,
Working electrolyte 10 mM pyridinium sulfate pH 7.0 Voltage of + 15 kV, injection of 100 mbar / 10s
Workflow:
Determination of calcium, barium and copper ions with CE-DAD
Firstly, presented sample fireworks first extract 10 mL of deionized water in a plastic container in ultrasound for 15 min. Filter the aqueous extract and use for analysis for the presence of inorganic metal ions using capillary electrophoresis with indirect UV-VIS detection.
2. Prepare a working electrolyte containing 10 mM pyridinium sulfate and adjusted to pH 7.0 with dilute hydrochloric acid.
3. Prepare a standard calibration solutions for barium, calcium and copper ions (use metal nitrates) in the range of 0.5 mg/L to 50 mg/L.
4. Set the capillary electrophoresis method CE_postblast.M and analyze standard calibration solutions and sample extracted according to the tutor.
Determination of organic constituents by LC-DAD
The second part of the first sample of the present extract in 10 ml acetone for 15 min sonication in a glass flask. Perform SPE extraction using C18 phases. User SPE extractor is attached. After extraction, the organic elute post blast residue using hexane.
2. After SPE extraction Collect the eluate into the prepared tube. The extract is evaporated under a nitrogen stream at 25 C to dryness. The residue after extraction Reconstitute in 200 ml of mobile phase, which will be used for the separation.
3. Prepare calibration solutions of organic substances (TNT, 2,4-DNT, 2,6-DNT, RDX Tetryl) in the concentration range of 0.5 mg/L to 50 mg/L
4. Use the tutor run the LC-DAD chromatograph method LC_postblast.M Measure and calibration solutions and sample to be extracted.
5. On the basis of the retention times of the standards and the separated substances in the extract perform the identification of individual organic substances in the sample.
For both methods to construct a calibration curve and make the determination of concentrations of metals and organic compounds in samples submitted.
Additional questions:
1. How can be analyzed the fireworks on the presence of unauthorized explosives (TNT, hexogen)?
2. What other types of detection in conjunction with liquid chromatography and capillary electrophoresis, it is possible to analyze metals and organic constituents of explosives?
Literature:
1. J. Bogusz, Forensic Science, 2000.
2. B.H. Stuart, Forensic Analytical Techniques, 2013.
