Skip to main content
Chemistry LibreTexts

Student's Notes

  • Page ID
    66451
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Detection of Trace Organic Explosives by Solid Phase Extraction and Liquid Chromatography

    References

    Thompson, R.Q.; Fetterolf, D.D.; Miller, M.L.; Mothershead, R.F. “Aqueous recovery from cotton swabs of organic explosives followed by solid phase extraction,” J. Forensic Sci. 1999, 44, 795-804.

    Yinon, J.; Zitrin, S. Modern Methods and Applications in Analysis of Explosives; Wiley: New York, 1993.

    Saferstein, R. Criminalistics: An Introduction to Forensic Science, 6th edition, Prentice-Hall 1998; pp 326-360. {explosives}

    Simpson, N. “Solid phase extraction: disposable chromatography,” Am. Lab. 1992, August, 37-43. {solid phase extraction}

    Skoog, D.A.; Holler, F.J.; Nieman, T.A. Principles of Instrumental Analysis, 5th ed.; Saunders: Philadelphia, 1998; pp 725-735, 739-744. {liquid chromatography}

    Goal

    To identify and semi-quantitate any organic high explosives remaining at a post-blast crime scene.

    Suggested Method of Analysis

    Collection of the explosives from a surface by wiping with a wetted cotton swab; isolation of the explosives by solid phase extraction; analysis of the extract by reverse phase liquid chromatography using a diode array detector

    Available Standards

    HMX 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclohexane
    RDX 1,3,5-trinitro-1,3,5-triazacyclohexane

    Tetryl

    2,4,6-trinitrophenylmethylnitramine
    EGDN ethyleneglycoldinitrate
    NG glyceroltrinitrate

    PETN

    pentaerythritoltetranitrate

    TNT

    2,4,6-trinitrotoluene

    DNT

    2,4-dinitrotoluene

    NT

    4-nitrotoluene

    Collection of the Explosives

    Wet a clean cotton ball with 0.50 mL of 50:50 water:methanol. Swab the surface of the post-blast debris with a cotton ball to collect the explosives residue. Rotate the swab occasionally as you wipe in order to use all of its surface. Next, extract the captured explosives from the cotton ball into water. Place the cotton ball at the bottom of a 10-mL plastic syringe, draw 10 mL of water into the syringe, let the syringe stand for 15 minutes, and finally push the water from the syringe into a collection tube.

    Solid Phase Extraction

    Apply solid phase extraction to the 10-mL extract to isolate the organic explosives. A 3-mL, Waters Oasis sorbent, SPE tube is conditioned, loaded with extract, washed, and explosives eluted with methanol. Follow the procedure outlined in the table below. Flow rates are maintained by adjusting the vacuum applied to the SPE manifold.

    STEP

    REAGENT

    VOLUME

    FLOW RATE

    Condition

    methanol

    water

    10 mL

    10 mL

    5 mL/min

    5 mL/min

    Load Sample cotton ball extract 10 mL 2 mL/min
    Wash 75:25 water:methanol 3 mL 2 mL/min
    Elute methanol 1 mL <2 mL/min

    Volume Reduction and Solvent Exchange

    Add 0.1 mL of water to the 1-mL methanol eluate. The volume is reduced to less than 0.25 mL by heating the liquid to 60 oC while passing nitrogen over it. Next, 0.50 mL of water are added to the solution to lessen the strength of the sample solvent for subsequent injection into the liquid chromatograph.

    Liquid Chromatography

    Prepare a standard solution containing each of the eight explosive compounds at 2.0 μg/mL in 50:50 water:methanol solvent. Separate standards and samples for 20 minutes under the following conditions:

    Injection Volume

    Mobile Phase

    Flow Rate

    Column

    Detector

    50 μL 50:45:5 mixture of water: methanol:acetonitrile 0.8 mL/min C18, 15 cm, 4.6 mm i.d., 5 μm particles 200 – 250 nm ; monitored @210 nm

    Data Analysis

    Qualitative analysis: perform a spectrum analysis of the standards and unknowns to confirm the identity of the unknown explosives. Visually compare the pairs of spectra.

    From the results of the qualitative analysis and the table below determine the type of explosive material that may have been the cause of the explosion under investigation.

    Material

    Composition

    Cyclotol

    RDX, TNT

    Semtex

    RDX, HMX, PETN

    Tetrytol

    Tetryl, TNT

    Triple-base propellant NG, DNT

    Semi-quantitative analysis: by comparing the peak areas of the components of the standard with the peak areas for each of the identified unknown compounds in the sample and by accounting for the volume changes, calculate the mass of each explosive found on the post-blast debris.


    This page titled Student's Notes is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Contributor.

    • Was this article helpful?