Detection and analysis of aromatic nitro compounds like TNT, DNT, and picric acid are important for forensic science. The document discusses several methods for detecting these compounds including dogs, colorimetric tests, and technologies like mass spectrometry, X-rays, and CT scans. Instrumental techniques for analysis are also covered, including NMR, neutron activation analysis, gas chromatography-mass spectrometry, and UV-visible-NIR spectroscopy. Detection dogs remain very effective for detecting explosives due to their sensitivity, while colorimetric tests provide rapid on-site detection through characteristic color changes. Advanced technologies like CT scans and mass spectrometry also allow for sensitive detection and analysis in both field and laboratory settings.

1. Forensic Analysis and Detection of
Aromatic Nitro compounds (TNT, DNT
and Picric Acid)
By: CHHAVI KAUSHAL
M.SC FORENSIC SCIENCE AND CRIMINOLOGY
3RD SEMESTER

2. Contents
• Introduction
• Detection
• Analysis
• References

3. Aromatic Nitro compounds
• Aromatic nitro compounds are generally stable but are frequently reactive,
especially if they contain groups other than nitro groups in the meta position
with respect to one another. As a class they constitute the most important of
the military high explosives. They are also used as components of smokeless
powder, in compound detonators, and in primer compositions.
• The nitro compounds are poisonous.

4. TNT- (2,4,6-trinitrotoluene)
• TNT is also produced by the C-
nitration process. It is formed by the
nitration of toluene with mixed nitric
and sulphuric acids. Toluene is first
nitrated to mono-nitrotoluene and
then to di-nitrotoluene and finally it
gets converted to crude tri-
nitrotoluene.

5. Picric Acid (2,4,6-trinitrophenol (TNP))
• Picric acid is basically prepared by
dissolving phenol in sulphuric acid
and then nitrating the product with
nitric acid. In this reaction
Sulphuric acid act as an inhibitor of
the nitration.

6. 2,4-Dinitrotoluene (DNT)
• DNT is an organic compound
which is pale yellow crystalline solid
is well known as a precursor to
TNT but is mainly produced as a
precursor to toluene diisocyanate.

7. Detection
Detection can be on site or in the laboratory. There are several ways of detection:
• Detection of Explosives by Dogs
• Colorimetric Detection of Explosives
• Nuclear Technologies
• X-ray Technologies
• CT Technologies
• Analysis and Detection of Explosives by Mass Spectrometry
• Detection of Explosives Using Amplified Fluorescent Polymers

8. Detection of Explosives by Dogs
• Detection dogs are very widely used and have many practical advantages. They have been
successfully used for many functions, including detection of drugs, illegal food imports,
explosives, arson and human remains.
• One of the most effective and available technologies employed for the detection of explosive
materials is the explosive detection dog (EDD) and handler team.
• Dogs have a long history of use by law enforcement agencies for a variety of detection tasks, and
are considered to be one of the most sensitive detection instruments available; EDD teams are
currently considered accurate, durable, flexible and are one of the most accessible technologies
for conducting explosive detection tasks.
• Many federal agencies, such as the Transportation Security Administration, the United States
Secret Service and Department of Defense, as well as state and local agencies currently use EDD
teams in their efforts to interdict explosives.

9. Example dog’s
response to
vapor
constituents.

10. Colorimetric Detection of Explosives
• Color reactions have been extensively used in the field of explosives analysis. Their application is
easy and the equipment required is simple and inexpensive.
• Their sensitivities are often in the sub-microgram range. They enable rapid, on-site diagnostic
detection of explosive materials, and are also used for preliminary laboratory tests of materials
suspected of being explosive. Moreover, these tests can help in diagnosing impurities and
degradation products of explosives.
• It has been known for a long time that polynitroaromatic compounds produce colored products
in contact with alkalis.
• In the Janowski reaction, a solution of the polynitroaromatic compound in acetone is treated
with concentrated aqueous KOH solution. 2,4,6-trinitrotoluene (TNT), treated with 30%
aqueous KOH, produced red color, sodium sulfite for 2,4-DNT (blue-purple color) and picric
acid shows yellow colour.

11. Nuclear Technologies
• Nuclear explosive detection approaches typically use particles to probe the nucleus
of the target material. The interrogation procedure involves the measurement of
transmitted/emitted neutron or gamma radiation.
• The selection of an appropriate radiation detector can be a very important part of a
detection technique.
• Trade-offs in the detector selection involve the sensitivity of the detector,
interferent reactions, cost of the detector material, logistic issues such as the need
for cryogenic cooling, and possibility of radiation damage to the detector during the
measurement process from other types of radiation in the operational environment

12. X-ray Technologies
• X-ray systems provide a unique ability to detail images of the contents inside
parcels. An experienced operator of such systems gleans a wealth of
information from X-ray images and recognizes a wide variety of objects,
both dangerous and innocuous, from the projected image.

14. CT Technologies
• X-ray computed tomography
(CT), initially developed for
medical diagnostics, is now also
being used extensively in airports,
worldwide, to find hidden
explosives in checked airline
luggage.

15. Forensic Analysis
Instrumental Techniques Employed in Forensic Chemistry
1) Nuclear Magnetic Resonance Spectrophotometry
2) Neutron Activation Analysis
3) Gas Chromatography Mass Spectroscopy
4) UV- VIS- NIR Spectrophotometry, etc.

16. Nuclear Magnetic Resonance
Spectrophotometry
• The basic principle of NMR is that
nuclei of certain molecules absorb
radiation of the region of radio
frequency in strong magnetic fields.
In this way the identification of
traces and even impure samples is
made on the basic principle that
nuclei of some molecules absorb
radiation of a definite frequency.

18. Neutron Activation Analysis
• In NAA, a beam of neutrons from a
nuclear reactor is directed at a sample of
test material. The material becomes
temporarily radioactive, emitting γ -rays
that are characteristic of the composition;
analysis of the γ -radiation provides a
highly accurate and reproducible
determination of the content of the
sample. The determination of arsenic in
the hair of dead bodies buried that are
burried for hundreds of years are made
possible by this technique.

20. Gas Chromatography- Mass Spectroscopy
• Another useful technique that is
employed in simultaneous separation
and qualitative as well as quantitative
analysis of one or more components
of an unknown sample is GC-MS. A
GC-MS is actually two instruments
that are physically clubbed together, in
a single unit, the so-called "tandem" or
"hyphenated" techniques.

22. UV-Vis-NIR spectroscopy
• UV-Vis-NIR spectroscopy is used to test for certain abused drugs. UV-visible-NIR
microspectrophotometers are instruments able to measure the spectra of microscopic samples. It can
be used to compare questioned samples of the evidences with the known ones. They are also
employed in analyzing the papers and inks of questioned documents and to determine the
characteristics of microscopic glass fragments. As these samples are not altered, UV-Visible-NIR
micro-spectroscopy is considered a non-destructive technique.

24. References
• www.nature.com
• www.wikipedia.com
• Maurice Marshall Jimmie C. Oxley - Aspects of Explosives Detection-
Elsevie – book
• www.pgpathshala.in