Chemistry ERT on Forensic Science

This article discusses the use of mass spectrometry, thin layer chromatography, and infrared spectroscopy in forensic science investigations. It includes experimental procedures and results, as well as a summary of the findings.

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Introduction
Investigations are needed to be done by a forensic chemist over allegations of a crime. The local
police have presented to the forensic chemist a brief that encompasses the evidence that has been
gathered at the scene and any other information from witnesses that may be deemed relevant.
The investigations are to be done in line with an explosion and a crash that has been experienced
with a Compass flight 245. The evidence that has been collected from the site of the crime
includes a sample of a suspicious residue that has been found near the site of an explosion in
Row 9 as well as a passenger manifesto.
The suspicious residue is the evidence that has been sent to the lab for investigation and analysis
to provide a hint on the probable cause of the explosion. Following the nature of the explosion
and the suspicious residue, the detectives sent to the crime scene believed that the explosion was
as a result of the victim in Row 9 carrying a heart medication. The detectives have instead ruled
out the possibility of the victim carrying a bomb and hence distanced the explosion from bomb
attacks.
Test 1: Mass Spectrometry
Mass spectrometry is applicable in the determination of the molecular weight of molecules as
well as the elements that are found in the structure of the molecule. To conduct a mass
spectrometry test on a compound or mixture, the substance must be flash vaporized first through
gas chromatography in order to separate the impurities. The evaporated compound is then
bombarded using particles that have very high energy which drive the molecules which were
initially neutral to ain a charge (Orphanou 2015).

Through an electric field, the ions are accelerated and sorted by their masses and charges with
the aid of the relationship between mass force and velocity in the classification of the ions. Since
the acceleration attained by an object is normally inversely proportional to the mass of the object,
it means a heavier ion will travel at a relatively lower speed than a lighter ion. The generated
spectrum illustrates the relative abundance of ions against the charge or mass ratio which is the
same as the grams per mole (Manheim et al., 2016). The molecular weight of the molecule is
represented by the peak of the molecular ion.
Just like infrared spectroscopy, mass spectrometry is applicable in this investigation as it would
aid in the determination of the molecular weight of the components of the unknown compound.
These molecular weight values would then be compared against known molecular weights of
substances and compounds and hence a determination of the identity of the suspicious residue.
The experimental part of this test would entail putting a drop of the suspicious residue in a 50
mL Erlenmeyer flask and then 5.0 mL of acetone is added to the flask and the contents swirled.
About 1.5 mL of the mixture is removed upon ensuring that the contents of the flask have been
properly swirled to obtain an even mixture. The removed portion is used for washing out the
mass spectrometry vial (Calvo-Castro, Guirguis & Stair 2018). This is done to ascertain that
there are no impurities in the sample solution. The vile was then filled to the third line with the
solution upon being thoroughly rinsed, capped and suitably labeled. A spectrum illustrating the
molecular weight was produced upon running the sample through the mass spectrometry.
Results

Figure 4: Mass Spectrometry of the Unknown Compound
The spectrum generated from the mass spectrometry, as illustrated in the figure above,
demonstrates the molecular weight of the suspicious sample. The molecular ion peak which is
observed on the farthest right shows a molecular weight of 98 g/mol (Lauzon et al., 2015).
Conclusion
The mass spectrometry is carried out to establish the molecular formula and weight of the
unknown compound. Upon the completion of the thin layer chromatography process which aided
in flash vaporizing the molecule to ascertain that all the impurities are eliminated, the evaporated
unknown compound is then hit using particles that have high energy and then subjected to an
acceleration phase which served to classify the ions based on the ration of the masses to charges.
Test 2: Thin Layer Chromatography

Thin Layer Chromatography is one of the techniques of chromatography that is applied to the
separation of various non-volatile mixtures. This test would be applied in this investigation in
separating the different non-volatile substances that might be found in the suspicious residue.
The test is ideal for the investigation owing to its ability to separate mixtures that are not volatile.
This means that the residue that was obtained from the crime scene could easily be tested and the
various substances that make up the mixture established through Thin Layer Chromatography
(Tang et al., 2015).
Thin Layer Chromatography is carried out on a sheet of glass, an aluminum foil or even a plastic
that is often coated using a thin layer of an adsorbent material that is mostly aluminum oxide,
cellulose or silica gel (Illiano et al., 2018). The adsorbent layer is called the stationary phase.
Through capillary action, a solvent or mixture of the solvent that is often referred to as the
mobile phase is drawn up the plate upon the application of the sample on the plate. Owing to the
different rates of the ascension of the various analyte of the Thin Layer Chromatography plate, a
separation would thus be attained. The mobile phase is composed of properties that are distinct
from the stationary phase. An example is where heptane is used as a non-polar mobile when
silica gel which is a very polar substance is used. The mobile phase could be composed of a
mixture to enable the chemist to fine-tune the bulk properties of the mobile phase (Lawton et al.,
2017).
At the stationary point, a matrix that is specially and finely ground is coated using a glass plate
which is as thin as about 0.25 mm. besides, a binder such as gypsums is mixed into the stationary
phase to enable it to stick properly to the slide. In most cases, a fluorescent powered is often
mixed into the stationary phase to make the process of visualization simpler at later stages of the
test.

Principle
Just like the other chromatographic methods, Thin Layer Chromatography is based on the
principle of separation in which the separation is a factor of the relative affinity of the
compounds towards the stationary and the mobile phase (Mistek & Lednev 2015). The
compounds or mixtures that are under the influence of the mobile phase move over the surface of
the stationary phase during which the mixtures that have a higher affinity for the stationary phase
travel at a relatively slower speed even as the others travel at higher or faster speeds. This then
achieves the separation of the components that are found in the mixture. Upon the completion of
the separation process, the individual components of the mixture can be visualized as spots at
various levels of travel on the plate. The nature or the characteristics of the spots are identified
with the aid of an appropriate technique for detection (Hood et al., 2018).
Results from the test
Figure 1: Chromatography Chart

Figure 2: Rf values for plates that had more than one resolves spot
Analysis
The various components of the mixture of the suspicious residue, observed as separated spots
were identified by comparing the distances they traveled against those of known reference
materials. The distance of the start line was measured to the solvent front (=d). The distance of
the center of the spot was then measured to the start line (=a). The distance of the solvent moved
was then divided by the distance moved by each of the individual spot and the resultant called
the Rf value, the resulting ratio.
Conclusion
The results obtained from this experiment demonstrated that polarity of the substance used is a
fundamental deciding factor as to the traveling of a component of a sample on a TLC plate.
When the mobile phase is non-polar, the non-polar components if the sample would travel very

far up to the TLC plate as compared to the polar components. Should the mobile phase be very
polar, the polar components will then travel a greater distance up the TLC plate as compared to
the non-polar components? Generally, the components that were making up the mixture of the
suspicious residue were found to be more polar than non-polar with each of them having a
different polarity from the other (Ewing & Kazarian 2017). The Rf values of each of the spots
were as shown in the results table and since none of all the seven plates had four spots resolved,
it was not possible to assign the TLC spots to any of the reference materials. The findings for this
test were thus in contravention of the hypothesis that was made by the detectives.
Test 3: Infrared Spectroscopy test
Infrared Spectroscopy is a chemistry analysis technique that is based on the principle of
absorption of infrared energy by the molecular species and the accompanying excitation of the
modes of vibration of the molecule. (Sombut et al., 2018) The absorption transition mechanism
finds a basis on the interaction of bond dipole found in a molecule with the electric field of the
incident photon. It revolves around the analysis of the interaction of the infrared light with a
molecule, a process that can be conducted in three distinct ways: emission, reflection, and
absorption. Infrared Spectroscopy takes measurements of the vibrations of the atoms and uses
such findings in the determination of the functional groups. The technique is applicable in this
investigation as it would be able in differentiating the various types of functional groups that are
found in the suspicious residue. Components that have stronger bonds and light atoms would
generally have a higher stretching frequency as compared to those with weaker bonds and heavy
atoms.

The determination of the functional group that is present in the suspicious residue us important
as such information are usable in the determination of the molecular weight of the compound
besides its architecture. Covalent bonds have various rates of absorbing infrared radiation, which
is a factor of the masses of the included atoms as well as the strength and the polarity of the
bonds that have been included (Ellen, Day & Davies 2018). Hence by running infrared radiation
on the unknown or suspicious residue and taking measurements of the absorbance at various
wavelengths, light is shed on the different bonds that exist between the atoms that are found
within the compound. The spectrum that is generated is relative absorbance against the
wavelength. This technique, when combined with mass spectrometry would aid in the
determination of the molecular formula as well as the structure of the suspicious residue.
The experimental procedure as would be conducted in the laboratory would entail labeling the
suspicious residue as#M20. The suspicious residue is first run through Infrared Spectroscopy.
The ATR sampler is then cleaned with acetone and a kine's wipe before a single drop of the
suspicious residues is placed on the ATR sampler. The program is then run and thereafter an
Infrared Spectrum is generated (Kanu et al., 2015).
Results of the test
Infrared Spectroscopy of the Suspicious Residue

The spectrum shown in the figure above depicts that the suspicious residue has a ketone function
group as of the compound. This can be shown by the very intense peak which tends to be about
1704 wavenumbers representing the carbonyl bond. The results of the infrared spectrometry
determined a ketone functional group as opposed to an ester due to the peak that appeared to be
less than 1730 wavenumbers.
Conclusion
The infrared spectroscopy is used in the determination of the functional group of the suspicious
residue. Since all the bonds have various mechanisms of absorbing the infrared light, the
measurements achieved during radiation are used in the determination of the nature of the
bonding that is found within the unknown compound.
Summary
Through a collective analysis of all the spectra generated from the three techniques that have
been used in this investigation, the suspicious residue can be identified. The first puzzle involved
the identification of the functional group which was determined to be a ketone because of the

carbonyl peak which was at about 1704 wavenumbers. A combination of this information with
that which is presented in the mass spectra aids in the discovery of the molecular formula of the
suspicious residue. Upon observing the mass spectra as shown in the figure, the peak of the
molecular ion appeared at 98 g/mol. The molecular formula of the unknown compound was
determined by subtracting the molecular weight of the functional group from the total molecular
weight.
The findings from the three tests are not supportive of the hypothesis made by the detectives.
The tests show a heavy atom with strong bonds which can be attributed to a mono-substituted
six-carbon ring that has double bonded oxygen that is representative of the ketone functional
group.

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