Thanks for the explanation and link Pseudo G.
...and to rah for the effort.
Pseudo G is right on the water thing. When preparing a KBr Infrared, where potassium bromide is mixed with the sample, the KBr must be anhydrous. It's common to dry it in a desiccator for a day or 2 before using. Many types of IR spectrometers exclude moisture during the analysis by purging the sample chamber with Nitrogen to reduce any CO2 or H2O.
Before turning to rah's attachment, I should point out that identifying several components in a single sample can be bloody difficult, particularly without
some idea of what you expect to find. A statement in the paper by Coates serves to illustrate an important point;
One important factor to bear in mind is that a successful interpretation is based not only
on the presence of particular bands within the spectrum,
but also the absence of other important bands. Complete
classes of compounds can be rapidly excluded during the
interpretation by the use of no-band information….
… One of the main challenges in presenting a text on spectral
interpretation is to form a balance between the theory
that is needed to appreciate the links between molecular
structure and the observed spectrum and the practice...
Interpretation using comparison spectrograms of pure samples or recognition software, allows a more precise match up of multiple absorption peaks. But it would be a tall order, even for a limited range of expected substances mixed together, to be able to manually pick out and determine what peak represents what functional group belonging to what substance.
I'm sure there are those with years of experience -and are very good - with multiple compounds. However, to avoid the guessing factor, other techniques would normally be employed which would make the IR results more meaningful. A lab without recognition software or a samples database could use techniques such as high performance liquid chromatography (HPLC) to separate the compounds before an IR spec was done. Successful chromatography would give relatively pure samples of compounds from which an IR of each eluted compound would then reveal good detail.
If you read the excellent paper on IR on pseudo G’s above link, you’ll see on pages 2- 3 that different types of chemical bonds can create different types of interference to the IR signal. This means that the total Energy term is comprised of these various molecular influences on the transmitted IR energy. So, while absorption characteristics are mostly responsible observed characteristics, absorption is only
part of the overall energy change – the IR signature- from which a molecule
can be identified.
E total = E electronic + E vibrational + E rotational + E translational
2 THE ORIGINS OF THE INFRARED
SPECTRUM
In the most basic terms, the infrared spectrum is formed
as a consequence of the absorption of electromagnetic
radiation at frequencies that correlate to the vibration of
specific sets of chemical bonds from within a molecule.
First, it is important to reflect on the distribution of energy
possessed by a molecule at any given moment, defined as
the sum of the contributing energy terms (Equation 1):
E total = E electronic + E vibrational + E rotational + E translational
.1/
The translational energy relates to the displacement of
molecules in space as a function of the normal thermal
motions of matter. Rotational energy, which gives rise
to its own form of spectroscopy, is observed as the
tumbling motion of a molecule, which is the result of
the absorption of energy within the microwave region.
The vibrational energy component is a higher energy
term and corresponds to the absorption of energy by a
molecule as the component atoms vibrate about the mean
center of their chemical bonds. The electronic component
is linked to the energy transitions of electrons as they
are distributed throughout the molecule, either localized
within specific bonds, or delocalized over structures, such
as an aromatic ring. In order to observe such electronic
transitions, it is necessary to apply energy in the form of
visible and ultraviolet radiation (Equation 2):
2/ E = hv frequency /energy .
With the IR spectra of a mixture of compounds, such as that posted by rah, absorptions for various functional groups making up the different substances will often overlap. This means that a particular functional group of substance X will be masked by one on substance Y. Combined peaks from X & Y may also present many peaks with few spaces, thereby 'crowding' the result. From the earlier mentioned quote from Coates;
a successful interpretation is based not only
on the presence of particular bands within the spectrum, but also the absence of other important bands.
Lets turn now to spectra from a few of the substances mentioned. rah also said via PM that the analyst thought psilocybin may be present.
As the water component in the rah’s result is so high, upper band resolution (3570 –3200 cm-1) is really affected by O-H stretching. So, lets look at the region below 2000 cm-1.
There is considerable detail in the region, but it’s often the most difficult to correctly resolve. rah's sample contains many peaks around this region which overcomplicates the spectrogram. So rather than try to allocate and explain various functional groups (as seen in the tables in Coates’s paper), lets instead compare spectrograms of known and suspected samples, to rah’s IR spectrogram
Comparison of “Blue Daffy Duck” IR spectra to MDMA IR spectra
Comparison of “Blue Daffy Duck” IR spectra to Methamphetamine IR spectra
Comparison of “Blue Daffy Duck” IR spectra to Psilocybin & DXM IR spectra
For all 4 comparisons, the circled areas on the "blue daffy duck" spectrogram were those numerically closest to the stated principle wavenumber peaks.
I can’t locate a reference for any of the DMA isomers, but as previously mentioned, I doubt very much this would be present and looking at the relevant expected positions of the functional groups, I don’t see expected methoxy ether peaks around 2820-2810 cm-1
These pictures don’t really explain what is in the tablet, but they should serve to illustrate what can be expected from different IR’s of the same compound. While there is some variation often noticed between results from different machines, this should normally not be a problem, as a pure sample is often used as a reference.
It certainly appears there is more than one compound present in the blue daffy ducks, as well as too much water in the prepared sample. The sample really needs to be run again, preferably by first separating the major components.
IR info from "Clarke's Analysis of Drugs and Poisons"
I should also add; in matching wavenumbers of the "daffy duck" spectrogram, only one peak directly corresponded to a peak listed in Clarkes (DXM), however, this in no way confirms DXM was present.
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