Pressed Bromide Method of Infrared Spectrographic Analysis of Narcotics
IDENTIFICATION OF A NARCOTIC
PRESENTATION OF NARCOTIC SPECTRA
Author: James J. Manning,
Pages: 85 to 86
Creation Date: 1955/01/01
Atlas of Infrared SpectraPh.D. James J. Manning, Chief Physicist and Chemist, Police Laboratory, City of New York
A search of the literature will reveal the absence of the infrared absorption spectra of many of the important alkaloids. We present herein the infrared spectra of a group of the most important narcotics. We wish to call attention to the infrared spectra as a specific, critical and direct method of identification of narcotics. The degree of specificity and the great variations which exists among the infrared spectra of these narcotics indicate graphically how useful this method should be also in the determination of the origin of the natural, synthetic and illicit narcotics.
The spectra presented were obtained on a Perkin-Elmer model 21, recording, double beam, optical null, infrared spectrometer. The wavelength range is from 2 to 15 microns. The spectra are directly comparable since they have all been obtained from equal amounts of narcotics, unless otherwise indicated. The samples contain 0.002 gm. of narcotic mixed with 0.998 gm. of spectral pure potassium bromide. From the 1.000 gm. mixtures, thoroughly pulverized, 0.600 gm. were weighed and were pressed into 13 mm. discs in a special KBr die under 20,000 P.S.I. pressure. These discs were mounted directly in the light path of the infrared spectrometer by means of a micro-sample adapter. Descriptions of the sampling equipment and techniques can be obtained in the references (1) and (2) cited in the bibliography.
The term "fingerprinting" has been applied to many identification processes of animate and inanimate objects, but the infrared spectrum reveals more than the identity of a material. It is a unique and characteristic property of that substance based upon the fundamental functional groupings in the molecule. In addition the spectrum of a mixture of mutually non-reactive pure substances is the summation of the absorption bands in the spectra of the components.
In the infrared spectrum the characteristic bond vibrational bands are readily recognized even in chemical molecules as complex as those of rubber or the proteins. The spectra of the infrared region 2 to 15 microns are due essentially to the vibrational motion of the atoms within a molecule, and the absorption frequencies characteristic of definite bonds may be conveniently termed "bond vibrational frequencies". The binding forces of the atoms in the molecule are influenced in definite ways by the structural environment of the bond and their study is capable of lending itself to the solution of the chemical problems of structure elucidation, identification and quantitative analysis.
In order to identify an unknown narcotic, its spectrum is first compared with the spectra of known standard substances, such as the spectra presented in this paper. If the unknown narcotic is a substance for which the spectrum has been recorded, the identification pressents little difficulty, especially if it is recorded in accurate amounts and listed among the substances in the American Society of Testing Materials, I.BM. card system. Should this be unsuccessful then an attempt is made to analyse the spectrum on the assumption that the unknown narcotic is a mixture. The components of the mixture are then considered, which mixed together, would yield the same absorption bands in the spectrum of the unknown narcotic mixture. The conclusions may readily be substantiated by obtaining the spectra of such mixtures for comparison.
To expedite the work of comparison between known spectra and unknown spectrum, preliminary classification of the unknown as to type can be made by consideration of the prominent features of the spectrum which often reveal the nature of the unknown narcotic.
A detailed consideration of the individual group frequencies may be obtained by reference to the publications listed in the bibliography. These few paragraphs are a general résumé of the structural information to be derived from the various regions of the spectra.
The absorption from 15 microns to 7 microns is associated principally with the stretching vibrations of C-O and C- O bonds and deformation vibrations of C-H bonds. These are sensitive to small changes in molecular structure and this region is of great use for identification by empirical comparison of the spectra. This region has been called the "fingerprint' region due to the high specificity of the more prominent bands, believed to be associated with localized molecular vibrations. Many important types of group vibrations have been established but the detailed treatment of this region remains to be elucidated.
In the region from 8 to 7 microns occur band characteristics of methyl and methylene groups. This region of the spectrum is particularly useful for the recognition of free methylene groups adjacent to carbonyl groups.
The region below 7 microns contains strong absorption bands associated with C=O stretching vibrations and weaker C=C stretching bands. This region of the spectra has been studied in considerable detail and has proved fruitful in identifying carbonyl functions and unsaturated centres from the positions of the band maxima.
Below 6.5 microns there occurs absorption associated with the stretching vibrations of C-H and O-H bonds.
The aliphatic C-H bonds of methyl and methylene groups give rise to strongly overlapping bands between 4 and 3 microns. The complex contour of this band envelope shows great variation with the molecular structure and is useful in providing supplementary evidence for identification purposes.
The spectra are recorded from 2 to 15 microns on a linear scale of wave number units with the absorbance (optical density) increasing downwards on a logarimetric scale.
Figures 1 to 6 show the infrared spectra of the narcotic alkaloid, printed on each spectra.
Figures 7 to 12 show the infrared spectra of six synthetic narcotics.
Figures 13 to 18 show the infrared spectra of both the sulfate and hydrochloride salts of morphine, cocaine and codeine.
Figures 19 to 21 show the infrared spectra of narcotics mixed with a dilutant (lactose) in the quantities indicated.
Figures 22 and 23 show the infrared spectra of cocaine mixed with a dilutant (lactose) and an adulterant (quinine sulfate) in the quantities indicated.
Figures 24 to 26 show the infrared spectra of the substances used in the mixtures.
A specific, critical and direct method of identifying narcotics has been illustrated by the presentation of infrared spectra based upon quantitative measurements and recorded on a double beam, optical null, infrared spectrometer.
The features of this method of analysis are ideally suited to the determination of the origin of natural, synthetic and illicit narcotics.
The preliminary phase in the determination of narcotics in the presence of dilutants and adulterants has been presented by a series of infrared spectra.
The author wishes to acknowledge the co-operation and assistance of Messrs. M. Grafton, H. Sternglanz, F. DuPaul, J. O'Connell, K. O'Brien and J. Russo.
Appreciation and thanks is expressed by the author to the pharmaceutical and chemical companies for their gifts of samples.
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