Cocaine and its substitutes studied with infra-red spectrophotometer
Author: Kevin P. O'BRIEN , , Robert SULLIVAN
Pages: 35 to 40
Creation Date: 1970/01/01
Robert SULLIVAN **
The further identification of cocaine and its many substitutes by the use of infra-red spectrophotometer is discussed in this article as a sequel to the paper concerning the identification of cocaine and other local anaesthetics with the use of X-ray diffraction which appeared in an earlier number of the Bulletin.1 It is important in forensic science to be able to differentiate conclusively between cocaine and the many non-narcotic cocaine substitutes, and this paper attempts to provide another valid method for distinguishing between these substances with certainty.
The data presented in the following infra-red spectrograms were initially analyzed with a Perkin-Elmer spectrograph model 237B. However, for presentation and printing purposes the older model, Perkin-Elmer 21, was used with very satisfactory results.
In attempting to identify unknown compounds with the use of infra-red spectrophotometer, the Sadtler reference file is sufficient for most cases, as was the ASTM file for X-ray diffraction. However, in cases where there is no existing spectra in the dadtler file, again, extra and repetitious identification procedures become necessary. The techniques used in the past to identify crystalline material have been found not to be sufficiently specific when one is working with small, irreplaceable amounts of chemical unknowns. It is with this realization of the need for additional reference spectra standards for certain known organic, crystalline substances not yet supplied in the Sadtler reference file (ASTM in X-ray diffraction) that this paper is written. Forensic chemists should then be able to establish a figure of merit, using X-ray diffraction and infra-red spectrophotometry for everyday performance and the spectra presented should make that figure of merit significant everywhere in law enforcement.
Assistant Professor of Police Science at Monroe Community College, Rochester, New York.
New York City Police Laboratory.
Bulletin on Narcotics, Vol. XX, No. 3.
Experimental: methods and materials
Quite acceptable I/R spectra have been obtained from small amounts of sample in this study. In adapting P/E infra-red spectrophotometer to this problem, 0.4 mg of dried, pure, known powder was mixed with 300 mg of chemically pure KBr on a wiggle bug (60 cycles/per sec) for three minutes. The mixed powder was transferred to the metal die and a partial vacuum suction applied for one-half hour. After the elapsed time, the die was subjected to 21,000 lbs/psi on a hydraulic molding press for one full minute. After the parameters were reduced to normal, the resulting KBr wafer was found to be completely transparent in most cases.
Excitation Perkin-Elmer I/R spectrophotometer, model 21 setting
Pen speed 560
Slit IX (Single)
Gain 5 ?
Chart speed 21/2-3
The above settings seem to be a convient compromise which provides fully usable data without the loss of important information.
Very satisfactory working spectra for the identification of cocaine and its substitutes have been developed using the infra-red spectrophotometer.
An experienced forensic chemist must always be aware that there is a slight discrepancy index due to internal characteristics of each particular instrument and the various parameters used in each instance. These small variations from the normal or expected readings are present when one wishes to re-examine or to duplicate the readings of another experimental datum.This discrepancy index should allow a slight correction to be made for the chance variations in the numerical intensities observed and here reported. These deviations do at times necessitate a wider selection of the number of stronger absorption peaks than one might wish in order to identify the unknown substance.
The extent or seriousness of this correlation is considered relatively small and completely independant among the many materials measured.
Once again the authors of this paper gratefully acknowledge and wish to thank Professor Lewis Wright, Chairman of the Department of Police Science at Monroe College and Captain Joseph P. McNally Commanding Officer of the New York City Police Laboratory for their continued interest and encouragement in our endeavours to apply scientific investigative tools as additional aids in modern criminal investigations.