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The illicit drugs were not detectable on the TLC plates using normal Raman spectroscopy. When the TLC spots of the drugs were analyzed with SERS, the spectrum was enhanced thus enabling direct drug iden@fica@on.
The Identification of Controlled Substances by TLC-SERS Kasey Cargill and Brooke W. Kammrath, Ph.D.
Henry C. Lee College of Criminal Justice and Forensic Sciences
Theory
Methods and Materials
Results Conclusions
References
Acknowledgements
Thin layer chromatography (TLC) combined with surface-‐enhanced Raman spectroscopy (SERS) proved to be an ideal method for separa@ng and iden@fying controlled substances and mixtures. This combined method adheres to the standards set forth by the Scien@fic Working Group for the Analysis of Seized Drugs (SWGDRUG) and is a rapid, reliable, and repeatable method of drug analysis. TLC is a separa@on method used as a screening test in forensic laboratories. This technique involves deposi@ng sample onto a planar sta@onary phase then using a liquid mobile phase that travels up the sta@onary phase by capillary ac@on. The ending result is a plate of spots that are the separated components of the mixture. Raman spectroscopy is an iden@fica@on method that examines the frequency change of a light source due to its interac@on with the sample. The major limita@ons to Raman spectroscopy are low sensi@vity and fluorescence interference. SERS enhances the scaOering procedure of Raman spectroscopy and corrects the disadvantages of normal Raman spectroscopy. The procedure mirrors that of normal Raman—the main difference being the addi@on of a silver nanopar@cle colloid. TLC-‐SERS is completed on a TLC plate by adding a metallic colloid to a separated TLC spot, and then directly analyzing the spot using Raman spectroscopy.
1) Szabo, N. J., & Winefordner, J. D. (1997). Evalua@on of two commercially available TLC materials as SERS substrates. Applied Spectroscopy, 51(7), 965-‐975. 2) Rana, V., Canamares, M. V., Kubic, T., Leona, M., & Lombardi, J. R. (2011). Surface-‐Enhanced Raman spectroscopy for trace iden@fica@on of controlled substances: morphine, codeine, and hydrocodone. Journal of Forensic Sciences, 56(1), 200-‐207. 3) Smith, E., & Dent, G. (2005). Modern Raman Spectroscopy-‐ A Prac=cal Approach. (pp. 113-‐127). West Sussex, England: John Wiley & Sons Ltd. 4) Pozzi, F., Shibayama, N., Leona, M., & Lombardi, J. R. (2012). TLC-‐SERS study of syrian rue (peganum harmala) and its main alkaloid cons@tuents. Journal of Raman Spectroscopy. 5) United States Department of Jus@ce, Drug Enforcement Administra@on. (2011). Scien@fic working group for the analysis of seized drugs (SWGDRUG) recommenda@ons. Retrieved from website: hOp://www.swgdrug.org/Documents/SWGDRUG Recommenda@ons 6.pdf
The authors would like to thank the University of New Haven Summer Undergraduate Research Fellowship for financially suppor@ng this research. We would also like to thank Dr. Chris Palenik (Microtrace) for sharing his knowledge on metallic colloids and Dr. John Lombardi (CCNY) for his meaningful discussions on the subject of TLC-‐SERS. Last, we greatly appreciate all of the faculty of UNH’s Forensic Science Department, and would like to especially thank Norma Hollender-‐Celico, the Forensic Science laboratory manager, for all of her help making this research a reality.
SUMMER UNDERGRADUATE
RESEARCH FELLOWSHIP
This research analyzed the illicit drugs cocaine, codeine, methamphetamine, and 3,4-‐methylenedioxy-‐N-‐methylamphetamine (MDMA). The drugs were mixed with caffeine for the drug mixture analysis. The same procedure was carried out on all of the above drugs. A sample of 0.100g was weighted out and placed in a glass vial. From the 0.100g of sample, 0.0100g was combined with 2.5mL of methanol to make a liquid solu@on. To confirm that the dispersive Raman spectrometer equipped with a 780 nm frequency-‐stabilized single mode diode laser was working properly, a polystyrene reference standard was analyzed daily. Substrate tests were also conducted using aluminum plates and silica gel on glass TLC plates. The solid samples and dried residues from the liquid solu@ons were tested using normal Raman spectroscopy and SERS using the following collec@on parameters: auto exposure with the signal to noise ra@o set to 500 and a maximum collec@on @me of 3 minutes. The normal Raman and SERS spectra were used as comparisons for the TLC-‐SERS spectra of the drugs and mixtures. To analyze using TLC-‐SERS, the liquid solu@on was spoOed on a TLC plate, then separated using a 9:1 chloroform to methanol TLC bath. The spots were found using a short wave UV light. The sample spots were analyzed using normal Raman spectroscopy. To perform the SERS analysis, a drop of silver colloid was placed directly onto the TLC plate spot then analyzed with the Raman spectrometer. This procedure was conducted for all four drugs and for the separated drug mixtures.
Future Work Addi@onal research experiments will be conducted using different illicit drugs and drug mixtures. An inves@ga@on into the use of gold colloids, rather than silver colloids, for SERS enhancement will be explored. Also, the authors will evaluate the limits of detec@on for this technique. Last, research focusing on the detec@on of illicit drugs in body fluids using both normal Raman and SERS spectroscopy will be explored.
TLC-‐SERS proved to be a successful method for the separa@on and iden@fica@on of controlled substances and controlled substance mixtures. This combined technique has the poten@al to greatly benefit the forensic science community because it requires less sample, @me, and money when compared to other methods of illicit drug analysis and conforms to the currently accepted standards of drug iden@fica@on set forth by SWGDRUG.
Cocaine: normal Raman vs. SERS
Figure 2 shows two spectra for the analysis of cocaine. The top is the normal Raman spectrum of cocaine while the boOom is the SERS spectrum of cocaine.
MDMA: TLC-‐normal Raman vs. TLC-‐SERS vs. SERS
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Figure 4 shows three spectra for the analysis of MDMA. The top is a normal Raman spectrum of a MDMA spot on a separated TLC plate. The middle is a SERS spectrum of a MDMA spot on a separated TLC plate. The boOom is a SERS spectrum of MDMA on an aluminum slide.
Cocaine: TLC-‐normal Raman vs. TLC-‐SERS vs. SERS
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Figure 3 shows three spectra for the analysis of cocaine. The top is a normal Raman spectrum of a cocaine spot on a separated TLC plate. The middle is a SERS spectrum of a cocaine spot on a separated TLC plate. The boOom is a SERS spectrum of cocaine on an aluminum slide.
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Silver Colloid Prepara@on
Figure 1 shows the silver colloid being prepared. The pictures were taken in 10 minute increments. The colloid is composed of two solu@ons: the first being 0.170g silver nitrate and 1.00L deionized water and the second being 1.00g sodium citrate and 0.100L deionized water. 50.0mL of the silver nitrate solu@on was heated to a boil, and then 1.00mL of sodium citrate solu@on was added. The solu@on was heated for one hour.