Dual Wavelength 785nm and 1064nm excitation Portable Raman Spectrometer: RAPID AUTHENTICATION OF GENUINE AND COUNTERFEIT PHARMACEUTICALS
Posted on October 15, 2014
Overcoming fluorescence interference in counterfeit Pharmaceutical samples is achieved using a dispersive, dual wavelength xantus®-2 portable raman spectrometer, equipped with both 785nm and 1064nm laser excitation. the dual wavelength system affords the opportunity for selection of an appropriate excitation for rapid identification of a wide range of genuine and counterfeit pharmaceuticals.
Counterfeit pharmaceuticals are a global problem and include products containing potentially harmful substances but also products that contain no or diluted amounts of active pharmaceutical ingredients (API). While the current scope of this problem is unknown, the World Health Organization estimates that 10% of the pharmaceuticals in the global supply chain are counterfeit. In addition to the health and safety concerns that counterfeits pose, pharmaceutical companies worldwide lose billions of dollars in revenue to counterfeit drugs. Popular, widely used medications are a common target for criminal organizations who typically sell these products over the internet. Counterfeit targets not only include lifestyle drugs (non-life-threatening conditions such as weightloss or impotence) but recently also has included lifesaving treatments such as antimalarial or even anti-cancer medication(1).
Instrument miniaturization has led to out-of-laboratory analysis for pharmaceutical and other product authentication. Raman spectroscopy is ideal for pharmaceutical identification due to its chemical selectivity and it is known to detect counterfeit drugs(2). Portable Raman instruments equipped with laser excitation at 785nm are widely available. However, there still remains a challenge with overcoming fluorescence interference seen in many pharmaceutical materials analyzed using 785nm excitation. This current study compares a Xantus®-2 portable Raman equipped 1064nm laser (Rigaku RamanTechnologies) against a competitive system equipped with a 785nm laser.
Instrument and Measurement Conditions
Samples were analyzed with data recorded either using a Rigaku Xantus®-2 Dual
instrument (Micro 2020® software, version 18.104.22.168) or a competitive system equipped with a 785 nm laser. In all cases, a laser power of 300mW, with auto-exposure was employed in (exposure times were typically 1000ms).
Sample Preparation and Analysis
Samples of authentic and counterfeit tablets and capsule types were used, including
Alli® (Orlistat) and Viagra® (Sildenafil Citrate). Alli® capsule blends were emptied into a vial and then measured directly using Rigaku Xantus®-2 Raman (1064nm Laser) and the competitive system at 785nm excitation. Viagra® tablets were measured “as is” through the coating on both instruments.
Figure 1: Rigaku’s Xantus®-2-785/1064 Dual Wavelength Spectrometer with Sample Vial Holder.
All spectra were viewed in the optimal finger print region of 300 to 1650 cm-1. In all cases, excitation at 785nm yielded a strong fluorescence background precluding comparison of authentic and counterfeit products. Fluorescence interference was not seen with 1064nm excitation.
Utility of the Xantus®-2 Raman (1064nm laser) can be seen in Figure 2. Fluorescence interference obscures all usable spectral information when 785nm excitation is used while spectra obtained at 1064nm easily distinguish between authentic and counterfeit Alli® products.
Figure 3 shows authentic Viagra measured at both 785 and 1064nm excitation. Titanium dioxide bands from the authentic and counterfeit Viagra® samples were visible at 785nm excitation, superimposed over a broad fluorescence background. Only 1064nm excitation clearly distinguishes between authentic and counterfeit products.
Spectral information from the tablet coating material, Opadry Blue as well as the API, Sildenafil Citrate, can be seen in Raman spectra obtained from the coated Viagra® sample, Figure 3. By comparing the spectra obtained from the coated tablet with those from core of the tablet and pure Opadry Blue, it is clear that the 1064nm excitation Raman can measure the tablet core through the coating. The bands marked with the * were identified as belonging to the API by comparison with pure Sildenafil Citrate (data not shown). This degree of identifying information was not observable in data obtained using 785nm excitation.
In many cases, Raman excitation at 785nm yields fluorescence interference that can preclude the use of Raman as an investigative tool for counterfeit detection. Raman data acquired using 1064nm excitation can provide fluorescence free, chemically specific data.
(1) M. Mathlouthi, D. V. Luu in Carbohydrate Research, Vol. 78, 1980, pp. 225.
(2) W. Szarek, S. Korppi-Tommola, H. Shurvell, V. Smith, O. Martin in Canadian Journal of Chemistry, Vol. 62, 1984, pp. 1612. Alli® is a registered trademark of GlaxoSmithKline and Viagra® is a registered trademark of Pfizer.
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