Development and implementation of a pass/fail field-friendly method for detecting sildenafil in suspect pharmaceutical tablets using a handheld Raman spectrometer and silver colloids

• Published in: Journal of pharmaceutical and biomedical analysis 2017-11, Vol.146, p.420-425
• Main Authors: Lanzarotta, Adam, Lorenz, Lisa, Batson, JaCinta S., Flurer, Cheryl
• Format: Article
• Language: English
• Subjects: Chemistry, Pharmaceutical - methods; Counterfeit; Handheld Raman; Pass/Fail; SERS; Sildenafil; Sildenafil Citrate - chemistry; Silver - chemistry; Solubility; Spectrum Analysis, Raman - methods; Surface enhanced Raman spectroscopy; Tablets - analysis; Tablets - chemistry
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/j.jpba.2017.09.005

[Display omitted] •Handheld Raman spectrometers and silver colloids are used to detect sildenafil in suspect tablets.•The method is based on a pass/fail platform that can be taught to non-experts in about 20min.•The method involves measuring sample solutions directly through glass vials (no drying required).•The method proved to be 92.6% effective on average for 117 counterfeit and unapproved drugs.•The method yielded detection limits in samples as low as 10ppm. A simple, fast, sensitive and effective pass/fail field-friendly method has been developed for detecting sildenafil in suspect Viagra and unapproved tablets using handheld Raman spectrometers and silver colloids. The method involves dissolving a portion of a tablet in water followed by filtration and addition of silver colloids, resulting in a solution that can be measured directly through a glass vial. Over one hundred counterfeit Viagra and unapproved tablets were examined on three different devices during the method development phase of the study. While the pass/fail approach was found to be 92.6% effective on average, the efficacy increased to 97.4% on average when coupled with the software’s “Discover Mode” feature that allows the user to compare a suspect spectrum to that of a stored sildenafil spectrum. The lowest concentration of sildenafil in a water/colloid solution that yielded a “Pass” was found to be 7.6μg/mL or 7.6 parts per million (ppm). For the analysis of suspect tablets, this value was found to be as low as 10μg/mL and as high as 625μg/mL. This variability was likely related to the tablet formulation, e.g., concentration of sildenafil, presence and concentration of water-soluble and/or water-insoluble ingredients. However, since most counterfeit Viagra and unapproved tablets contain >50mg sildenafil per tablet, such low concentrations will not be encountered often. Limited in-lab and in-field validation studies were conducted in which analysts/field agents followed the procedure outlined in this study for small sample sets. These individuals were provided with written instructions, a ∼20min demonstration regarding how to perform the procedure and use the instrument, and a kit with field-friendly supplies (purified bottled water from a local grocery store, disposable plastic pipettes, eye-dropper with a silver colloid solution, etc.). The method proved to be 98.3% and 91.7% effective for the in-lab and in-field validation studies, respectively, which demonstrated the ruggedness, s