Detection of sildenafil adulterated in herbal products using thin layer chromatography combined with surface enhanced Raman spectroscopy: “Double coffee-ring effect” based enhancement

• Published in: Journal of pharmaceutical and biomedical analysis 2019-09, Vol.174, p.340-347
• Main Authors: Minh, Dao Thi Cam, Thi, Le Anh, Huyen, Nguyen Thi Thanh, Van Vu, Le, Anh, Nguyen Thi Kieu, Ha, Pham Thi Thanh
• Format: Article
• Language: English
• Subjects: Adulteration; Chromatography, Thin Layer - methods; Colloids - chemistry; CRE; Drug Contamination; Herbal; Limit of Detection; Metal Nanoparticles - chemistry; Plant Preparations - analysis; SERS; Sildenafil; Sildenafil Citrate - analysis; Silver - chemistry; Spectrum Analysis, Raman - methods; Tandem Mass Spectrometry; TLC; Vietnam
• ISSN: 0731-7085; 1873-264X
• DOI: 10.1016/j.jpba.2019.05.043

[Display omitted] •A TLC-SERS method was developed for detection of sildenafil adulteration in herbal products collected from local market.•A novel “double coffee-ring effect” resulted in significant improvement of TLC-SERS performance of the method.•Sildenafil adulteration was detected by the DCRE-TLC-SERS method, with results confirmed by LC–MS/MS analyses. Sildenafil is an inhibitor of the phosphodiesterase type 5 which is commonly adulterated in herbal health products. In this study, a rapid, sensitive and selective method using thin layer chromatography (TLC) combined with surface-enhanced Raman spectroscopy (SERS) was developed for identification of sildenafil adulteration in herbal drugs and dietary supplements. TLC separation method was developed and different SERS factors were investigated: nanosilver colloid preparation, concentration and volume, and coffee-ring effect (CRE) enhancement for SERS measurement. “Double CRE” - a newly observed effect that resulted in the redistribution of both silver nanoparticles and sildenafil molecules – was reported for the first time in TLC-SERS applications. This method presented an efficient TLC-SERS performance enhanced by the “hot spots” obtained under double CRE. The method was validated in terms of selectivity on three blank matrixes (capsule, granule, and herbal extract) and sensitivity with a limitation of detection (LOD) of 2 ng/spot for sildenafil. The validated method was implemented on 9 herbal products sold on the market as erectile dysfunction therapy. Two products were detected with sildenafil adulteration by the TLC-SERS method and confirmed by parallel LC–MS/MS analysis. These results exhibited the reliability and feasibility of the developed method in adulteration screening for sildenafil. On the other hand, the novel findings on double CRE provided extra information for CRE optimization in TLC-SERS applications.