Determination of Phosphodiesterase Type-5 Inhibitors (PDE-5) in Dietary Supplements

Abstract

This study proposed a high-performance thin-layer chromatography (HPTLC) screening method to detect phosphodiesterase 5 (PDE-5) inhibitors as possible adulterant agents in various dietary supplements. Chromatographic analysis was performed on silica gel 60F254 plates using a mixture of ethyl acetate:toluene:methanol:ammonia in a volume ratio of 50:30:20:0.5 as a mobile phase. The system provided compact spots and symmetrical peaks of sildenafil and tadalafil with retardation factor values of 0.55 and 0.90, respectively. The analysis of products purchased from the internet or specialized stores demonstrated the presence of sildenafil, tadalafil, or both compounds in 73.3% of products, highlighting inadequacies and inconsistencies in the labeling, as all dietary supplements were declared to be natural. The results were confirmed using ultra-high-performance liquid chromatography coupled with a positive electrospray ionization high-resolution tandem mass spectrometry (UHPLC-HRMS-MS) method. Furthermore, in some samples, vardenafil and various analogs of PDE-5 inhibitors were detected using a non-target HRMS-MS approach. The results of the quantitative analysis revealed similar findings between the two methods, with adulterant quantities found to be similar to or higher than those in approved medicinal products. This study demonstrated that the HPTLC method is a suitable and economical method for screening PDE-5 inhibitors as adulterants in dietary supplements intended for sexual activity enhancement.

Keywords: HPTLC; UHPLC-HRMS-MS; adulterants; dietary supplements; sildenafil; tadalafil.

Figure 1

Sildenafil.

Figure 2

Tadalafil.

Figure 3

Vardenafil.

Figure 4

Three-dimensional chromatogram for sildenafil (standard), tadalafil (standard), and samples 1, 2, and 3 (detection at λ = 254 nm; samples 1, 2, and 3 were positive for sildenafil).

Figure 5

Three-dimensional chromatograms for sildenafil (standard), tadalafil (standard), and samples 10, 11, and 12 (detection at λ = 254 nm; samples 10 and 11 were positive for sildenafil and tadalafil, respectively; sample 12 was negative).

Figure 6

In situ absorbance–reflectance UV spectra of sildenafil standards and samples 1, 2, and 3.

Figure 7

In situ absorbance–reflectance UV spectra of caffeine in sample 5 (Rf = 0.78).

Figure 8

In situ absorbance–reflectance UV spectra of tadalafil standards and sample 11.

Figure 9

Sildenafil identification in sample 10 (MS-MS).

Figure 10

Caffeine identification in sample 4 (MS-MS).

Figure 11

Chromatogram of sample 6: TIC (total ion current) and identification of sildenafil, tadalafil, avanafil, pseudovardenafil, and vardenafil oxopiperazine.