METHODOLOGY FOR DETECTION AND STRUCTURAL CHARACTERIZATION OF PHOSPHODIESTERASE-5 (PDE-5) INHIBITOR ADULTERANTS IN AN HERBAL COFFEE

Importance of the Topic

Functional beverages marketed as herbal remedies for erectile health have gained popularity, but undisclosed synthetic additives like PDE-5 inhibitors carry significant health risks and regulatory concerns.

Objectives and Study Overview

The study establishes a multi-tiered analytical workflow to screen for and characterize known and unknown phosphodiesterase-5 inhibitor adulterants in herbal coffee products, combining rapid direct analysis and detailed structural identification.

Methodology

A two-sample set of herbal coffee sachets was first screened using direct analysis in real time (DART) coupled to a single quadrupole mass detector (ACQUITY QDa) under positive ionization at 400 °C. Suspect signals were confirmed with UPLC-PDA-HRMS (Xevo G2-XS QTof) following an acetonitrile/water extraction of 12.5 g sample. Data-independent acquisition (MSE) captured precursor and fragment spectra. Unknown analogues were isolated via preparative supercritical fluid chromatography for NMR characterization.

Used Instrumentation

• DART interface with ACQUITY QDa single quadrupole (m/z 90–600, cone voltages 15–80 V)
• ACQUITY H-Class UPLC with CORTECS C18 column (2.1 × 100 mm, 1.6 µm)
• Xevo G2-XS QTof high-resolution MS in positive ESI, MSE mode
• Preparative SFC system for analogue isolation
• 1H and 13C NMR spectroscopy for structural elucidation

Main Results and Discussion

DART-QDa screening rapidly detected signals corresponding to caffeine, sildenafil, and tadalafil in one sample, and an unknown peak at m/z 505 in another. UPLC-PDA-HRMS confirmed the known inhibitors via accurate mass and fragmentation patterns, and database matching in UNIFI linked the unknown analogue to thiohomosildenafil. Isolation by SFC yielded sufficient purity for NMR, which supported the proposed structure despite broadened piperazine resonances. Quantification using UV absorbance at 220 nm indicated approximately 60 mg of the analogue per sachet, equivalent to a therapeutic dose.

Benefits and Practical Applications

The presented approach combines speed and specificity, enabling on-site rapid screening of herbal products without extensive sample prep, followed by robust confirmation and structural elucidation. This workflow enhances consumer safety monitoring and aids regulatory compliance.

Future Trends and Applications

Integration of ambient ionization with real-time data-driven libraries and machine learning could further accelerate detection of emerging adulterants. Expanding spectral databases and coupling with portable HRMS may support field testing of functional foods.

Conclusion

The multi-modal analytical strategy effectively identified both known and novel PDE-5 inhibitor adulterants in herbal coffee, demonstrating its utility for safeguarding public health and quality control.

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