Sample Prep for Trace Analysis of Adulterants in Erectile Dysfunction Dietary Supplements

Significance of the Topic

The global market of dietary supplements is expanding rapidly, raising concerns about product authenticity and consumer safety due to adulteration with pharmaceutical compounds. Erectile dysfunction supplements have been frequently spiked with PDE-5 inhibitors such as sildenafil and tadalafil, underscoring the need for sensitive and selective analytical methods to detect trace adulterants. Efficient sample preparation is crucial to minimize matrix effects and instrument contamination while enabling reliable quantitation of low-level adulterants.

Objectives and Overview of the Study

This study compares two sample preparation strategies for trace analysis of PDE-5 inhibitors and related compounds in single- and multi-ingredient erectile dysfunction dietary supplements. The goals are to evaluate a modified QuEChERS approach and a cartridge-based Weak Cation Exchange SPE (Agilent Bond Elut Plexa PCX) in terms of analyte recovery, reproducibility, and cleanup efficiency, using LC/MS/MS detection.

Methodology and Instrumentation

• Sample homogenization: Tablets and capsules were ground to a homogeneous powder.
• Modified QuEChERS: 1 g sample extracted with 10 mL 80 % methanol, dispersive cleanup with graphitized carbon black, C18, and MgSO₄.
• SPE (Plexa PCX): Extraction in 80 % methanol followed by dilution in 2 % phosphoric acid, loading onto PCX cartridges, washing with acidic aqueous solution, and elution with ammonia in organic solvent.
• Chromatography and detection: Agilent 1290 Infinity LC with Poroshell C18 columns, gradient elution (10–80 % methanol with 0.1 % formic acid), and Agilent 6410 Triple Quadrupole MS operating in MRM mode.

Main Results and Discussion

QuEChERS delivered acceptable recoveries (58–127 %) and RSDs for single-ingredient ginseng matrices but failed to detect analytes in complex formulations. The Plexa PCX SPE method provided cleaner extracts and consistent recoveries (76–87 % for most analytes) with RSDs below 7 %, except for icariin in highly complex samples. Chromatograms showed significant baseline noise reduction and improved peak shapes after SPE cleanup.

Benefits and Practical Applications of the Method

The optimized SPE workflow enhances sensitivity and selectivity for trace-level screening of adulterants in dietary supplements, facilitating regulatory compliance with cGMP guidelines. It supports high-throughput testing in quality control laboratories and can be adapted to various supplement matrices and a growing list of pharmaceutical adulterants.

Future Trends and Potential Applications

Emerging trends include automation of sample preparation, development of novel sorbents for broader analyte coverage, integration with high-resolution mass spectrometry for non-target screening, and application of chemometric tools and machine learning for pattern recognition of complex adulteration profiles.

Conclusion

This work demonstrates that cartridge-based ion-exchange SPE provides superior cleanup and reliable quantitation of PDE-5 inhibitors in complex dietary supplements compared to modified QuEChERS. The approach can be tailored to future analyte panels and diverse supplement formulations to ensure product integrity.

Used Instrumentation

• Agilent 1290 Infinity LC System
• Agilent 6410 Triple Quadrupole Mass Spectrometer
• Poroshell 120 EC-C18 columns

References

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4. F. Song et al., J. Pharm. Biomed. Anal. 70, 40 (2012).