Transfer of silica gel TLC screening methods for clarithromycin, azithromycin, and amodiaquine + artesunate to HPTLC–densitometry with detection by reagentless thermochemical activation of fluorescence quenching

ABSTRACT

A previously published model process was used for the transfer of silica gel thin-layer chromatography (TLC) screening methods for clarithromycin, azithromycin, and amodiaquine + artesunate pharmaceutical formulations published in the Global Pharma Health Fund E.V. Minilab manual for the identification of counterfeit drugs to high-performance TLC–densitometry quantitative methods that can be used in support of regulatory compliance actions. In these new methods, detection of clarithromycin, azithromycin, and artesunate was achieved by thermochemical activation involving simple reagent-free heating of the layer to produce derivatives of the drugs that quench fluorescence under 254 nm ultraviolet light. Additional drugs with TLC screening methods published in the Minilab manual and/or Compendium of Unofficial Methods for Rapid Screening of Pharmaceuticals by Thin Layer Chromatography that do not naturally quench fluorescence were studied and also found to be detectable by thermochemical activation on silica gel layers. The conditions of the thermochemical activation were studied, and in situ spectra of drug zones before and after heating were obtained. Heat activation of fluorescence quenching seems to be a widely applicable detection method that is safer and more convenient than the use of chemical spray, dip, or vapor phase reagents.

GRAPHICAL ABSTRACT

KEYWORDS:

• Amodiaquine
• artesunate
• azithromycin
• clarithromycin
• thermochemical activation
• thin-layer chromatography

Acknowledgments

The authors thank Thomas Layloff, Senior Quality Assurance Advisor, supply chain management system (SCMS), Arlington VA, USA, for his support of this research, reviewing the manuscript prior to its submission for publication, and arranging for delivery of the azithromycin and amodiaquine + artesunate pharmaceutical products supplied by the Dar es Salaam, Tanzania, Office of SCMS. Danhui Zhang supplied the clarithromycin pharmaceutical product. We also thank EMD Millipore Corp. for providing the premium purity glass HPTLC plates used in our experiments. Ellen Armour was supported by a Camille and Henry Dreyfus Foundation Senior Scientist Mentor Program award to Professor Joseph Sherma.