Onsite detection of ephedrine in slimming aids by TLC-SERS

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  • Published: Feb 24, 2015
  • Author: Steve Down
  • Channels: HPLC / Raman

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Undeclared and illegal additives are often added to dietary slimming aids to give them more apparent potency but the perpetrators take no account of any potential ill effects that these might bring to their customers. Such is the case with ephedrine and its analogues like pseudoephedrine, norephedrine and methylephedrine, which are commonly found in this context, even though they were banned by the FDA in 2004. Their unregulated consumption can lead to cardiovascular problems, increased blood pressure and other unpleasant side effects.

Several methods for detecting ephedrine analogues have been published but Chinese researchers have developed a rapid procedure which is suitable for onsite deployment, so could be taken inside manufacturing and distribution facilities to test the products held there. Described in Analytical and Bioanalytical Chemistry, the new method use thin-layer chromatography combined with surface-enhanced Raman spectroscopy.

The ephedrines were extracted from slimming aids and separated on the TLC plate before being stained with a silver colloid which marked the spots for SERS analysis. The four compounds were nicely separated and their characteristic Raman peaks identified the individual compounds and distinguished them from each other. The detection limit of 10 ppm is not particularly impressive but it is sufficient for the levels in slimming supplements that might cause health problems to consumers.

One key advantage is the speed of the analysis. Once the TLC separation is complete SERS analysis takes a mere 5-10 s. This speed combined with the portability of some types of modern Raman spectrometer suggests that it would be a ideal method for on-the-spot testing of products.

What the method does not do is measure the amount of ephedrine analogue in a product but its presence is sufficient to confirm illegality, so this is not of paramount importance. In theory, it could be extended to other ephedrine analogues but their separation and Raman spectra would need to be confirmed before they can be integrated into the method.


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