Stephen Ritter's excellent article "The Dope on Testosterone Tests" thoroughly described the natural product chemistry, analytical chemistry, and other related issues in the Floyd Landis Tour de France scandal (C&EN, Aug. 28, page 43). Such clarity has not been present in other magazine or newspaper accounts. The discussion of the confirmatory stable carbon isotope ratio analysis (SCIRA) test was of particular interest.
About 25 years ago, my colleagues and I developed SCIRA methods to detect widespread undeclared addition of inexpensive sweeteners from the C4 plants corn and sugarcane to the more expensive honey and fruit juices from C3 sources. It wasn't long before unscrupulous processors began tailoring adulterants so that their 13C/12C signatures matched those of the food, thereby allowing adulterated mixtures to go undetected. One hopes that C4 plant sources of the diosgenin and stigmasterol precursors to testosterone are not being used in combination with their C3 sources, such as soybean oil, in order to match the 13C/12C ratios of testosterone synthesized in humans.