On your marks

Counterfeiters have wised up to the fact that petrochemicals manufacturers
add secret markers to prove that a petrol mixture is the genuine article. The
crooks analyse the marker and add it to their inferior or diluted product. Now
Biocode of Cambridge, Massachusetts, has a way to fight back (W0 98/33162).
Traces of coloured or fluorescent marker chemicals are added, but in such small
concentrations that they are undetectable. To prove that a product is genuine,
the substance must be precipitated to increase its concentration 10 000-fold. It
then becomes detectable. The counterfeiter will not know what the hidden marker
is, or how to precipitate it.