The researchers used water and an ultrasonic extraction process, followed by gas chromatography-mass spectrometry to quantify the amount of cocaine in more than 230 bills collected in 17 cities.

To do this, the oils were broken into their component parts and analysed using gas chromatography and mass spectrometry.

Scientists had to wait until the development of a technique called gas chromatography/mass spectrometry to identify traces of methoxypyrazines.