More common, GC/MS drug testing procedure separates drugs based on how easy they evaporate (volatilize). Unfortunately some substances, such as drugs of abuse, do not volatilize. On the other hand, LC/MS analysis for drugs separates substances and introduces them into the mass spectrometer. The sample first passes through a mass filter which allows only the drugs we are testing for to pass through. The drug is then broken apart with an argon gas stream. The fragments of any drug present then pass into a second mass filter and are then measured. Only when drugs of abuse are present, are compounds noted by the instrument.
The results are virtually 100% accurate.