A portable system 10 is disclosed for collecting a sample from exhaled breath of a subject. Drug substance in the exhaled breath are detected or determined. The sample is collected for further analysis using mass-spectroscopy. The system comprises a sampling unit 14 and a housing 12 arranged to hold the sampling unit 14, the sampling unit 14 is adapted to collect non-volatile and volatile compounds of the at least one drug substance from the exhaled breath from the subject. The housing 12 has at least one inlet 15 for the subject to exhale into the housing 12 to the sampling unit 14 and at least one outlet 16 for the exhaled breath to exit through.
