Extracts taken from spent growth media from Pseudomonas aeruginosa can be analyzed for N-acyl-L-homoserine lactones and 2-alkyl-4-(1H)-quinolones (AQs), including the known quorum sensing signalling molecules of P. aeruginosa, in a specific and sensitive manner by liquid chromatography coupled with tandem mass spectrometric detection. This analysis can be conducted in a quantitative manner by comparison with matrix-matched calibration samples.