Development of a liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI MS/MS) method for the quantification of bioactive substances present in olive oil mill wastewaters

A novel liquid chromatography–electrospray ionization-tandem mass spectrometry (LC–ESI MS/MS) method was developed and validated for the simultaneous determination of the bioactive substances hydroxytyrosol, tyrosol and 2-(5-ethylidene-2-oxo-tetrahydro-2H-pyran-4-yl)acetic acid in olive oil mill wastewater samples (OMW). The chromatographic separation was performed on a RP-C8 column using a water–acetonitrile gradient program and the detection was achieved by tandem MS in the negative ion mode. Calibration curves were linear for all bioactive compounds over the range of 1–100 ng injected, while the method exhibited good accuracy, intra- and inter-day precision. The limit of detection and the limit of quantification were in the low to mid pg range and the method was simple and rapid. Because the disposal of OMW is an environmental problem and on the other hand OMW are rich in biologically active compounds that could be recovered and exploited in various applications, the developed method was applied to the monitoring of OMW samples and the quantitative determination of the aforementioned substances. In this way, the original content in bioactive compounds could be assigned in the raw matrix, and the enrichment of the samples by various pretreatment methods could be assessed. Also, full-scan ESI MS was applied to OMW samples for the identification of several compounds known to be present in OMW.