Screening for total ergot alkaloids in rye flour by planar solid phase extraction-fluorescence detection and mass spectrometry

The analysis of ergot alkaloids is generally performed by high-performance liquid chromatography (HPLC) coupled to fluorescence detection (FLD) or mass selective detection. As for monitoring only the sum of ergot alkaloids is relevant, a fast and easy screening method for the determination of the total alkaloid content was developed using planar solid phase extraction (pSPE). Applying pSPE, recently introduced for pesticide residue analysis in fruits and vegetables (Oellig and Schwack, 2011) and tea (Oellig and Schwack, 2012), all ergot alkaloids are concentrated in a target zone followed by detection as the sum. The herein presented method includes an ammonium acetate buffered extraction step, followed by a fast liquid-liquid partitioning pre-cleaning before pSPE is performed on high-performance thin-layer chromatography (HPTLC) amino plates with a single methanol development to separate the ergot alkaloids from the remaining matrix and to collect them in a single zone. For quantitation, the native fluorescence was used after dipping the plate in n-hexane/paraffin solution for fluorescence enhancement. Limits of detection and quantitation of 0.07 and 0.24 mg/kg rye, respectively, expressed as ergocristine, were well below the currently applied quality criterion limit for rye. Near-100% recoveries were obtained at relevant spiking levels for different rye flour samples. Hence, the fast pSPE-FLD is an efficient and reliable method to screen for the total ergot alkaloid content in rye and a rapid alternative to the HPLC determination of individual alkaloids and to summing them up. HPTLC-MS additionally enables the identification of the ergot alkaloid composition by a single mass spectrum, when utilized as a fingerprint, offering an easy differentiation of Secale cornutum from different origins.