An automatic versatile system integrating solid-phase extraction with ultra-high performance liquid chromatography–tandem mass spectrometry using a dual-dilution strategy for direct analysis of auxins in plant extracts

• An automatic versatile SPE-UHPLC–MS/MS system was developed.
• The online system was realized by a dual-dilution strategy.
• A post-column compensation mode for the matrix-effects evaluation was designed.
• System feasibility was demonstrated by the analysis of 3 auxins from plant tissues.

An automatic versatile system which integrated solid phase extraction (SPE) with ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) was developed. Diverse commercial SPE columns can be used under an ambient pressure in this online system realized by a dual-dilution strategy. The first dilution enabled the direct injection of complex samples with minimal pretreatment, and the second dilution realized direct introduction of large volume of strong eluent into the UHPLC column without causing peak broadening or distortion. In addition, a post-column compensation mode was also designed for the matrix-effects evaluation. The features of the online system were systematically investigated, including the dilution effect, the capture of desorption solution, the column-head stacking effect and the system recovery. Compared with the offline UHPLC system, this online system showed significant advantages such as larger injection volume, higher sensitivity, shorter analysis time and better repeatability. The feasibility of the system was demonstrated by the direct analysis of three auxins from different plant tissues, including leaves of Dracaena sanderiana, buds and petals of Bauhinia. Under the optimized conditions, the whole analysis procedure took only 7 min. All the correlation coefficients were greater than 0.9987, the limits of detection and the limits of quantitation were in the range of 0.560–0.800 ng/g and 1.80–2.60 ng/g, respectively. The recoveries of the real samples ranged from 61.0 to 117%. Finally, the post-column compensation mode was applied and no matrix-effects were observed under the analysis conditions. The automatic versatile system was rapid, sensitive and reliable. We expect this system could be extended to other target analytes in complex samples utilizing diverse SPE columns.