Solid Phase Microextraction–Multicapillary Column–Ion Mobility Spectrometry (SPME–MCC–IMS) for Detection of Methyl Salicylate in Tomato Leaves

Methyl salicylate (MeSA) is a plant-signaling molecule that plays an essential role in the regulation of plant responses to biotic and abiotic pathogens. In this work, solid phase microextraction (SPME) and a multicapillary column (MCC) are coupled to ion mobility spectrometry (IMS) to detect MeSA in tomato leaves. The SPME-MCC-IMS method provides two-dimensional (2D) separation by both MCC and IMS, based on the retention and drift times. The effect of the IMS polarity on the separation efficiency of MCCs was also investigated. In the positive polarity, ionization of MeSA resulted in [MeSA + H]+ formation while, in the negative, deprotonated ions, [MeSA - H]-, and the O2- adduct ion, [MeSA + O2]-, were formed. In the real sample analysis, the negative polarity operation resulted in the suppression of many matrix molecules and thus in the reduction of interferences. Four different SPME fibers were used for head space analysis, and four MCC columns were investigated. In the negative polarity, complete separation was achieved for all of the MCCs columns. The limits of detection (LODs) of 0.1 μg mL-1 and linear range of 0.25-12 μg mL-1 were obtained for the measurement of MeSA in a standard solution (H2O/CH3OH, 50:50) by the SPME-IMS method with a 5 min extraction time using an SPME with a PDMS fiber, in the negative mode of IMS. The MeSA contents of fresh tomato leaves were determined as 1.5-9.8 μg g-1, 24-96 h after inoculation by tomato mosaic ringspot virus (ToRSV).