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).