Fast Detection of Sucrose Esters in Tobacco Leaf Using Liquid Chromatography Coupled with Ion Mobility-Quadrupole/Time of Flight Mass Spectrometry

Ion mobility spectrometry combined with mass spectrometry (IM-MS) has grown in popularity as a powerful analytical technique. IM is capable of separating ionized molecules in the gas phase based on their mobility in a carrier buffer gas, whereas MS is effective to measure the weight of these ions. It brings a two-dimensional correlation spectrum to obtain the relationship between the ratios of shape-to-charge from IM and the ratios of mass-to-charge (m/z) from MS. The ability to analyze a wide range of compounds makes IM-MS a valuable tool for an analytical research laboratory, which is often used to perform difficult qualitation that are not possible by other methods. Sucrose esters (SEs), as one of the major chemical compositions of tobacco leaves, are generated from one or more hydroxyl sucroses esterified with fatty acids. Research on SEs is paid more attention because of its responsibility for tobacco flavor. More than this, they are considered to be important in plant or insect interactions and possess both antibiotic and plant-growth regulating activities. Due to the complexity of esterification, the number and position of the acetyl groups in SE varies, there are a few of studies about the analysis of SEs that have been reported using GC/MS or LC/MS. But it is still difficult to characterize their structures in lack of the standard references. So it is valuable to improve the qualitative analysis of SEs in tobacco leaves. In this work, SEs in tobacco leaves were fast detected by liquid chromatography coupled with ion mobility-quadrupole/time of flight tandem mass spectrometry (LC-IM-Q TOF MS). The experiment was performed using an eluent of 0.1% formic acid in methanol-water (80∶20, V/V), and the electrospray ionization technique in positive ion mode was adopted. The sodium added quasi molecular ions of SEs from the extract of tobacco leaves were formed, separated in the ion mobility drift tube, and eventually detected by quadrupole/time-of-flight tandem mass spectrometry. As a result, six kinds of SEs were detected, with the difference of 0.2-0.8 min in LC retention time, the difference of 0.4-0.5 ms in IM drift time, and the difference of 14 u in MS ion mass. Furthermore, the SEs were identified using a multidimensional qualitative analysis approach consisting of MS/MS spectra, measurement of elemental composition for quasi molecular ion, and the calculation of CCS. In conclusion, LC-IM-Q TOF MS was proved to be one of the most efficient tools for the fast detection of SEs in complex matrices. It could improve the accuracy of qualitative analysis when coupled with the multidimensional qualitative approach.