Detection of Plasticizers in Soil Using Surface Desorption Atmospheric Pressure Chemical Ionization Imaging Mass Spectrometry

To address the widespread contamination of surface soil by phthalate esters (PAEs), a method based on the surface desorption atmospheric pressure chemical ionization tandem mass spectrometry (SDAPCI-MSn) imaging technology was successfully applied for the direct determination of diethyl phthalate (DEP) in soil without any pretreatment. The precursor ion, protonated diethyl phthalate (m/z 223), was confirmed by collision-induced dissociation (CID) experiments to exclude false-positive results. The protonated DEP (m/z 223) and the characteristic fragment (m/z 177) were used to obtain the distribution of DEP molecules in the soil using imaging mass spectrometry. The two ion images without any pretreatment showed that the distribution of DEP was inhomogeneous in the shape of clusters, but these two distributions were changed after adding deionized water evenly into the surface of soil. The spatial resolution and the analysis speed per pixel were 0.25 mm2 and 4.5 s. This new method may be applicable for the study of content and distribution of PAEs in other complex solid samples.

Surface desorption atmospheric pressure chemical ionization (SDAPCI) utilizes corona discharge to transfer energy and charge to the carriers (e.g., water molecules) at atmospheric pressure. A high voltage was applied to a stainless needle to produce primary ions. Under the influence of the electric field, the charged species directly impact sample surface to produce analyte ions for mass analysis.Figure optionsDownload as PowerPoint slide