Surface Sampling and Optimization of Desorption Electrospray Ionization by Spray Desorption Collection
Analysis of chemicals on the surface with mass spectrometric techniques were revolutionized after desorption electrospray ionization (DESI) mass spectrometry was introduced in 2004. Here, development of a surface sampling technique based on DESI is reported. This technique decouples desorption and ionization, two processes that occur simultaneously in DESI. Desorbed chemicals from a surface are collected on a secondary collection surface which can be analyzed independently. This technique called spray desorption collection (SDC) is evaluated here. It shows great potential for pre-concentration of trace compounds from solid surfaces as it is found that the amount of collected material increases linearly with the area from which it was collected. The geometry of SDC was improved and its application for collecting agrichemicals and pharmaceuticals from different surfaces were evaluated. In another application SDC was combined with solid phase microextraction (SPME) fibers to sample compounds across a broad volatility range. The results for SDC-SPME for trap grease is compared with those obtained with headspace SPME. Finally SDC is also used to study the desorption mechanism of DESI. Another technique called reflective ESI is introduced and these two techniques together show that the optimized conditions for DESI is a compromise between those that effect efficient desorption and efficient ionization. This work represents the introductory research on SDC.