Development of an On-plate Sample Pretreatment for MALDI-TOF-MS Measurements and Its Application to the Analysis of Organic Industrial Products

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has been used as a powerful tool for the structural characterization of polymeric materials. However, the presence of components having a highly ionization efficiency, such as polyethyleneoxide (PEO)-type surfactants, significantly suppresses the ionization of interesting target compounds in the sample. This study was proposed a simple sample pretreatment to selectively remove PEO components from the surface on the sample/matrix co-crystal. In this procedure, PEO components can be washed away by adding and aspirating an aliquot of aqueous methanol. A key point of this procedure is the use of water-insoluble matrix reagents, such as 2,4,6-trihydroxyacetophenone (THAP), which can retain the sample/matrix co-crystal during the removal procedures. This technique was first applied for characterizing the composition of a commercial shampoo. By removing sodium laureth sulfate (SLS), which is a typical PEO-type anionic surfactant, many mass spectral peaks suppressed by SLSs could be observed. After conversion of the mass spectral data to a Kendrick mass defect (KMD) plot, the compositional distribution of various PEO-type non-ionic surfactants and PEO hydrogenated castor oil could be depicted. An urethane/acrylate-based UV-curable coating material was then characterized. By removing PEO-type nonionic surfactants, it could be speculated that the remaining components contained isophorone diisocyanate (IPDI) and pentaerythritol (di/tri) acrylate units. This method will be a useful sample-pretreatment technique for screening formulation information concerning industrial polymeric materials.