Effects of Heat Treatment on Anodic Porous Alumina Membranes for Mass Spectrometry

Desorption ionization using through-hole alumina membrane (DIUTHAME) method is a mass spectrometry imaging (MSI) method that uses an anodic porous alumina membrane (APAM) with an array of submicron-sized through-holes as a surface-assisted laser desorption/ionization (SALDI) substrate. The DIUTHAME method is particularly promising for MSI because it does not generate interfering peaks in the low-molecular-weight region. However, the SALDI effect cannot be obtained if the nanostructures of the substrate are destroyed owing to laser irradiation before sample vaporization. APAMs that maintain their structures after irradiation with a high-intensity laser must be fabricated to realize highly sensitive measurements. In this study, we investigated the role of heat treatment suppressing the laser irradiation induced fracture of APAMs. We found that heat treatment at higher temperatures more effectively suppressed APAM fracture associated with laser irradiation. This result was attributed to the reduction of anion-derived impurities in APAMs upon heat treatment. The resulting heat-treated APAM is expected to serve as a substrate for highly sensitive and robust MSI.