Sandpaper: Efficient Medium for Analysis of Polishable Solid Samples by Ambient Mass Spectrometry

In this paper, we employed sandpaper as an efficient medium to analyze polishable solid samples. As proof of principle, the surfaces of coffee beans were sanded with pieces of sandpaper cut into a triangular shape. The triangle was placed in front of the mass spectrometer inlet, and methanol was dropped on its surface. After a high-voltage application, the fingerprints of the coffee beans (n = 100) were achieved in the positive and negative ion modes in an identical procedure employed for paper spray mass spectrometry (PS-MS) analysis. The new methodology, named sandpaper spray mass spectrometry (SPS-MS), allowed for identifying many compounds in coffee beans, mainly caffeine, sugars, and carboxylic acids, among other molecules. The new technique shows advantages over PS-MS in analyzing polishable solid samples. Furthermore, compared to the direct analysis of tissues such as leaves, grains, and seeds, in which the pieces must be cut in a triangular shape (a difficult task depending on the samples' hardness), the SPS-MS technique is much more straightforward. Finally, SPS-MS can be potentially applied to analyze other hard surfaces such as wood, plastic, and assorted crop grains.