Ion Source with Laser Triangulation for Ambient Mass Spectrometry of Nonplanar Samples.

The analysis of nonplanar samples in ambient mass spectrometry poses a formidable challenge. Here, an ion source equipped with laser triangulation for analyzing nonplanar surfaces was constructed. It was designed as a two-position device, where the sample height was measured using laser triangulation and the target compounds were then analyzed. Thanks to a stage movable in xyz, the ion source maintained an optimal vertical distance between the sample and the sampling capillary for each measured spot during the surface analysis. The xyz-coordinates for the movement of the sample stage were computed using the laser sensor data in such a way as to avoid direct contact of the sampling capillary and the measured surface. The ion source performance and its ability to analyze various morphologies were tested using desorption electrospray ionization with plastic objects coated by 2,5-dimethoxybenzoic acid. The experiments showed excellent performance for nonplanar samples but also revealed some limitations especially on object edges and steep slopes. The applicability of the ion source operated in desorption electrospray ionization and desorption atmospheric pressure photoionization was examined for food and pharmaceutical samples. Chemicals on the surface of nonplanar samples were probed along a line extending across the surface of the measured objects. The device provided high-quality spectra, regardless of the sample height at the measured spot. The automatic adjustments of the sample stage in xyz proved to be beneficial for analyzing nonplanar samples and for simultaneous measurement of samples with various dimensions and shapes.