Capabilities of automated LA-ICP-TOFMS imaging of geological samples

Abstract

Element imaging aims to provide quantitative data on multi-element distributions from major to trace elements with high lateral resolution. Here, we describe a control system for laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) imaging with complex integration of translational stage, laser, and mass spectrometer data acquisition which was tested on glass and mineral samples. In particular, besides single pulse imaging at a laser repetition rate of 100 Hz using a 5 μm laser spot size, a hole drilling imaging approach provided higher pixel sensitivity and lower limits of detection (<1 mg kg⁻¹ for most heavy elements) while maintaining the same lateral resolution. An optional surface cleaning pulse can be applied without additional recording of data. Furthermore, the ablation area can be adapted to specific object structures of interest and leads to significant shorter imaging times. Triggering the data acquisition for every ablation position led to binned pixel data in relation to the sample position. This simplifies the data evaluation and allows a more automated image generation. The approach presented in this study enables flexible adjustments of distinct ablation modes to a specific analytical task and provides the basis for fully automated element imaging. To test the applicability of our approach, two complex geological samples containing crystalline solids were imaged to gain insights into the distribution of trace elements that occur typically in the low mg kg⁻¹ range. We show that both single pulse and hole drilling ablation modes allow the determination of a large number of trace elements. However, the hole drilling mode shows a superior sensitivity per pixel, which in turn provides more detailed information about the formation of geological samples.