Influence of transport tube materials on signal response and drift in laser ablation-inductively coupled plasma-mass spectrometry

Abstract

The influence of commonly applied transport tube materials in LA-ICP-MS on signal intensities and temporal drift was investigated experimentally. Four types of tube materials in different lengths (PVC, nylon, Teflon, copper) were studied. The results demonstrate that PVC and nylon tube materials influence the ionization conditions within the ICP, especially when using longer tubes. The wash-out of hydrogen and oxygen containing components from these were found to enhance signal intensity (up to 70%) and cause a drift in element-to-Ca ratios over time of up to 25%. This drift can take as long as 1.5–2 h and exceeds typical warm up times of ICP-MS instruments. The presence of hydrogen and oxygen changed the plasma most significantly. The results indicate that the tube degassing process (desorption of the gas molecules from the wall of the tubings into the gas stream) has a larger influence on the plasma conditions than the gas or water diffusion through the tubes. This degassing process using PVC and nylon was time and tube length dependent. Previously observed signal enhancements using hydrogen addition to argon were similar to those measured in this study and most significant when using longer tubes (10 m). The effects of these tube materials did not occur when combining laser ablation with solution nebulization. Teflon and copper tubes provided the most stable intensities and element-to-Ca ratios, which remained unchanged within a few % independent of length. Therefore, these tube materials are highly recommended for the acquisition of high precision LA-ICP-MS data.