High-throughput analysis of arsenic-based pigments in historical book bindings using laser ablation coupled to inductively coupled plasma-mass spectrometry and micro-X-ray fluorescence

A microplate-based high throughput method for the identification of arsenic-containing pigments in historical book bindings was developed. Both laser ablation coupled to inductively coupled plasma-mass spectrometry (LA-ICP-MS) and micro-X-ray fluorescence (μXRF) are capable of rapid high-throughput analyses of large numbers of samples on custom made quartz plates after non-destructive transfer of the analytes using cotton swabs. This is achieved by the precise sequential targeting of sample positions using a moving sample stage. The method is well suited to the direct analysis of solid samples without the need for further sample preparation. This approach was applied to the analysis of As-based pigments in 174 samples from 141 historical books, covering a time period from 1700 to 1952. Wipe sampling based on cotton swabs is employed as a minimally invasive sampling technique to gather loose and potentially harmful pigment particles from different book surfaces. The LA-ICP-MS and μXRF methods were optimized for the rapid detection of As and Cu, allowing for the analysis of 88 samples in 18 min and 147 min, respectively. Dedicated software was developed to automatically process the data and assign samples to one of four pigment groups, further improving the viability of the presented workflow for large sample sizes. A total of 33 samples were found to contain As-based pigments, with 31 samples containing Emerald Green (As and Cu) and 2 samples containing Orpiment (As only). The results are shown to be both consistent for the two methods and reproducible for repeated analyses. The software-based assignment was validated using Raman spectroscopy.