Standard addition strategies for arsenic quantification in historical books using portable X-ray fluorescence

Quantitative X-ray fluorescence (XRF) analysis of heterogeneous solid materials presents challenges due to matrix effects, surface irregularities, and the absence of suitable reference materials. When it is necessary to preserve the physical integrity of samples, these factors can limit the direct use of conventional destructive techniques such as inductively coupled plasma mass spectrometry (ICP-MS). Portable XRF (p-XRF) becomes the preferred alternative for in situ elemental analysis, although its quantitative performance is often limited. To address these issues, two adapted standard addition strategies were developed to improve the accuracy and reliability of p-XRF determinations of arsenic in cultural heritage materials.

The first approach, the surface extraction calibration method (SECM), quantifies arsenic via swab sampling combined with ICP-MS. The second, the impregnated-support standard addition method (Is-SAM), employs external calibration substrates that allow entirely non-destructive quantification. Both methods were evaluated for arsenic (As) quantification in historical book materials, using inductively coupled plasma mass and optical emission spectrometry (ICP-MS/OES) as reference techniques. Comparative evaluation demonstrated that the impregnated-support SAM approach achieved the highest accuracy, with relative errors between -9 % and +7 % and uncertainties of 4-17 %, meeting the analytical bias criteria reported. The SECM also showed improved performance compared to the fundamental parameters (FP) approach but exhibited larger variability at high As concentrations.

The proposed SAM-based strategies offer significant methodological advances for non-destructive XRF quantification in complex, matrix-dependent samples. The impregnated-support SAM (Is-SAM) in particular achieves higher accuracy and lower uncertainties than conventional approaches, enabling reliable, fully non-destructive elemental analysis. These approaches expand the applicability of portable XRF beyond qualitative screening, enabling accurate elemental quantification in fields where sample integrity is critical.