Toward Silica‐Free Compliance: A Low‐Viscosity Sample Pretreatment Methodology for Crystalline Quartz Quantification in Viscous Pastes

Crystalline quartz, the most common crystalline silica polymorph, is widely found in industrial products. It is of high regulatory relevance, because its fine fraction, a form of respirable crystalline silica, is classified as an occupational carcinogen, with product-content thresholds (e.g., 0.1% (w/w) in the European Union) and stringent occupational exposure limits. Since larger size fractions can be reduced to the fine one during work processes and use, a silica-free approach should be pursued, driving the need for accurate and sensitive quantification of crystalline quartz, even in complex matrices. X-ray diffraction (XRD) is a reference technique for selective quartz determination; however, paraffin-rich abrasive and polishing pastes pose a major analytical challenge due to their dense, viscous rheology, which prevents homogeneous incorporation of crystalline internal standards or spikes required by validated quantitative XRD approaches (e.g., EN 13925, EN 17289). Here, we develop and optimize a low-viscosity sample pretreatment, termed low-viscosity doping (LVD), to overcome matrix-driven inhomogeneity. LVD mitigates rheological constraints, enables uniform internal-standard distribution, and improves the reliability of quantitative XRD. Using LVD, crystalline quartz mass fractions were determined with good accuracy and repeatability at levels well below the 0.1% product threshold. The proposed workflow is standardized, time-efficient, and compatible with modern benchtop diffractometers, potentially paving the way for a standard aimed at enhancing safety compliance and risk mitigation in the abrasive and polishing products industry.