When sourcing HPQ, the most critical factor is the impurity level, typically measured in parts per million (ppm) or parts per billion (ppb). For high-end applications like semiconductors or solar cells, you must ensure the total impurity content is below 20 ppm, with specific focus on Alkali metals (Li, Na, K) and Transition metals (Fe, Ti, Cu). Additionally, verify the particle size distribution (e.g., 50-150 mesh) and hydroxyl (OH) content, as these directly impact the thermal stability and transparency of the final quartz glass.