外观appearance white crystalline powder 水溶性solubility clear to slightly hazy colorless solution at 10g plus 30ml of water (with warming) 水分water by karl fischer ≤2% 紫外吸收UV absorbance ≤0.1 at 290 nm (25% w/w) 重金属heavy metals ≤5 ppm (as lead) purity by NaOH titration ≥99%