关于USP对于滴定液中的基准物质恒重

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列如氢氧化钠滴定液USP 标定要求如下：Accurately weigh about 500 mg of potassium biphthalate, previously crushed lightly and dried at 120° for 2 h, and dissolve in 75 mL of carbon dioxide-free water. Add 2 drops of phenolphthalein TS, and titrate with 0.1 N sodium hydroxide VS to the production of a permanent pink color.
就想问下这里的120℃2小时是指干燥 还是连续2次2小时 干燥至恒重？

欣赏者。

120度干燥2小时即可，无需恒重