購買的標(biāo)樣還需要分析校正嗎?

購買的標(biāo)樣，證書提供的含量應(yīng)該可以直接用。但如ASTM D5599，“before preparing the standards,determine the purity of the oxygenate stocks and make corrections for the impurities found. Whenever possible,use stocks of at least 99.9% purity. Correct for the purity of the components for water content determined by Test method D1744."

為什么？如何矯正？