某些滴眼剂常采用磷酸盐缓冲液配制。磷酸盐缓冲液是由无水磷酸二氢钠和磷酸氢二钠组成,由于磷酸的二级电离常数(K_2=6.23×10~(-8))较大,当以酚酞作指示剂,用氢氧化钠标准液滴定缓冲液中的主药含量时,除主药能与标准液定量作用外,磷酸二氢钠亦能与氢氧化钠标准液发生下列反应:NaH_2PO_1+NaOH=Na_2HPO_1+H_2O所以,其结果并不代表制剂中主药的含量,而是主药和磷酸二氢钠含量的总和。我国近年来出版的制 Some eye drops are often formulated with phosphate buffered saline. Phosphate buffer is composed of anhydrous sodium dihydrogen phosphate and disodium hydrogen phosphate. Because of the large secondary ionization constant of phosphoric acid (K 2 = 6.23 × 10 -8), when using phenolphthalein as indicator, Sodium hydroxide standard titration buffer in the main drug content, in addition to the main drug with the standard quantitative effect, the sodium dihydrogen phosphate can also react with the sodium hydroxide standard reaction: NaH2PO_1 + NaOH = Na_2HPO_1 + H_2O Therefore, The result does not represent the content of the main drug in the preparation, but the sum of the main drug and the sodium dihydrogen phosphate content. China’s publishing system in recent years