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通常酸碱指示剂有三点不足:1)变色范围宽,2)临近终点时呈中间色,3)终点不尽满足等当点要求。前两个缺点降低分析的精密度,后者降低准确度。遮蔽指示剂(Screened indicator)在于利用补色染料使终点呈灰色或无色,大大改善了终点敏锐性。目前已有几十种不同组成的遮蔽指示剂,但它们仍只限于个别的pH变色点。遮蔽指示剂消除了通常指示剂的第二缺点,而第三缺点除少数外,反而更加突出。这
Usually acid-base indicator has three deficiencies: 1) a wide range of discoloration, 2) intermediate color near the end, 3) the end point to meet the waiting point requirements. The first two drawbacks reduce the precision of the analysis, which reduces the accuracy. Screened indicator is the use of complementary dyes to make the end gray or colorless, greatly improving the endpoint sharpness. There are dozens of shading indicators of different compositions, but they are still limited to individual pH change points. The shadowing indicator eliminates the second drawback of the usual indicator, and the third drawback, with a few exceptions, is even more pronounced. This