碱滴定法测定工业氰基乙酸乙酯的方法通常有3种方法的变化，其一滴定中用指示剂目测滴定终点;其二，用电位法指示滴定终点，滴定中采用自动电位滴定仪;其三，先用水或饱和氯化钠水溶液将试样中的酸萃取入水相中，然后用碱滴定法在水溶液中测定其酸度.对此3种方法的变化作了对比试验，结果表明，在第一种变化中，在所试验的10种指示剂中只有甲基红在终点时有明显的颜色变化，但作为整个方法，测定结果的误差较大;对第二种方法变化，即采用电位滴定法，在终点到达时其滴定曲线中产生明显的突跃，而且按此方法所测得结果精密度和准确度都很好，方法操作方便而快速;对第三种方法变化，经试验用饱和氯化钠溶液作萃取剂的效果较好.经分离后的测定结果与电位滴定法的结果基本吻合，但此方法操作过程长而繁琐.

A comparative study on the results obtained by 3 alternative alkalimetric titration of acidity of ethyl cyanacetate was made and discussed.The 3 alternations are: ① visual detection of end point with indicators;② detection of end-point by potential change,that is,the titration performed by an automatic potentiometric titrator;and ③ acid in the sample was separated by extraction with water or saturated sodium chloride solution and the acidity determined by alkalimetric titration in the aqueous solution.As shown by the experimetal results,for the first alternation,among 10 different indicators tested,methyl red was found to be the best one,giving sharp color change at the end point,but as a whole,results obtained by this method were erroneous.For the second alternation,a clear and sharp inflection was observed potentiometrically at the end-point,and accurate and precise results were obtained by this method.In addition,the automatic potentiometric titration was also rapid and convenient in operation.For the third alternation,by using sat′d NaCl solution as extractant,the results obtained were in consistency with the potentiometric method,but the whole analytical procedure was quite time-consuming and tedious.