复方苯甲酸搽剂是由苯甲酸和水杨酸等组成的。苯甲酸的Pka=4．18，水杨酸的一级Pka=3．0[1]，两者之差小于4，这样用NaOH标准液滴定时，只能测得两种酸的总含量。文献[2]指出在这种情况下，可以用线性滴定法来测定混合酸的各组分含量。本文根据线性液定法的原理，建立了线性滴? Compound benzoic acid liniment is composed of benzoic acid and salicylic acid and so on. Pka = 4.18 for benzoic acid, and Pka = 3.0 for primary salicylic acid [1]. The difference between them is less than 4, so the total content of the two acids can only be measured with NaOH standard titration. Reference [2] pointed out that in this case, you can use linear titration to determine the mixed acid content of each component. In this paper, according to the principle of linear liquid constant method,