本文根据固定PH法测定极弱酸碱原理，直接用NaOH溶液滴定盐酸麻黄碱注射液中盐酸麻黄碱至某一固定pH值．通过NaOH溶液消耗体积与盐酸麻黄碱含量成正比关系，用单标准法求得盐酸麻黄碱的含量．本法在滴定过程中不需确定化学计量点，不需标定滴定剂准确浓度，具有简单、快速、试剂消耗少、结果准确等优点． In this paper, according to the determination of very PH method with a fixed pH method, direct titration of ephedrine hydrochloride ephedrine hydrochloride solution to a fixed pH value with NaOH solution. The consumption volume of NaOH solution is directly proportional to the content of ephedrine hydrochloride, and the content of ephedrine hydrochloride is obtained by single standard method. This method does not need to determine the stoichiometric point in the titration process, and does not need to calibrate the exact concentration of the titrant. The method has the advantages of simple, rapid, less reagent consumption and accurate result.