Purification method of melphalan impurity D

The invention discloses a method for purifying a melphalan impurity D. The method comprises the following steps: preparing a mobile phase A, a mobile phase B, a diluent and a sample solution; the sample liquid is purified by using preparative high performance liquid chromatography, and the conditions are as follows: the flow rate is 10 mL/min to 40 mL/min; the column temperature is 10 DEG C to 30 DEG C; the sample size is 1-5 ml; the detection wavelength is 200 nm to 220 nm; a chromatographic column is octadecyl silane bonded silica gel; gradient elution is carried out by adjusting the proportion of organic phases in gradient elution; the method comprises the following steps: taking a sample solution, injecting the sample solution into a preparative high performance liquid chromatograph, and then calculating the peak area percentage of each chromatographic peak in a sample chromatogram according to an area normalization method. The content of an organic phase in gradient elution has a great influence on purif