为确定HPLC 法测定霉酚酸有关物质所用流动相的合理pH 值，配制pH 值为4.5 和5.5的流动相，采用Kromasil C18色谱柱（4.6 mm×200 mm，5 μm×100A）对霉酚酸进行有关物质的测定，对于同一个样品连续进样6 次，按照面积归一化法进行计算，以霉酚酸百分含量的相对标准偏差（RSD%）来确定流动相的合理pH 值。结果显示采用pH 值为4.5 的流动相进行霉酚酸有关物质的HPLC 测定，其测定结果稳定性好、灵敏度高、重现性好，可用于霉酚酸有关物质的测定。

Mycophenolic acid related substance was analyzed by HPLC equipped with Kromasil C18 chromatogram column (4.6 mm×200 mm, 5 μm×100A) and the reasonable pH of mobile phase was determined. The same sample was analyzed for 6 times and determined according to area normalization method. The optimal pH of mobile phrase was determined on the basis of relative standard deviation (RSD%) of mycophenolic acid percentage. The method showed good stability, high sensitivity and good reproducibility when the pH value of the mobile phrase was 4.5.