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以2，3，6-三甲基-β-环糊精作手性流动相添加剂，C18柱为固定相，考察了流动相的pH和手性流动相添加剂浓度对乳酸对映体分离度的影响，建立了DL-乳酸的拆分定量分析方法。用归一化法分析DL-乳酸时引入了定量校正因子，确定了外标法测定L-乳酸的回归方程、精密度和回收率。测定了米根霉L-乳酸发酵液中D-型异构体的质量分数及其随放置时间的变化情况。

A procedure for the resolution of DL-lactic acid and th edeterminatio n of D-isomer ratio in L-lactic acid fermentation broth by Rhizopus oryzae is desc ribed. The effects of pH of mobile phase and concentration of chiral mobile pha s e additives on resolution of DL-lactic acid were investigated. The optical is om ers of lactic acid were resolved by RP-HPLC with 2,3,6-tri-O-β-cyc lode xtrin(TM-β-CD) as a chiral mobile phase additive, and C18 column as stationary phase, and detected at wavelength 210 nm. The results sh owed that a correction factor should be introduced into the equation for ca lc ulation of the percentage of D-lactic acid, because the UV absorption of D-lac tic acid and L-lactic acid might not be the same when TM-β-CD was presen t. Quantitation was achieved with external standard method, the average rec overy was 100.4%, and the relative standard deviation was 0.82%. This method can be used for the determination of the percentage of D-isomer in L-lactic a cid fermentation broth by Rhizopus oryzae, and it is simple, rapid and accur ate. T he results showed that the mass fraction of D-isomer in the fermented broth inc reased during the period of storage.