HPLC determination of related substances in lorazepam and its tablets

Objective:To determine four related substances simultaneously in lorazepam and its tablets by HPLC. Methods:The separation was performed on a C_(18)column (250mm×4.6mm,5μm),the mobile phase was com- posed of 0.05mol·L~(-1)ammonium dihydrogen orthophosphate methanol-acetonitrile (35:35:30,adjust the solu- tion with 1mol·L~(-1)phosphoric acid to a pH of 3.5),the flow rate was 1.0mL min~(-1)and detection at 240nm. Results:The separations of lorazepam and its impurities was good.For impurity B,the calibration curve was linear in the range of 0.1964～19.64μg·mL~(-1)with correlation coefficient 0.9999 and the regression equation being Y= 51.47317X-3.34831,and the detection limit was 3ng;The recovery of assay was 100.1%,and the RSD was 0.4% (n=4).For impurity C,the calibration curve was linear in the range of 0.202-20.2μg·mL~(-1)with corre- lation coefficient 0.9999 and the regression equation being Y=36.32533X-4.37263,and the detection limit was 0.4 ng;The recovery of assay was 101.4%,and the RSD was 1.7% (n =4).For impurity D,the calibration curve was linear in the range of 0.1992-19.92μg·mL~(-1)with correlation coefficient 0.9994 and the regression equation being Y=70.36881X-2.9103,and the detection limit was 0.58 ng;The recovery of assay was 100.8%,and the RSD was 0.5% (n =4).For impurity E,the calibration curve was linear in the range of 0.188-18.8μg·mL~(-1) with correlation coefficient 0.9997 and the regression equation being Y=54.74563X-1.93471,and the detection limit was 0.73 ng ;The recovery of assay was 103.1% ,and the RSD was 0.7% (n =4).Conclusion:The method is simple,sensitive and it is suitable for the determation of the related substances of lorazepam tablets.