Detection of S-enantiomers of cilazapril, pentopril and trandolapril usinga potentiometric, enantioselective membrane electrode

A potentiometric, enantioselective membrane electrode based on graphite pas te (graphite powder and paraffin oil), impregnated with 10(-3) mol/L 2-hydr oxy-3-trimethylammoniopropyl-beta-cyclodextrin (as chloride salt) solution, has been constructed. The potentiometric, enantioselective membrane electr ode can be used reliably for the enantiopurity tests of S-cilazapril (I). S -pentopril (II) and S-trandolapril (III) in the concentration range of 10(- 5)-10(-2) (I), 10(-6)-10(-2) (II), 10(-4) 10(-2) mol/L (III), a detection l imit of 5.0 x 10(-6) (I), 5.0 x 10(-7) (II), 7.58 x 10(-5) mol/L (III) and with an avenge recovery of 99.36% (RSD = 0.27%) (I), 99.79% (RSD = 0.17%) ( II), 99.77% (RSD = 0.22%) (III), using a chronopotentiometric (zero current ) technique. The enantioselectivity was determined versus D-proline. It was shown that L-proline is the main interfering compound. The surface of the electrode can be regenerated by simply polishing it to obtain a fresh surfa ce which is ready to be used in a new assay.