A potentiometric, enantioselective membrane electrode for S-ramipril assay

A potentiometric, enantioselective membrane electrode based on graphite paste (graphite powder and paraffin oil), impregnated with 10(-3) mol l(-1) 2-hydroxy-3-trimethyl-ammoniopropyl-beta-cyclodextrin (as chloride salt) solution, is proposed for S-ramipril assay. This sensor can be used reliably for the assay of S-ramipril as raw material (enantiopurity tests), as well as in its pharmaceutical formulations, in the concentration range from 1.80 x 10(-5) to 2.3 x 10(-1) mol l(-1),with a detection limit of 1 x 10-5 mol l(-1), and with an average recovery of 99.94% (RSD = 0.030%) (recovery test), employing the potentiometric technique. The enantioselectivity was determined versus D-proline. It was shown that L-proline is the only main interfering compound. The surface of the electrode can be regenerated by simply polishing it to obtain a fresh surface which is ready to be used in a new assay.