A sensitive determination method for mexiletine derivatized with dansyl chloride in rat plasma utilizing a HPLC peroxyoxalate chemiluminescence detection system

A sensitive determination method for a non‐fluorescent anti‐arrhythmic drug, mexiletine, in rat plasma is presented utilizing a HPLC peroxyoxalate chemiluminescence (PO‐CL) detection system. After an internal standard (4‐methylmexiletine, 4.35 pmol) and 0.1 N sodium hydroxide solution were added to 5 μL rat plasma, the solution was poured onto an Extrelut 1 column. Both mexiletine and the internal standard were eluted with diethy ether and then the eluate was evaporated to dryness. The residue was dissolved in 0.2 M borate buffer (pH 8.5) and mixed with dansyl chloride (75 nmol) in acetronitrile. After standing of 90 min at room temperature, 0.5 N HCI was added to the reaction mixture to stop the reaction and a 2/45 aliquot of the mixture was subjected to a HPLC PO‐CL detection system using bis(4‐nitro‐2(3,6,9‐trioxadecyloxycarbonyl)phenyl)oxalate (TDPO) and hydrogen peroxide. The calibration curve for mexiletine in rat plasma was linear over the range 20–100 ng/mL plasma (20.6–103 fmol/injection). The detection limit (S/N = 2) was 1.0 fmol over the whole procedure. The method was applied to the measurement of the time courses of plasma mexiletine concentration after oral administration of the drug [25 mg (115.9 μmol)/kg] to rats.