IN CLINICAL STUDIES, THERE IS AN INCREASING DEMAND FOR AN EFFICIENT ANALYTICAL METHOD THAT PERMITS SIMULTANEOUS SEPARATION AND QUANTIFICATION OF DRUGS IN A COMPLEX MATRIX WITH LESS LABORATORY WORK [1]. ASSAYS NEED TO BE FREE OF INTERFERENCES, NOT ONLY FROM ENDOGENOUS SUBSTANCES AND OTHER CONCOMITANTLY ADMINISTERED DRUGS, BUT ALSO MUST DISTINGUISH BETWEEN PARENT DRUG AND ITS METABOLITES [2]. ANTIARRHYTHMICS ARE USED TO TREAT DISORDERS OF THE HEART'S RHYTHM. MOST OF THE CURRENTLY AVAILABLE ANTIARRHYTHMICS HAVE A NARROW THERAPEUTIC INDEX, NECESSITATING CAREFUL DOSE ADJUSTEMENT [3]. IN THIS STUDY, A NEW METHOD WAS DESCRIBED FOR THE ENRICHMENT OF ANTIARRHYTHMIC DRUGS (PROPRANOLOL, METOPROLOL, DILTIAZEM, AND VERAPAMIL) IN PLASMA SAMPLES VIA A DISPERSIVE LIQUID–LIQUID MICROEXTRACTION (DLLME) COMBINED WITH ON-COLUMN STACKING IN CAPILLARY ELECTROPHORESIS. TWO STEPS WERE EMPLOYED FOR BIOLOGICAL SAMPLES CLEAN-UP AND SENSITIVITY ENHANCEMENT IN CAPILLARY ELECTROPHORESIS. THE FACTORS AFFECTING THE ON-LINE SAMPLE STACKING AND MICROEXTRACTION PROCEDURE WERE OPTIMIZED. THIS ASSAY ENHANCED SENSITIVITY157-314FOLD FOR THE STUDIED DRUGS. THE BASELINE SEPARATION WAS ACHIEVED WITHIN 18 MIN. DURING METHOD VALIDATION, THE CALIBRATION CURVES WERE LINEAR OVER A RANGE OF 20-800 NG/ML (R2³0.997). THE RELATIVE STANDARD DEVIATIONS (RSDS) AND RELATIVE ERRORS (RES) OF INTRA- AND INTER-DAY ASSAYS WERE BELOW 20%, WHICH SHOWED GOOD PRECISION AND ACCURACY. THEIR DETECTION LIMITS RANGED BETWEEN 2.5 TO 4.7 NG/ML (S/N=3). THE VALIDATED METHOD IS SUCCESSFULLY APPLIED TO DETERMINE PROPRANOLOL, METOPROLOL, DILTIAZEM, AND VERAPAMIL IN HUMAN PLASMA SAMPLES OBTAINED FROM THE PATIENTS WHOSE RECEIVED THESE DRUGS.