Figure 4: Illustration of the selectivity of the method: (a) banknote extract free of the analyte of interest; (b) banknote extract blank with cocaine standard added at concentration of 4 mg L−1; (c) extract of a banknote in circulation. Legend for the peaks: 1: propranolol (I.S.), 2: cocaine. Experimental conditions: capillary 48.5 cm (length to the detector 40 cm); BGE composed of 20 mmol L−1 HIBA and 60 mmol L−1 TRIS at pH 8.4; injection using 50 mbar for 10 s; voltage 25 kV.