Simultaneous flow injection analysis of paracetamol and ascorbic acid with multiple pulse amperometric detection

The present work reports a simple and quick strategy for simultaneous determination of paracetamol (PC) and ascorbic acid (AA) in pharmaceutical formulations using flow injection method with multiple pulse amperometric detection. The method allows the resolution of the mixture without chemical pretreatment of the sample or electrode modification or the use of chemometric techniques for data analysis. The compounds are detected by applying four sequential pulses (waveform) in function of time to a three-electrode amperometric system that uses a wall-jet cell with gold as working electrode. AA is direct detected at + 0.40 V and PC is indirectly detected at 0.0 V by the reduction (desorption) of the oxidation product (N-acetyl-p-benzoquinoneimine) electrochemically generated at + 0.65 V. The fourth potential pulse (- 0.05 V) is applied for the complete regeneration (cleaning) of the gold electrode surface. The linear response range was optimized between 5 and 24 mg L-1 for AA and 50 and 240 mg L-1 for PC. The difference between the two responses ranges (10-fold) present correlation with the concentration of these compounds in two different pharmaceutical formulations available in the Brazilian market. The analytical frequency was calculated in 60 injections per hour. The use of the proposed methodology for PC quantification in the presence of higher AA concentrations was also carried out. Using the standard addition method, it was possible to detect PC in trace levels (LD = 0.2 mg L-1) in the presence of 880-fold more of AA (176 mg L-1).