Determinação estequiométrica de dimenidrinato e simultânea de 8-cloroteofilina, difenidramina e piridoxina usando análise por injeção em batelada com detecção amperométrica de múltiplos pulsos

Abstract

In this work, the potentiality of batch injection analysis with multiple pulse amperometric (BIA-MPA) detection using boron doped diamond (BDD) electrode was investigated for simultaneous determination of 8-chlorotheophylline (CTF) and diphenhydramine (DIP), and these simultaneously with pyridoxine (RIP) or caffeine (CAF) in pharmaceutical formulations. The simultaneous determination of (CTF) and (DIF) was performed with the application of three sequential pulses in function of time to the BDD electrode using NaAc/HAc 0.05 mol L-1(pH = 4.7) as supporting electrolyte. At 1.35 V/50 ms, CTF was detected (oxidation) without interference of DIF. At 1.80 V/50 ms, both compounds (CTF + DIF) were oxidized. The current of DIF can then be obtained by subtraction of the currents detected during application of both potential pulses using a correction factor. The potential pulse of 0.7 V/200 ms was applied to avoid contamination/passivation of the BDD electrode surface. The proposed method presented stability (RSD = 2.4 e 2.5% for CTF e DIF, respectively; n=20), high analytical frequency (70 injections h-1), linear concentration range between and LOD and DOQ of 2.2 and 7.3 μmol L-1 for CTF and 0.5 e 1.7 μmol L-1 for DIF, respectively. The proposed method was used for simultaneous determination of CTF and DIF in pharmaceutical formulations and the obtained results were similar to those obtained by HPLC (confidence interval = 95%). The same system (BIA-MPA) has also been adapted for simultaneous determination of PIR, CTF e DIF. In this method, the following potential pulses were applied sequentially to the BDD working electrode using H2SO4 0.1 mol L-1 as supporting electrolyte: (a) + 1.25 V/50 ms: oxidation of CTF without interference of the other compounds; b) + 1.60 V/50 ms: oxidation of CTF e PIR without interference of DIF; c) + 1.80 V/50 ms: oxidation of CTF, PIR and, DIF; d) + 1.0 V (150 ms): applied to avoid contamination/passivation of the BDD electrode surface. Simple mathematical expressions and correction factors were used to access the oxidation current of each analyte. The proposed method presented the following results: stability (RSD= 0.9, 1.5 e 1.5% for CTF, PIR and DIF, respectively; n=20), high analytical frequency (~60 injections h-1), linear concentration range between and 20.0 and 60.0 μmol L-1 for CTF and DIF and between 10.0 and 30.0 μmol L-1 for PIR and the LD and LQ of 0.19 and 0.62 μmol L-1 for CTF, 0.54 and 1.81 μmol L-1 for PIR and 0.18 e 0.60 μmol L-1 for DIF. The proposed method was applied for simultaneous determination of CTF, PIR and DIF in pharmaceutical samples and the obtained results were similar to those obtained by HPLC (confidence interval = 95%). A third method (similar to the second) was proposed for simultaneous determination of CAF, CTF e DIF. The applied potential pulses were + 1.10 V (CTF oxidation), +1.40 V (oxidation of CTF and CAF) and, + 1.70 V (oxidation of CTF, CAF and, DIF) using NaAc/HAc 0.05 mol L-1(pH = 4.7) as supporting electrolyte. The proposed BIA-MPA system presented high analytical frequency (120 injections h-1), precision (RSDs < 1.0%, n = 20) and low LD and LQ values (0.31 e 1.03 μmol L-1 for CTF, 0.49 and 1.63 μmol L-1 for CAF and 0.76 and 4.09 μmol L-1 for DIF, respectively. The proposed method was applied for determination of CTF, CAF and, DIF in pharmaceutical sample and the obtained results were similar to those obtained by HPLC (confidence interval = 95%).