Amplified anodic electrogenerated chemiluminescence of tris(2,2′-bipyridyl)ruthenium(II) for ultrasensitive detection of bambuterol: Application to content uniformity testing
Introduction
Electrochemiluminescence (ECL) that combines the features of both electrochemistry and photoluminescence is a highly promising technique for the determination of diverse samples in different complicated matrices as plasma and urine with ultra-selectivity and sensitivity [[1], [2], [3]]. Ru(bpy)32+ ECL is widely applicable in many application (biologically and environmentally) rather than other luminophores [4,5]. Ru(bpy)32+ ECL has been utilized pharmaceutically for the detection of different pharmaceutical active ingredients such as antibiotics and antidepressants drugs [[6], [7], [8]]. Specifically, anodic ECL of Ru(bpy)32+ has undergone a huge advancement in many important fields for humans as clinical investigations, environmental analysis, food and drug monitoring [9]. In such systems, ECL intensity could be enhanced by using coreactants for Ru(bpy)32+ [[10], [11], [12]]. Coreactant ECL shows superiority than annihilation ECL in analytical applications due to the single potential sweep, using aqueous buffered solutions (environmentally friendly), and the radical species are generated at lower potentials than organic solvents [13].
Bambuterol hydrochloride (BAM) (Fig. 1) is an important drug that is used as the first line of treatment for asthma. It is an ester prodrug of terbutaline (TER). It has an affinity for lung tissue, a relative stability to pre-systemic metabolism, and a relative specificity for hydrolysis by butyryl-cholinesterase enzyme (liberating TER) [14]. Given once daily, BAM controls the symptoms in asthmatic patients with lower side effects than those produced from TER given twice or three times daily [15]. Antiasthmatic effect of BAM was attributed to its sympathomimetic and B2 agonistic action. Also, BAM has a long acting bronchodilator effect which plays a vital role in the treatment of asthma [16]. Though different analytical methods such as spectroscopic [[17], [18], [19], [20], [21], [22], [23], [24]], chromatographic [[25], [26], [27], [28], [29], [30], [31]] and electrophoretic methods [32] have been reported for the detection of BAM, most of these methods involve complicated analytical procedures, highly expensive instrumentation and analysis, and harmful reagents used in the extraction procedures. Moreover, most of the electrochemical sensors for BAM detection used complicated synthetic procedures for fabrication of different nanomaterials for modification of the surface of the electrodes [33,34]. In contrast, ECL technique is simple and sensitive in a wide dynamic range. In addition, it is considered a green chemistry as most of ECL reports didn't used organic solvents. In this report we have used the features of ECL technique for the determination of BAM in its pure form and its tablets dosage form. BAM could act as a stable and efficient coreactant for Ru(bpy)32+. To our knowledge it is the first ECL report for determination of BAM. The new ECL system exhibits high sensitivity and high specificity for BAM detection in tablet dosage form (Scheme 1). Additionally, the developed ECL method is fast, facile, easily operated and highly sensitive in comparison with reported methods (Table S1). Furthermore, the developed ECL system was used to establish the content uniformity testing of BAM in its tablets.
Section snippets
Chemicals and reagents
BAM powder (98.79%) was kindly provided by multiapex pharma Company, Badr city – Cairo. Bambec tablets were purchased from a pharmacy in Egypt. Ru(bpy)3Cl2·6H2O, luminophore was obtained from Sigma Aldrich. Phosphate buffer solution (PBS) with various pH values was formed by mixing appropriate volumes from Na2HPO4 and Na3PO4 solutions.
Instrumentation
Shanghai CHI Instruments Company, located in China provided us a CHI 660C electrochemistry workstation for recording the cyclic voltammetric measurements using
Electrochemistry and ECL of Ru(bpy)32+/BAM system
Ru(bpy)32+ and BAM solutions were tested by cyclic voltammetry to check their electrochemical behaviors (see Fig. 2A). A reversible characteristic peak for the redox reaction of Ru(bpy)32+/3+ was obtained at about 1.1 V (Au vs Ag/AgCl) in the absence of BAM. Surprisingly, the presence of BAM makes a little enhancement in the current of the oxidation peak of Ru(bpy)32+ and a slight quenching effect on reductive current. These results clearly indicate to the electrocatalytic oxidation of BAM by
Linearity, LOD and LOQ
Fig. 5 exhibits the constructed calibration plot for BAM detection based on Ru(bpy)32+ luminophore. Using amperometric conditions, ECL signal intensity and BAM concentrations was directly proportional to each other with a good linearity (R2 = 0.999) from 10 nM to 2.0 μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 1.48 nM and 5.0 nM, respectively. Based on ICH recommendations [39], validation parameters for example linearity, LOD and LOQ were calculated using
Analysis of tablets and comparison with the reference spectrofluorimetric method
Bambec® tablets containing BAM active ingredient was tested using the new ECL system and the reference method [22] as well. The average percentage recovery for the assay of the tablets was 100.04 ± 1.34 as listed in Table 1. The results obtained from the developed ECL system and those of the reference method were statistically compared using t- and F- tests at 95% confidence interval. The calculated values of t and F are lower than the tabulated values; this indicates there is no significant
Conclusion
In this work, we reported BAM as an efficient stable coreactant for Ru(bpy)3 2+ ECL without the addition of any catalysts for the first time. The developed ECL system permits the detection of Ru(bpy)3 2+ and BAM (in its pure powder form and tablets dosage form) with good sensitivity and reproducibility. Furthermore, the content uniformity testing of BAM in its Bambec® tablets was investigated by the developed ECL method with average percentage recovery of 99.31 ± 0.98%. The new ECL system has
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Nature Science Foundation of China (21574085), the Natural Science Foundation of Guangdong Province (2016A030312002, and 2017A030313067) and Faculty of Pharmacy, Mansoura University, Egypt.
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