Original articleSimple and cost-effective determination of ciprofloxacin hydrochloride by electrical micro-titration
Graphical abstract
By employing an electrical micro-titration system, in which a capacitively coupled contactless conductivity detector is used to monitor the reaction process in real time, ciprofloxacin hydrochloride in tablet samples is determined. Because the reaction solutions are isolated from the working electrodes, it shows significant simplicity and cost-effectiveness, by eliminating the requirements for detector exchange/renewal between measurements, and by involving no auxiliary chemicals.
Introduction
Titrimetry is popular in both chemical laboratories and the control of various industrial processes [1] because of its intrinsic natures-simplicity, speed and cost-effectiveness [2]. Analytical chemists have extensively employed it for the measurement of major, minor and even trace constituents in complex matrices. Generally, optical- and electrochemical-methods are used to identify the equivalence point. The former is based on color change at the end point [3], [4], and has some distinct advantages (particularly when optical instrumentations are employed), such as satisfactory accuracy and sensitivity and risk-free contamination of head stage. While, optical methods face some challenges: 1) in most case sophisticated optical components and special indicators are required [5], [6]; 2) indicators are rarely completely selective [3]; 3) the need for transparent solutions and vessels is quite strict. The latter is based on the change of electrochemical parameters, such as voltage [7], [8] and current [1], [9] at the working electrodes. In contrast to optics-based devices, photo-electric conversion is not needed for electrochemical devices [10], allowing them to be more easily miniaturized and affordable [11]. However, electrode deterioration is unavoidable [1] and results in erratic measurements that decrease the accuracy because that the tips of the working electrodes must be immersed in the titration solution rather than a noninvasive test [9].
Ciprofloxacin is an antibacterial agent of the fluoroquinolones, and is considered as a broad-spectrum antibiotic used in the treatment of urinary and respiratory tract infections as well as in gastrointestinal and sexually transmitted diseases [12]. High performance liquid chromatography (HPLC) is the official method for determining ciprofloxacin in many countries [12], [13], [14], [15], [16]. However, apart from the requirement of expensive instrumentation, this technique for routine analysis are often time consuming. Recently, numerous methods based on optical [16], [17], [18], [19], [20] and electrochemical [12], [13], [16], [21], [22], [23], [24] techniques have been reported. Among them, those approaches by titration exhibited outstanding performance, and have been used successfully [12], [24]. However, these methods based on either optical techniques or electrochemical techniques, still are candidates longing for further development due to their flaw mentioned above.
Capacitively coupled contactless conductivity detection (C4D) is an attractive alternative of conductivity-based method. Generally, an AC voltage is applied to an actuator electrode, and an AC voltage is capacitively coupled into the electrolyte and measured at the pick-up electrode [25], [26]. The magnitude of the detected signal is proportional to the concentration and mobility of the ionic charge carriers within the solution [27]. Like other electrochemical techniques, C4D offers instrumental simplicity, low cost, rapid response, no transparent solution requirement and easy miniaturization [26], [27], [28]; in addition, it also has an outstanding advantage in comparison with contact electrochemical methods, i.e. a free-risk of contamination because the electrodes are separated from the solution measured. Nowadays many efforts have been made to not only improve the performance of devices [26], [29], [30], but also widen the field of applications [26], [27], [28], [31]. Previously we have used C4D successfully to monitor the process of DNA amplification in real time [32].
We were prompted by the need to develop a simple and cost-effective method for the determination of some commonly used drugs, such as ciprofloxacin hydrochloride (CIPHCl). In this paper, for the first time the C4D was introduced to develop a micro-titration system. And the determination of CIPHCl in tablet was performed further. Though the theoretical basis and applications have been described in many works, the determination of CIPHCl via mictro-titration based on the C4D in this work was worthy of special consideration, as it had a series of significant advantages in comparison with that described in previous literatures.
Section snippets
Characterization of the micro-titration system
The property of the monitoring system, i.e. the C4D, was characterized using a series of AgNO3 solutions at different concentration as probes. It can be seen that the apparent conductivity increases as a function of concentration over the range of 0.5–100.0 mmol/L (Fig. 1). As expected, the curve shows a slight nonlinearity because the presence of a very small capacitive coupling between the two electrodes [33]. While, over the same range the contact conductivity also increases as a function of
Conclusion
Based on the developed C4D, a new electrical micro-titration system and a new relevant analytical method (two modes) were constructed. The practicability of this method for the determination of CIPHCl in tablet sample was evaluated successfully. In comparison with some existing analysis methods, including titrations and HPLC, the new approach has some distinct features, and exhibits a unique nature.
- (1)
By employing the C4D to real time monitor the titration, there is totally risk-free for the head
Reagents and chemicals
CIPHCl standard (C17H18ClFN3O3, CAS: 86393-32-0) was kindly supplied by National Standard Material Research Center (Beijing, China). The tablet sample of CIPHCl was purchased from a local pharmacy and was freshly prepared just before the analysis. Silver nitrate was purchased from Aladdin Chemical Reagent Co., Ltd. (Shanghai, China). Ammonium ferric sulfate dodecyl hydrate and other chemicals were all purchased from Shanghai Chemical Reagent Co. (Shanghai, China) and were all of analytical
Acknowledgments
The authors gratefully acknowledge the financial support from Key R&D of Shandong Province (No. 2016GSF120008) and Qingdao National Laboratory for Marine Science and Technology (No. 2015ASKJ02-05).
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