Flow injection analysis of doxycycline or chlortetracycline in pharmaceutical formulations with pulsed amperometric detection

A flow injection with pulsed amperometric detection for determination of doxycycline or chlortetracycline in pharmaceutical formulations is described. Doxycycline or chlortetracycline were studied at a gold rotating disk electrode with cyclic voltammetry as a function of pH of supporting electrolyte solution. The optimized PAD waveform parameters were obtained with a flow injection system. The optimized pulsed conditions of doxycycline were 1150 mV (versus Ag/AgCl reference electrode) detection potential (E_det) for 220 ms (150 ms delay time and 70 ms integration time), 1500 mV (versus Ag/AgCl reference electrode) oxidation potential (E_oxd) for 70 ms oxidation time (t_oxd) and 250 mV (versus Ag/AgCl reference electrode) reduction potentail (E_red) for 400 ms reactivation time (t_red). The optimized pulsed conditions of chlortetracycline were 1050 mV (versus Ag/AgCl reference electrode) detection potential (E_det) for 300 ms (200 ms delay time and 100 ms integration time), 1300 mV (versus Ag/AgCl reference electrode) oxidation potential (E_oxd) for 70 ms oxidation time (t_oxd) and 250 mV (versus Ag/AgCl reference electrode) reduction potentail (E_red) for 400 ms reactivation time (t_red). The optimized PAD waveform was applied to the determination of doxycycline hydrochloride and chlortetracycline hydrochloride standard solution and in pharmaceutical formulations. The linear dynamic ranges of doxycycline hydrochloride and chlortetracycline hydrochloride were 1 μM–0.1 mM. The sensitivity of this method was found to be 23 μA/mM for doxycycline hydrochloride and 33.76 μA/mM for chlortetracycline hydrochloride. The detection limit for both compounds is 1 μM. The doxycycline hydrochloride and chlortetracycline hydrochloride content in commercially available tablet dosage forms by the proposed method was comparable to those specified by the manufacturer.     

The fabrication and performance of an Ag/AgCl reference electrode in human serum

A simple set of electric circuits was used to assemble a pulse generator. With pulse potentials and under galvanostatical control, a clean silver wire was anodized electrochemically for 0.2–0.5 min in 1.0 mol l⁻¹ HCl with a pulse current density of 20 mA cm⁻², and the pulse wave parameters of t_a/t_c = 1 and a cycle of 4 s forming an Ag/AgCl reference electrode. Even though the AgCl layer was consumed during the working period when the Ag/AgCl electrode was used as a cathode, the AgCl layer could be in situ recovered electrochemically in serum used when a reversed potential was applied to the electrode system immediately after the measuring program was finished. The current response curve of the anode indicated that an AgCl layer in high density was basically accomplished during the first 6 pulse cycles in human serum. In order to keep a stable and uniform AgCl layer on the reference electrode after each measuring cycle, the ratio of the recovery time (t_r) to the working time (t_w) was measured and the smallest value was obtained at 0.03. The open-circuit potential of the Ag/AgCl electrode with respect to a SCE in 0.1 mol l⁻¹ KCl was monitored over a period of 14 days and the mean value was 40.09 mV vs SCE with a standard deviation of 2.55 mV. The potential of the Ag/AgCl reference electrode did remain constant when the measurements were repeated more than 600 times in undiluted human serum with a standard deviation of 1.89 mV. This study indicated that the Ag/AgCl reference electrode could been rapidly fabricated with a pulse potential and could be used as a reference electrode with long-term stable properties in human serum samples.     

银掺杂聚L-酪氨酸修饰电极同时测定多巴胺、肾上腺素和抗坏血酸

用循环伏安法制备银掺杂聚L-酪氨酸修饰玻碳电极,研究了多巴胺、肾上腺素和抗坏血酸在其电极上的电化学行为,建立了同时测定多巴胺、肾上腺素和抗坏血酸的新方法。当3种组分共存时,在磷酸盐缓冲溶液(pH6.0)中,扫描速率为140mV/s,多巴胺和肾上腺素在修饰电极上分别产生还原峰,峰电位分别为0.198和-0.205V,多巴胺和肾上腺素氧化峰重叠,峰电位为0.313V(vs.Ag/AgCl);抗坏血酸产生一个氧化峰,峰电位0.108V(vs.Ag/AgCl)。多巴胺和肾上腺素的ΔEpc=0.403V,抗坏血酸的氧化峰与多巴胺和肾上腺素的ΔEpa=0.205V,用还原峰和氧化峰可同时测定多巴胺、肾上腺素和抗坏血酸,3种组分同时测定的线性范围分别为5.0×10-6～1.0×10-4mol/L,8.0×10-6～1.0×10-4mol/L和3.0×10-5～1.0×10-3mol/L;检出限分别为5.0×10-7,8.0×10-7和5.0×10-6mol/L。本方法用于人尿液中多巴胺、肾上腺素和抗坏血酸的同时测定,结果满意。     

Effect of anode materials on the characteristics of the miniature Clark-type oxygen electrode

A miniature Clark-type oxygen electrode was fabricated using semiconductor techniques. A two-electrode configuration was used and the effect of different anode materials on the characteristics of the oxygen electrode was examined. The cathode and anode were formed in anisotropically etched grooves and calcium alginate gel containing 0.1 M KCl electrolyte filled the grooves. A gas-permeable membrane was directly formed over the gel. By using an Ag/AgCl anode instead of a gold electrode, the response time was shortened, the residual current was decreased and the linearity of the calibration graph was improved. Good linear calibration graphs were obtained by using the Ag/AgCl anode. The Ag/AgCl anode oxygen electrode produced a stable current for 5 h at ?0.8 V and for 22 h at ?0.6 V.     

Electropolymerised o-phenylenediamine film as means of immobilising lactate oxidase for a L-lactate biosensor

The immobilisation of L-lactate oxidase at a platinum electrode was achieved by entrapping the enzyme within an o-phenylenediamine film at 0.65 V (vs. Ag/AgCl). Anodic detection of the product of the enzymatic reaction, i.e., hydrogen peroxide, at 0.75 V (vs. Ag/AgCl) was employed for the quantification of L-lactate using amperometric batch and flow injection methods. This technique allows the enzyme to be entrapped in a strongly adherent thin membrane. The sensor exhibits a very fast response time, an active enzyme loading of 5 mU/cm(2) electrode surface, and high sensitivity with a detection limit of 2.46 x 10(-7)M. A sample throughput of 180/hr, precision of 3.53% for 25 injections and linearity up to 1.5mM were obtained in flow injection analysis studies. The one-step procedure for sensor preparation requires 20 min, and the discriminative properties of the polymer film show great promise as a means of excluding interfering compounds commonly found in serum.     

Studies of the chlorpheniramine solid-state ion-selective electrode

An Ag/AgCl solid-state electrode was prepared by using urea-formaldehyde resin as the frame material and KCl powder as the active material. Using the prepared Ag/AgCl solid-state electrode as substrate and chlorpheniramine tetraphenylborate ion-pair complex as the active component, a new type of solid-state chlorpheniramine ion-selective electrode was constructed. The properties of the electrode were studied in detail. The electrode shows a rather good stability and can be used in the potentiometric determination of chlorpheniramine.     

三种食用色素的电化学行为的理论计算与验证

用量子理论计算柠檬黄、日落黄、胭脂红的相对焓（Hm）、相对熵（Sm）,计算柠檬黄、日落黄、胭脂红的还原电位分别为-0．969,-0．901,-0．854V（vs．Ag／AgCl／Cl）。探讨了琼脂对色素的电催化机理,采用循环伏安法在玻碳琼脂电极上研究了食用色素柠檬黄、日落黄、胭脂红的电化学行为,分别于-1．064,-0．910,-0．882V（vs．Ag／AgCl／Cl）产生还原峰,理论预测与试验结果基本一致。     

无液接裸露式Ag/AgCl参比电极的研制及应用

提出了一种无液接裸露式Ag/AgC l参比电极制备方法,测试了该参比电极的稳定性、重现性、可逆性、响应时间、温度影响等因素。实验结果表明,该电极电位稳定在49 mV,响应时间在30 s以内时,具有重现性、可逆性好,使用寿命长,温度影响小等特点,可替代饱和甘汞和Ag/AgC l参比电极。     

一种全固态扑尔敏电极的研制

制备了以脲醛树脂为框架，以ＫＣｌ粉末为活性组分的Ａｇ／ＡｇＣｌ固体电极。结果表明该电极具有相当好的稳定性并能用于扑尔敏制剂的含量测定。     

Disposable Anodic Stripping Voltammetric Sensor for Heavy Metal Analysis in Environmental Samples

A disposable sensor was developed for anodic stripping voltammetric analysis of heavy metals utilizing the HgO-modified composite electrode technique. It was prepared by integrating a HgO-modified electrode, Ag/AgCl reference electrode and carbon counter electrode on a polycarbonate strip by screen printing technique.     

集成化金膜阵列电极的制作研究

以聚乙烯不干胶掩膜版法结合金属溅射沉积技术在FR-4玻璃纤维版上制作了由6个金膜工作电极(1 mm×2 mm)、1个大面积金膜对电极(2 mm×13 mm)和1个厚膜Ag/AgCl参比电极构成的集成化金膜阵列电极系统,并利用电化学手段对阵列电极系统进行了考察。研究结果表明,K3Fe(CN)6在厚膜Ag/AgCl/1.0 mol/L NaCl参比电极上的式电位与商业Ag/AgCl/3.0 mol/L NaCl参比电极相差0.067 V;参比电极放置1个月后,测量电位未发生明显变化。利用扫描电化学显微镜对工作电极表面平整度进行考察,结果表明工作电极表面具有较好的平整度。通过测量H2SO4还原峰面积评价了工作电极电化学面积的批内、批间一致性;通过K3Fe(CN)6在电极上的Ipa/Ipc比值评价了工作电极电化学特性的批内、批间一致性。结果表明,阵列电极面积和电化学特性具有良好的批内和批间一致性。对集成化金膜阵列电极系统的研究结果表明,聚乙烯不干胶掩膜版法结合金属溅射沉积技术制作的阵列电极能够满足电化学电极的要求,可作为电化学生物传感器的基础电极。     

Electroanalysis of tetracycline using nickel-implanted boron-doped diamond thin film electrode applied to flow injection system.

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 microM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.     

Use of a copper electrode in alkaline medium as an amperometric sensor for sulphite in a flow-through configuration

A flow injection analysis (FIA) method has been developed for the determination of sulphite in beverages. The method is based on the amperometric detection (0.60 V vs Ag/AgCl (sat. NaCl)) of the analyte at a copper surface in an alkaline medium (1 M NaOH solution) with a manifold that incorporates flow extraction of sulphite as SO2 through a PTFE membrane. Under optimal experimental conditions the peak current response increases linearly with sulphite concentration over the range from 1.0 to 5.0 mM. The repeatability of the electrode response in the FIA configuration was evaluated as 4% ( n =20), the limit of detection of the method was 0.04 mM (S/N =3) and the analytical frequency was 50 h(-1). Since ethanol is also electroactive and permeates through the PTFE membrane, a strategy involving in a first step measurements of only ethanol by manipulating the pH of the donor stream was employed for wine samples. Then, both ethanol and sulphite were measured at the copper electrode at 0.40 V vs Ag/AgCl (sat. NaCl) and the sulphite concentration was determined by difference. Results for 3 different beverage samples (alcoholic and non-alcoholic) showed excellent agreement with the ones obtained by using a recommended procedure for sulphite analysis.     

A wall-jet disc electrode for simultaneous and continuous on-line measurement of sodium dithionite, sulfite and indigo concentrations by means of multistep chronoamperometry

In this paper, a multistep chronoamperometric method is presented to measure continuously and simultaneously the concentrations of indigo, sodium dithionite and sulfite for application in textile dyeing processes. The method is based on the oxidation of sodium dithionite and the reduced form of indigo at a platinum disc electrode. Sodium dithionite is oxidized at a potential of 0.3 V versus Ag/AgCl and shows transport controlled steady state currents at a rotating disc electrode and a wall-jet electrode. The latter has been developed for the purpose of the application. Implementation of a wall-jet instead of a rotating disc electrode is much easier and cost-effective. Indigo is oxidized at −0.55 V versus Ag/AgCl to a virtually water insoluble product, which precipitates at the electrode surface. Indigo behaves quasi-reversibly, and is reduced at a potential of −0.9 V versus Ag/AgCl. In order to clean the electrode surface this reduction is used as a step in the multistep sequence. Finally, sulfite is oxidized at a potential of 0.8 V versus Ag/AgCl but did not give rise to well defined transport controlled limiting currents. However, determination of its concentration is still possible within error margins of 5%.     

Control of Interfacial Potentials and Redox Reactions on Bipolar Electrodes Using Ag/AgCl

The interfacial potential difference on the surface of bipolar electrodes was controlled by placing Ag/AgCl on part of the electrode. Oxygen reduction on the cathodic pole was coupled with an electrochemiluminescence (ECL) reaction on the anodic pole. In an open bipolar system, the ECL intensity depended on the location of Ag/AgCl and the concentration of Cl⁻ ions. A current flowed through Ag/AgCl and the ratio of currents generated at the anodic and cathodic poles was affected by the position of Ag/AgCl. Further, the effect of Ag/AgCl placement was also demonstrated in a closed bipolar system using hydrogen peroxide (H₂O₂) and glucose as analytes. Ag/AgCl was also effective in adjusting the sensitivity to these analytes to achieve the best performance. This method of interfacial potential control is expected to contribute toward the development of reliable sensing devices and applications such as redox cycling, which require precise potential control.     

Voltammetric characterization of a fully integrated, patterned single walled carbon nanotube three-electrode system on a glass substrate

A single walled carbon nanotube (SWCNT)-based three-electrode system was fully integrated on glass substrates using a standard microfabrication process and electrochemically characterized using cyclic voltammetry. O(2) plasma functionalization of the SWCNT film working electrode for achieving high sensitivity was voltammetrically optimized with respect to the plasma power and treatment time. Chlorination of a Ag thin-film was done in an acidic solution for different dip times to form a thin-film Ag/AgCl reference electrode. The Nernstian behavior of as-prepared and seven-day-aged Ag/AgCl thin-film electrodes was investigated for seeking the optimum reference electrode with long-term stability and was compared to a commercial reference electrode. A quality control evaluation and a performance assessment of the fully integrated SWCNT-transferred sensing systems were performed using cyclic voltammetry. The proposed SWCNT-based three electrode device exhibited clear electrochemistry under voltammetric conditions, and is therefore a candidate for use in all electrochemical biosensors.     

Determination of ascorbyl 6-palmitate in food matrices by amperometric flow injection analysis

In this paper a rapid method based on a FIA (flow injection analysis) system with amperometric detection for the evaluation of ascorbyl 6-palmitate in foods is described. The selectivity of the proposed method is related to the low anodic potential applied to the working glassy carbon electrode (+0.1 V vs. Ag/AgCl) that leaves out interferences from ascorbic acid and phenolic compounds. By flow injection analysis, under optimised conditions, the calibration curve was linear in the range 0-20 mg l(-1) and the detection limit was 0.2 mg l(-1).     

Amperometric Determination of Lactic Acid. Applications on Milk Samples

Abstract

A hydrogen peroxide electrochemical sensor, coupled with immobilized lactate oxidase and covered with a cellulose acetate dialysis membrane has been applied in flow analysis of lactate in milk samples. The hydrogen peroxide produced by the enzymatic reaction is measured with a platinum electrode polarized at +650 mV versus Ag/AgCl. Milk samples were analyzed and compared with a spectophotometric reference method. The developed procedure is very simple and the short response time allows its use in assaying milk samples on dairy farms.     

An Arrayed Micro‐glutamate Sensor Probe Integrated with On‐probe Ag/AgCl Reference and Counter Electrodes

Complete all‐in‐one multi‐arrayed glutamate (Glut) sensors have been constructed on a silicon‐based micromachined probe composed of micro‐platinum (Pt) working electrodes, a micro‐silver/silver chloride (Ag/AgCl) reference electrode (RE), and a micro‐Pt counter electrode (CE). The OCP shift of the electrodeposited Ag/AgCl on‐probe micro‐reference electrode compared with a Ag/AgCl wire is <0.1 mV/h. The composition ratio of Ag, Cl, and Pt on the electrodeposited on‐probe micro‐reference electrode is observed to be 1.00 : 0.48 : 0.02 analyzed by EDS. The miniaturized amperometric Glut biosensors were constructed on working electrode sites (electrode area: ∼8.5×10⁻⁵ cm²) of the microprobe modified with glutamate oxidase (GlutOx) enzyme layers for the selective, fast, and continuous detection of L‐glutamate. The sensor selectivity towards common electroactive interferents has been improved significantly by coating the electrode surface with perm‐selective polymer layers, overoxidized polypyrrole (PPY) and Nafion®. The sensitivity, detection range, and response time of the proposed all‐in‐one Glut biosensors are 204.7±5.8 nA μM⁻¹ cm⁻² (N=5), 4.99–109 μM, and 2.7±0.3 sec, respectively and no interferent signals of AA and DA were observed. The sensor can be reused over 19 times of continuous repetitive operation (total measurement time: ∼4 hours) and the sensor sensitivity can retain up to four weeks of storage.     

Study of an Au colloid self-assembled electrode and its application to the determination of carbon monoxide

A novel electrochemical sensor has been developed for the detection of carbon monoxide. The chemically modified electrode, prepared by reaction of cysteine and then an Au colloid of size approximately 15 nm with a platinum microelectrode, has excellent catalytic activity toward carbon monoxide, with an oxidation potential of +600 mV relative to the Ag/AgCl electrode. The CO gas sensor is based on an Au colloid self-assembled modified electrode as working electrode, an Ag/AgCl electrode as reference electrode, a Pt electrode as counter electrode, and a porous film which is in direct contact with the gas-containing atmosphere. The effects on the determination of CO of different internal electrolyte solutions of perchloric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphate buffer of different concentrations were also studied. The sensor is characterized by a short response time and highly reproducible detection of CO. This sensor can be used in the field of environmental monitoring and control.