Determination of Benzocaine Using HPLC and FIA with Amperometric Detection on a Carbon Paste Electrode

A new method for benzocaine determination employing FIA and HPLC with electrochemical detection on a carbon paste electrode was developed. The optimum conditions for the determination were found. Carrier solution for FIA consisted of B–R buffer pH 4 (80 % methanol, v/v) and used flow rate was 1.0 mL min^?1. Mobile phase for HPLC consisted of B–R buffer pH 4 (75 % methanol, v/v) with flow rate 0.4 mL min^?1. Working potential of +1.2 V was employed. Practical applicability of the methods was tested on the determination of benzocaine in selected pharmaceuticals. The results were in agreement with results obtained using spectrophotometric detection and with one exception also with the content declared by the manufacturer.     

Screen‐printed Electrode Modified with ZnFe2O4 Nanoparticles for Detection of Acetylcholine

In this paper a sensor to detect acetylcholine on the basis of ZnFe₂O₄ nanoparticles modified screen printed electrode (SPE) is reported. In the range 0.08–500.0 μM, with the detection limit of 0.024±0.001 μM, acquired anodic peak currents where shown to be linearly dependent on acetylcholine concentrations by differential pulse voltammetry (DPV). It was proven that acetylcholine oxidation at adjusted electrode surface takes place at 100 mV potential less positive compared to an unadjusted screen printed electrode. The electron transfer coefficient (α=0.51) and diffusion coefficient (D=9.3×10^?6 cm²/s) of acetylcholine oxidation were determined too. In addition, this original sensor possesses numerous benefits such as reproducibility, high stability and rapid response (20 s).     

Batch‐injection versus Flow‐injection Analysis Using Screen‐printed Electrodes: Determination of Ciprofloxacin in Pharmaceutical Formulations

This article highlights the potential use of multi‐walled carbon‐nanotube modified screen‐printed electrodes (SPEs) for the amperometric sensing of ciprofloxacin and compares the association of batch‐injection analysis (BIA) and flow‐injection analysis (FIA) with amperometric detection. Both analytical systems provided precise (RSD<5 %) and sensitive determination of ciprofloxacin (LOD<0.1 μmol L^?1) within wide linear range (up to 200 μmol L^?1). Accuracy of both methods was attested by recovery values (93–107 %) and comparison with capillary electrophoresis. The BIA system is completely portable (especially due to association with SPEs) and provided faster analyses (130 h^?1) and more sensitive detection than the FIA system due to the higher flow rates of injection.     

Simple and Fast Determination of Warfarin in Pharmaceutical Samples Using Boron‐doped Diamond Electrode in BIA and FIA Systems with Multiple Pulse Amperometric Detection

This paper proposes the use of the boron‐doped diamond electrode (BDDE) in flow and batch injection analysis (FIA and BIA) systems with multiple‐pulse amperometric (MPA) detection for the determination of warfarin (WA) in pharmaceutical formulations. The electrochemical behavior of WA obtained by cyclic voltammetry (CV) in 0.1 mol L⁻¹ phosphate buffer shows an irreversible oxidation process at +1.0 V (vs Ag/AgCl). The MPA was based on the application of two sequential potential pulses as a function of time on BDDE: (1) for WA detection at +1.2 V/100 ms and; (2) for electrode surface cleaning at −0.2 V/200 ms. Both hydrodynamic systems (FIA‐MPA and BIA‐MPA) used for WA determination achieved high precision (with relative standard deviations around 2 %, n =10), wide linear range (2.0−400.0 μmol L⁻¹), low limits of detection (0.5 μmol L⁻¹) and good analytical frequency (94 h⁻¹ for FIA and 130 h⁻¹ for BIA). The WA determination made by the proposed methods was compared to the official spectrophotometric method. The FIA‐MPA and BIA‐MPA methods are simple and fast, being an attractive option for WA routine analysis in pharmaceutical industries.     

Electrochemical Detection of Three Monohydroxylated Polycyclic Aromatic Hydrocarbons Using Electroreduced Graphene Oxide Modified Screen‐printed Electrode

An electrochemical sensor for detection of three monohydroxylated polycyclic aromatic hydrocarbons (OH?PAHs) was fabricated by electrochemical reduction of graphene oxide (E‐rGO) on screen‐printed electrode (SPE). The E‐rGO film presents typical wrinkled structure with porous and cavity‐like nanostructure, providing large surface area, effective π‐electron system and high electrical conductivity. The developed E‐rGO/SPE sensor exhibits outstanding sensing performance for the target OH?PAHs, 2‐hydroxynaphthalene, 3‐hydroxyphenanthrene, and 1‐hydroxypyrene, within a linear range varying from 50–800 nM, 50–1150 nM, and 100–1000 nM, and with a limit of detection (LOD) of 10.1 nM, 15.3 nM, and 20.4 nM (S/N=3), respectively. The electrochemical sensor possesses excellent stability, acceptable reproducibility, and good anti‐interference ability. Additionally, the proposed sensor can be applied to the analysis of OH?PAHs in the urine samples with recoveries of 98.1–105.9 %.     

Flow Injection Amperometric Detection at Enzyme‐Modified Gold Nanoelectrodes

Gold nanotubular electrode ensembles were prepared by using electroless deposition of the metal within the pores of polycarbonate particle track‐etched membranes. Glucose oxidase (Gox), used as a model enzyme, has been immobilized onto preformed self‐assembled monolayers (mercaptoethylamine or mercaptopropionic acid) on electroless gold via cross‐linking with glutaraldehyde or covalent attachment by carbodiimide coupling. Flow‐injection analysis systems in flow‐through or wall‐jet configurations using these Gox‐modified nanoelectrodes are described. The influence of different experimental parameters (i.e., applied potential, flow rate, interferents…?) on the analytical response of the sensor to glucose has been evaluated. Under optimized conditions, very reproducible results (standard deviations <4%, n=38) were obtained, linear calibration was achieved in the 2×10^?4 M to 3×10^?2 M concentration range and the detection limit was 2×10^?4 M. Moreover, no significant interferences from species like ascorbic and uric acids were observed at a potential of +0.9 V.     

Pulsed Amperometric Detection of Histamine at Glassy Carbon Electrodes Modified with Gold Nanoparticles

Gold nanocrystal‐modified glassy carbon electrodes (nAu‐GCE) were prepared and used for the determination of histamine by flow injection and high performance liquid chromatography using pulsed amperometric detection (PAD) as the detection mode. Experimental variables involved in the electrodeposition process of gold from a HAuCl₄ solution were optimized. A catalytic enhancement of the histamine voltammetric response was observed at the nAu‐GCE when compared with that obtained at a conventional Au disk electrode, as a consequence of the microdispersion of gold nanocrystals on the GC substrate. The morphological and electrochemical characteristics of the nAu‐GCE were evaluated by SEM and cyclic voltammetry. PAD using a very simple potential waveform consisting of an anodic potential (+700 mV for 500 ms) and a cathodic potential (?300 mV for 30 ms), was used to avoid the electrode surface fouling when histamine was detected under flowing conditions. Flow injection amperometric responses showed much higher I_p values and signal‐to‐noise ratios at the nAu‐GCE than at a conventional gold disk electrode. A limit of detection of 6×10^?7 mol L^?1 histamine was obtained. HPLC‐PAD at the nAu‐GCE was used for the determination of histamine in the presence of other biogenic amines and indole. Histamine was determined in sardine samples spiked at a 50 μg g^?1 concentration level, with good results. Furthermore, the chromatographic PAD method was also used for monitoring the formation of histamine during the decomposition process of sardine samples.     

Carbon‐nanotube Modified Screen‐printed Electrode for the Simultaneous Determination of Nitrite and Uric Acid in Biological Fluids Using Batch‐injection Amperometric Detection

A portable electroanalytical system applied for rapid and simultaneous determination of uric acid (UA) and nitrite (NIT) in human biological fluids (urine, saliva and blood) is reported. The system is based on batch‐injection analysis with multiple‐pulse amperometric (BIA‐MPA) detection using screen‐printed electrodes (SPEs) modified with multi‐walled carbon nanotubes. Sample dilution in optimized electrolyte (0.1 mol L⁻¹ Britton‐Robinson buffer pH 2) followed by injection of 100 μL on the electrode surface using an electronic micropipette is performed. UA is detected at +0.45 V and both UA+NIT at +0.70 V. Linear calibration plots for UA and NIT were obtained over the range of 1–500 μmol L⁻¹ with detection limits of 0.05 and 0.06 μmol L⁻¹, respectively. For comparison, a differential‐pulse voltammetric (DPV) method was optimized, and linear calibration plots for UA and NIT were obtained over range of 1–30 μmol L⁻¹ and 1–40 μmol L⁻¹ with detection limits of 0.1 and 0.3 μmol L⁻¹, respectively. BIA‐MPA is highly precise (RSD<1.3 %), fast (160 h⁻¹) and free from sample‐matrix interferences as recovery values ranged from 77 to 121 % for spiked samples (short contact time of sample aliquot with SPE). Contrarily, recovery tests conducted using DPV did not provide adequate recovery values (>150 %), probably due to the longer contact time of the SPE with the biological samples during analysis leading to a severe interference of sample matrices.     

高效阴离子交换色谱-铜/铂修饰电极安培法测定大观霉素

采用阴离子交换色谱分离,在CuSO4溶液中加入少量镧系化合物,经电沉积制备La3+-Cu/pt/CME工作电极,建立了直流安培电化学法(DC)直接检测硫酸大观霉素的方法。考察了流动相浓度、测定电位等参数对色谱分离和测定的影响。在固定相为CarboPac PA10阴离子交换柱、流动相为26mmol/L NaOH,流速为0.6mL/min的色谱条件下,检测电位为0.68V时,硫酸大观霉素峰面积与其浓度在0.12～12mg/L(r=0.9991)和12～280mg/L(r=0.9995)两个范围内呈线性。本方法不需要柱前和柱后衍生化,能同时测定硫酸大观霉素中的主要组分和杂质。修饰电极制作方法简单,催化稳定性好,可作为电化学传感器测定硫酸大观霉素中的各组分。     

铜/金修饰电极-阴离子交换色谱-直流安培法测定阿米卡星注射液组分

建立了一种用阴离子交换色谱分离、以自制铜/金修饰电极为工作电极的直流安培电化学法(DC)直接检测硫酸阿米卡星注射液中主要组分及杂质含量的分析方法。考察了流动相浓度、测定电位等参数对色谱分离和测定的影响。在固定相为CarboPacPA10阴离子交换柱、流动相为26 mmol/L NaOH的色谱条件下,检测电位为0.64 V时,阿米卡星在0.0005~0.02 g/L(r=0.9989)和0.02~0.2 g/L(r=0.9991)两个浓度范围内呈线性。与裸Au电极在采用脉冲安培检测模式(PAD)时相比,电化学检测所需要的碱性强度低(pH<13),而且测定灵敏度高,线性范围宽。本方法不需要柱前和柱后衍生化,能同时测定硫酸阿米卡星注射液中的主要组分和杂质组分。修饰电极制作方法简单,催化稳定性好,可望被应用到流动注射、毛细管电泳等其它流动体系中,对硫酸阿米卡星原料药、注射液等实际样品中的各组分进行测定。     

毛细管电泳柱端盘状电极安培检测区带展宽的定量分析

从理论上分析了影响毛细管电泳法端盘状电极安培区检测区带展宽的诸因素，给出了区带展宽的模拟公式，通过实验考察了进样量，分离电压，检测器体体积对区带展宽的影响并验证了模拟公式。     

Amperometric Biosensors for Tyramine Determination Based on Graphene Oxide and Polyvinylferrocene Modified Screen‐printed Electrodes

A comparison of the analytical characteristics of two tyramine biosensors, based on graphene oxide (GRO) and polyvinylferrocene (PVF) modified screen‐printed carbon electrodes (SPCE), is reported. Diamine oxidase (DAOx) or monoamine oxidase (MAOx) was immobilized onto the PVF/GRO modified SPCE to fabricate the biosensors. Surface characteristics and electrochemical behaviour of the modified SPCEs were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and cyclic voltammetry (CV). Electrode surface composition and experimental variables such as pH and working potential were optimized in order to ensure a high performance. Under optimum experimental conditions, both DAOx/PVF/GRO/SPCE and MAOx/PVF/GRO/SPCE biosensors exhibited wide linear dynamic ranges for tyramine from 9.9×10^?7 to 1.2×10^?4 M and from 9.9×10^?7 to 1.1×10^?4 M, respectively. MAOx/PVF/GRO/SPCE biosensor showed higher sensitivity (11.98 μA mM^?1) for tyramine determination than the DAOx/PVF/GRO/SPCE biosensor (7.99 μA mM^?1). The substrate specifity of the biosensors to other biogenic amines namely histamine, putrescine, spermine, spermidine, tryptamine, β‐phenylethylamine and cadaverine was also investigated. The developed biosensors were successfully used for tyramine determination in cheese sample.     

毛细管电泳脉冲安培检测药物制剂中的氨基酸

基于毛细管电泳三脉冲安培检测技术,同时测定了氨基酸注射液中具有电活性的色氨酸和酪氨酸的含量。研究了三脉冲电位及时间、电解液的浓度、酸度、电泳电压及进样时间对电泳分离和检测的影响,得到了最优测定条件。以铂微盘电极为工作电极,Ag/AgCl为参比电极,三脉冲电位为:E1-900mV,t1100ms;E2700mV,t2100ms;E3950mV,t3100ms,在15mmol/L的磷酸盐(pH=11)缓冲溶液中,上述两组分在10min内完全分离。测定色氨酸和酪氨酸的线性范围分别为1×10-3～5×10-7mol/L和1×10-3～8×10-7mol/L,检出限分别为0.25μmol/L和0.17μmol/L(S/N=3);平行进样的峰电流相对标准偏差(RSD)分别为2.9%和3.3%(n=7)。     

Batch‐injection Amperometric Analysis on Screen‐printed Electrodes: Analytical System for High‐throughput Determination of Pharmaceutical Molecules

This work presents a single analytical system able to perform high‐throughput determinations of different pharmaceutical molecules on screen‐printed electrodes (SPEs) assembled on a batch‐injection analysis (BIA) cell. Two types of SPEs, both containing a carbon conductive ink as working electrode, were selected for the determination of levamisole (LVM) in aqueous and sodium levothyroxine (NaLVT) in hydroethanolic media. The main analytical characteristics of the proposed system for both examples are high precision (RSD <3.8 %, n=10), low detection limits (submicromolar range), and high sample‐throughput (>150 h^?1) using a single SPE, demonstrating the extended lifetime of such sensors, which are adequate for routine pharmaceutical analysis. The proposed analytical system requires battery‐powered portable devices, including potentiostat and reader, electronic micropipette, BIA cell and SPEs, and can be applied for a wide range of pharmaceutical molecules. In case of analyte adsorption on electrode surface, fast electrode cleaning can be supplied by external stirring easily adapted to the cell, which is demonstrated in this work for NaLVT determination.     

Determination of Amlodipine and Atenolol by Batch Injection Analysis with Amperometric Detection on Boron‐doped Diamond Electrode

This work describes the sequential determination of amlodipine (AML) and atenolol (ATN) by batch injection analysis (BIA) with pulsed amperometric detection (BIA‐PAD). Boron doped diamond (BDD) was used as working electrode. AML was detected at +1.00 V and ATN at +1.65 V. The proposed BIA method is simple, robust, precise (RSD <3.2 %; n=10), presents high analytical frequency (>70 injections h^?1), generates reduced volume of waste (without use of organic solvent) and requires minimal sample manipulation (dissolution and dilution in electrolyte). The limits of detection were 0.074 and 0.073 µmol L^?1 for AML and ATN, respectively. The results obtained with the proposed BIA method were compared to those obtained by HPLC and similar results were obtained (at 95% of confidence level).     

Direct Electrochemistry of Hemoglobin Immobilized on Carbon‐Coated Iron Nanoparticles for Amperometric Detection of Hydrogen Peroxide

A novel method for preparation of hydrogen peroxide biosensor was presented based on immobilization of hemoglobin (Hb) on carbon‐coated iron nanoparticles (CIN). CIN was firstly dispersed in a chitosan solution and cast onto a glassy carbon electrode to form a CIN/chitosan composite film modified electrode. Hb was then immobilized onto the composite film with the cross‐linking of glutaraldehyde. The immobilized Hb displayed a pair of stable and quasireversible redox peaks and excellent electrocatalytic reduction of hydrogen peroxide (H₂O₂), which leading to an unmediated biosensor for H₂O₂. The electrocatalytic response exhibited a linear dependence on H₂O₂ concentration in a wide range from 3.1 μM to 4.0 mM with a detection limit of 1.2 μM (S/N=3). The designed biosensor exhibited acceptable stability, long‐term life and good reproducibility.     

A Zirconium Oxide Nanoparticle Modified Screen‐printed Electrode for Anodic Stripping Determination of Daclatasvir Dihydrochloride

A novel, sensitive and rapid voltammetric method applied for daclatasvir dihydrochloride (DSV.2HCl) detection in raw material, human plasma and urine using square wave voltammetry at a nano‐screen printed electrode (SPE) based on synthesized zirconium oxide nanoparticles (ZrO₂ NPs). The attention to zirconium oxide nanoparticle syntheses arises from its likely use in making an electrode material in the electroanalytical process. Anodic stripping square wave voltammetric peaks have been recorded at the optimum conditions of drug solution as pH, scan rate, accumulation time and accumulation potential. Morphology of the used nanoparticles has been performed by scanning electron microscope (SEM) and transmission microscope (TEM). ZrO₂ NPs were applied to screen printed electrode (ZrO₂‐MSPE) giving a new sensor to detect the DSV.2HCl drug. ZrO₂ NPs were tested for their electroactivity in improving electrodes sensitivity. The modified electrode has been used for the analysis of DSV.2HCl in spiked serum, spiked urine and pharmaceutical formulation.     

Amperometric Biosensor for Choline Based on Gold Screen‐Printed Electrode Modified with Electrochemically‐Deposited Silica Biocomposite

A mediator‐free choline biosensor was developed using the electrochemically assisted sol‐gel deposition on gold screen‐printed electrodes. The addition of 12 mM of cationic surfactant CTAB in silica sol allowed enhancing the stability of the sensor. The modified electrode demonstrated catalytic activity and stable amperometric response to choline for over 3 weeks of exploitation with the sensitivity of 6 µA mM^?1 and LOD of 6 µM. The interference of ascorbic acid was reduced by pretreating the analyzed solution with MnO₂ powder. The application of the sensor with the purpose of identifying choline in the baby milk demonstrated satisfactory metrological characteristics.     

Incorporation of Disposable Screen‐Printed Electrodes for Use in Capillary Electrophoresis End‐Column Amperometric Detection System

The development and performance of an end‐column amperometric detection system integrated with disposable screen‐printed electrodes for capillary electrophoresis is presented. In this system, the electrode and capillary can be easily replaced and the capillary/electrode alignment procedure is straightforward. The use of easily replaceable screen‐printed electrodes offers a tremendous benefit for capillary electrophoresis applications requiring frequent replacement of the working electrode due to fouling. This simple and convenient system is very attractive for routine analyses by capillary electrophoresis with electrochemical detection. The separation and determination of uric acid in human urine is presented.     

高效液相色谱-脉冲积分安培电化学检测牛奶中的妥布霉素

采用C18键合硅胶柱和脉冲积分安培电化学检测器对妥布霉素样品进行了分离检测。对两种检测电位波形进行了对比，并选取了表现优良的检测电位。方法对妥布霉素的检出限19μg／L，在0．1～25mg／L范围内表现良好线性（r=0．9999）。该方法应用于市售鲜奶的检测，妥布霉素的回收率为98％。