Liquid‐liquid Extraction Coupled to Batch Injection Analysis for Electroanalysis of Levofloxacin at Low Concentration Level

This work presents the integration between phase‐separation by magnetic‐stirring salt‐induced high‐temperature liquid‐liquid extraction (PS‐MSSI‐HT‐LLE) and batch injection analysis with amperometric detection (BIA‐AD) as an alternative strategy for pre‐concentration of analytes before hydrodynamic electroanalysis. To demonstrate the performance of this analytical system, the emerging contaminant levofloxacin was quantified in tap, aquarium and lake water at low concentration level. In the optimized conditions, BIA‐AD enabled fast (160 h⁻¹) and reproducible results (RSD<2 %) and the PS‐MSSI‐HT‐LLE allowed the detection of levofloxacin concentration levels not detected by direct electroanalysis (70 and 80 nmol L⁻¹) corresponding to 100‐folds enrichment factors. The performance of proposed method was evaluated by addition‐recovery test and was obtained satisfactory recovery values (between 70 and 96 %). Moreover, PS‐MSSI‐HT‐LLE allows the pre‐concentration of many samples simultaneously, which is advantageous over pre‐concentration on working electrode surface (stripping methods).     

Electrochemical biosensing for dsDNA damage induced by PbSe quantum dots under UV irradiation

<正>An electrochemical sensor for the detection of the natural double-stranded DNA(dsDNA) damage induced by PbSe quantum dots(QDs) under UV irradiation was developed.The biosensing membranes were prepared by successively assembling 3- mercaptopropionic acid,polycationic poly(diallyldimethyl ammonium) and dsDNA on the surface of the gold electrode.Damage of dsDNA was fulfilled by immersing the sensing membrane electrode in PbSe QDs suspension and illuminating it with an UV lamp. Cyclic voltammetry was utilized to detect dsDNA damage with Co(phen)_3~(3+) as the electroactive probe.The UV irradiation,Pb~(2+) ions liberated from the PbSe QDs under the UV irradiation and the reactive oxygen species(ROS) generated in the presence of the PbSe QDs also under the UV irradiation were the three factors of inducing the dsDNA damage.The synergistic effect of the three factors might dramatically enhance the damage of dsDNA.This electrochemical sensor provided a simple method for detecting DNA damage,and may be used for investigating the DNA damage induced by other QDs.     

Solenoid Micro‐pumps: A New Tool for Sample Introduction in Batch Injection Analysis Systems with Electrochemical Detection

This work presents the use of solenoid micro‐pumps as a new strategy for sample introduction in batch‐injection analysis (BIA). The volume of solution dispensed on each pulse of the solenoid micro‐pump (μL) is used as fixed and reproducible injection volume for BIA. In this system, the injection steps are possible in stopped flow mode resulting in low background noise levels, which would not be possible under continuous flow conditions and using solenoid micro‐pumps. As a proof‐of‐concept, amperometric and square‐wave voltammetric (SWV) determination of dopamine was demonstrated as well as anodic‐stripping voltammetry (ASV) of metals. The micro‐pump provided injections of 14 μL of solution per pulse at 512 μL s⁻¹ over the electrode during electrochemical measurement. Moreover, fast injections of analyte or electrolyte were programmed during deposition or conditioning steps of ASV for analyte preconcentration or electrode cleaning. The proposed system improved limits of detection and sensitivity (2‐fold), precision and sample throughput in comparison with traditional BIA due to enhanced mass transfer and consequent reduced dispersion of analyte, and possible control of injections without analyst intervention. This work opens new possibilities of applications of the BIA system, including on‐line sample treatment (derivatization or dilution steps).     

Electrochemical Properties of Ag@iron Oxide Nanocomposite for Application as Nitrate Sensor

Ag@iron oxide nanocomposite powders were synthesized via a two‐step chemical method. Characterization by UV‐Vis, XRD, SEM‐EDX and TEM revealed they are composed of nanosized crystalline silver particles in strict contact with amorphous iron oxide(s). The electrochemical behavior of the synthesized Ag@iron oxide composite was investigated by cyclic voltammetry. Compared with the single phase‐modified electrodes, the Ag@iron oxide/SPCE electrode exhibits an enhanced cathodic current in response to the target analyte, due to a synergistic effect between Ag crystallites and amorphous iron oxide nanoparticles. An amperometric sensor for detection of nitrate based on Ag@iron oxide modified screen‐printed electrode (Ag@iron oxide/SPCE) has been fabricated, showing a good sensitivity (663 µA mM^?1 cm^?2) and a detection limit of 30 µM.     

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.     

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.     

Electrochemical Oxidation of Astaxanthin on Glassy‐carbon Electrode and its Amperometric Determination Using Batch Injection Analysis (BIA)

This work presents the electrochemical oxidation of the antioxidant astaxanthin on a glassy‐carbon electrode (GCE) and its amperometric determination in salmon samples using a batch‐injection analysis (BIA) system. The proposed BIA method consisted of 80‐µL a fast microliter injection of sample at 193 µL s^?1 on the GCE immersed in the electrolyte, a mixture of acetone, dichloromethane, and water (80 : 10 : 10 v/v), containing 0.1 mol L^?1 HClO₄. Advantages include high precision (RSD of 2.4 %), sample throughput of 240 h^?1, and low detection limit (0.3 µmol L^?1 that corresponds to 0.1 µg g^?1) for the analysis of acetone extracts of salmon samples. Recovery values between 83 and 97 % attested the accuracy of the method.     

Determination of Benzocaine and Tricaine in Fish Fillets Using BIA with Amperometric Detection

A system based on batch injection analysis (BIA) associated with amperometric detection at screen‐printed carbon electrode was used for the precise and rapid quantification of the anesthetics compounds benzocaine and tricaine in fresh fish fillets. Along this study, the best conditions for the BIA‐amperometry system were stablished for the rapid determination of these compounds. The results obtained demonstrate that the proposed method is an interesting alternative to the chromatographic methods, once it allows to perform rapid analysis (more than 300 injections per hour) with low limits of detection (3.02×10⁻⁸ mol L⁻¹ for benzocaine and 3.19×10⁻⁸ mol L⁻¹ for tricaine), using just 80 μL of sample for each analysis. Furthermore, it was possible to obtain high repeatability for both compounds analyzed, demonstrating good performance. The simple sample preparation developed in this study drastically reduced the amount of fat in the fish extract, favoring precision, as shown by the results of the recovery studies of both anesthetics contained in the fish samples (values above 99 % for both analytes).     

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).     

Electrochemical Study of the Interaction of the Alkylating Agent Busulfan with Double Strand DNA

Damage of salmon sperm double strand ss dsDNA in solution or immobilized on screen‐printed carbon electrode (SPCE) induced by incubation of DNA with the antineoplastic alkylating agent busulfan (BUS) at various conditions was detected for the first time by simple electrochemical methods. Chemical changes in DNA bases can be detected through the altered electroactivity of the DNA. Electrochemical voltammetric sensing of damage caused by BUS to dsDNA in solution was monitored by the appearance of peaks diagnostic of the oxidation of guanine and adenine. Moreover, crystal violet, which interacts with the DNA immobilized on SPCEs, was used as an effective electroactive indicator, in combination with cyclic voltammetry and differential pulse voltammetry techniques to monitor the cross‐links or damage to DNA. The interaction between BUS and DNA were determined by the changes in the voltammetric peak of crystal violet. The effects of various conditions upon the crystal violet signal were investigated.     

Development of a Simple and Fast Electrochemical Method for Screening and Stoichiometric Determination of Dimenhydrinate

Dimenhydrinate (DIM) is a salt composed by the combination of two active pharmaceutical ingredients: diphenhydramine (DIP) and 8‐chlorotheophylline (CTP). In this work, the use of batch injection analysis with multiple pulse amperometric detection (BIA‐MPA) was proposed for the first time for fast stoichiometric determination of DIM. DIP (cation) and CTP (anion) were determined simultaneously in pharmaceutical samples with a simple and fast injection procedure (70 injections h^?1). Additional strategies were also proposed for rapid screening of samples containing the DIM salt. By a simple injection of a sample into the BIA system (without using of calibration curve), reliable information about stoichiometry of the DIM salt (1 : 1; DIP:CTP) and presence or absence of interfering species (electroactive) can be achieved.     

Voltammetric Determination of Pb,Cu and Hg in Biodiesel Using Gold Screen‐printed Electrode: Comparison of Batch‐injection Analysis with Conventional Electrochemical Systems

This article compares the use of batch‐injection analysis (BIA) with a conventional batch system for the anodic stripping voltammetric (ASV) determination of Pb, Cu and Hg in biodiesel using screen‐printed gold electrode (SPGE). The optimized BIA conditions were 200 µL of injection volume of the digested samples at 5 µL s^?1 directly on the working electrode of the SPGE immersed in 0.1 mol L^?1 HCl solution. Therefore, BIA‐ASV presented the advantages of low sample consumption, which extended the SPGE lifetime to a whole working day of analyses, and potential for on‐site analysis using battery‐powered micropipettes and potentiostats. Although presenting lower sensitivity than conventional systems, the BIA‐ASV presented detection limit values of 1.0, 0.5 and 0.7 µg L^?1, respectively for Pb, Cu and Hg, a linear range between 20 and 280 µg L^?1, and adequate recovery values (90–110 %) for spiked biodiesel 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.     

Exploring Multiwalled Carbon Nanotubes for Naproxen Detection

The electrochemical oxidation of naproxen was investigated at a multiwalled carbon nanotube (MWCNT)‐modified electrode. A decrease (200 mV) in the overpotential of the naproxen oxidation reaction and considerable (4‐fold) current increase (compared to the bare glassy‐carbon electrode) was observed. Two one‐electron transfers were verified at both bare and MWCNT‐modified electrodes and thus a new mechanism for the electrochemical oxidation of naproxen is proposed. Indicative of a mass transport regime that includes a thin‐layer diffusional process (entrapment of naproxen species within the MWCNT film) is presented as a possible explanation for the lowered oxidation potential and substantial current increase. The anti‐fouling properties of MWCNTs on the amperometric detection of naproxen using a batch‐injection analysis (BIA) system is demonstrated.     

Fast Determination of Ciprofloxacin by Batch Injection Analysis with Amperometric Detection and Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

We report fast, precise, selective, and sensitive electroanalytical methods for the determination of ciprofloxacin in milk and pharmaceutical samples by batch‐injection analysis with amperometric detection (BIA‐AMP) and by capillary electrophoresis with capacitively‐coupled contactless conductivity detection (CE‐C⁴D). Both methods required simple sample preparation protocols before analysis (milk samples were just diluted and tablets powdered and dissolved in electrolyte/water). The analytical features of BIA‐AMP and CE‐C⁴D methods include, respectively, low relative standard deviation values for repetitive measurements (2.8 % and 1.7 %, n=10), low detection limits (0.3 and 5.0 µmol L^?1), elevated analytical frequency (80 and 120 h^?1) and satisfactory accuracy (based on comparative determinations by HPLC and recovery values for spiked samples).     

Electrochemical Study of Interaction Between Clozapine and DNA and Its Analytical Application

Abstract

The interaction between clozapine (CLZ) as an orally administrated antipsychotic drug with double stranded calf thymus DNA (dsDNA) was investigated at electrode surface using differential pulse voltammetry (DPV). Activated carbon paste electrode (CPE) was modified with dsDNA and used for monitoring the changes of the characteristics peak of CLZ in 0.05 M acetate buffer (pH 4.3). The adsorptive stripping voltammetry on dsDNA‐modified carbon paste electrode (dsDNA‐CPE) was used for determination of very low concentration of CLZ. Under optimal conditions, the oxidation peak current is proportional to CLZ concentration in the range of 7×10^?9?1.2×10^?6 mol l^?1 with a detection limit of 1.5×10^?9 mol l^?1 for 180 s accumulation time by DPV. The proposed dsDNA‐CPE was successfully used for determination of CLZ in human serum samples with recovery of 97.0±2.5%.     

Electrochemical Oxidation and Sensitive Determination of Pyrogallol at Preanodized Screen‐Printed Carbon Electrodes

In this study, we report a simple, low‐cost and rapid electrochemical sensor based on the anodically pretreated screen‐printed carbon electrodes (SPCE*) for the determination of pyrogallol in pH 7.0 buffer solutions. Cyclic voltammetric studies show that SPCE* lowers overpotentials and improve electrochemical behaviour of pyrogallol, compared to untreated SPCE. All experimental parameters were optimized to improve voltammetric responses; excellent analytical features were achieved by flow‐injection amperometric methods. A linear calibration plot was obtained for 10‐1000 μM pyrogallol with a slope of 0.0562 μA/μM. The detection limit (S/N = 3) was 0.33 μM. Interferences from some inorganic salts and organic compounds were studied. The assay was applied to the determination of pyrogallol in tap water and lake water, respectively.     

Electrochemical study and flow injection analysis of paracetamol in pharmaceutical formulations based on screen-printed electrodes and carbon nanotubes

Acetaminophenol or paracetamol is one of the most commonly used analgesics in pharmaceutical formulations. Acetaminophen is electroactive and voltammetric mechanistic studies for the electrode processes of the acetaminophenol/N-acetyl-p-quinoneimine redox system are presented. Carbon nanotubes modified screen-printed electrodes with enhanced electron transfer properties are used for the study of the electrochemical-chemical oxidation mechanism of paracetamol at pH 2.0.Quantitative analysis of paracetamol by using its oxidation process (in a Britton-Robinson buffer solution pH 10.0) at +0.20 V (vs. an Ag pseudoreference electrode) on an untreated screen-printed carbon electrode (SPCE) was carried out. Thus, a cyclic voltammetric based reproducible determination of acetaminophen (R.S.D., 2.2%) in the range 2.5 × 10⁻⁶ M to 1 × 10⁻³ M, was obtained. However, when SPCEs are used as amperometric detectors coupled to a flow injection analysis (FIA) system, the detection limit achieved for paracetamol was 1 × 10⁻⁷ M, one order of magnitude lower than that obtained by voltammetric analysis. The repeatability of the amperometric detection with the same SPCE is 2% for 15 successive injections of 10⁻⁵ M acetaminophen and do not present any memory effect.Finally, the applicability of using screen-printed carbon electrodes for the electrochemical detection of paracetamol (i.e. for quality control analysis) was demonstrated by using two commercial pharmaceutical products.     

Fast and Simple Electrochemical Analysis Kit for Quality Control of Narrow Therapeutic Index Drugs

The use of multiple‐pulse amperometry (MPA) for the determination of narrow therapeutic index (NTI) drugs using batch injection analysis (BIA) with carbon screen‐printed electrodes (SPE) is proposed, seeking to develop a practical and low‐cost analysis kit for application in routine quality control of these drugs. The electrochemical behaviors of aminophylline, carbamazepine, clindamycin, colchicine, minoxidil, prazosin, procainamide, theophylline, warfarin and verapamil were evaluated in different electrolytes, but just one, the 0.1 mol L⁻¹ phosphate buffer, pH 7.0, was chosen for determination of all the analytes. The amperometric detection was optimized as a function of the best oxidation potential for carbon SPE for each analyte, which was in a range from 0.7 to 1.1 V. The injection conditions were determined as a function of the velocity and the volume injected by the BIA system, which were 92.5 μL s⁻¹ and 100 μL, respectively. Under these conditions, a good repeatability (RSD<3 %), high analytical frequency (>215 determinations per hour), large linear ranges and low LOD (<0.42 μmol L⁻¹) for all the NTI drugs were obtained. Furthermore, the proposed method provided an easy qualitative analysis of the investigated analytes using MPA detection. The addition‐recovery studies in pharmaceutical samples containing NTI drugs and the comparison with official methods showed that the proposed analysis Kit is a very fast, simple and efficient alternative for quantification of these analytes.     

A Competitor-switched Electrochemical Sensor for Detection of DNA

A competitor‐switched electrochemical sensor based on a generic displacement strategy was designed for DNA detection. In this strategy, an unmodified single‐stranded DNA (cDNA) completely complementary to the target DNA served as the molecular recognition element, while a hairpin DNA (hDNA) labeled with a ferrocene (Fc) and a thiol group at its terminals served as both the competitor element and the probe. This electrochemical sensor was fabricated by self‐assembling a dsDNA onto a gold electrode surface. The dsDNA was pre‐formed through the hybridization of Fc‐labeled hDNA and cDNA with their part complementary sequences. Initially, the labeled ferrocene in the dsDNA was far from surface of the electrode, the electrochemical sensor exhibited a "switch‐off" mode due to unfavorable electron transfer of Fc label. However, in the presence of target DNA, cDNA was released from hDNA by target DNA, the hairpin‐open hDNA restored its original hairpin structure and the ferrocene approached onto the electrode surface, thus the electrochemical sensor exhibited a "switch‐on" mode accompanying with a change in the current response. The experimental results showed that as low as 4.4×10⁻¹⁰ mol/L target DNA could be distinguishingly detected, and this method had obvious advantages such as facile operation, low cost and reagentless procedure.