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.     

Electrochemical Portable Method for on site Screening of Scopolamine in Beverage and Urine Samples

Scopolamine (SCP) is a psychoactive drug often added to beverages for recreational or abuse purposes (loss of memory and non‐consensual practices). In this work, a simple and portable method for fast in field screening of SCP in beverage (beer, coke, energy drink, sugarcane spirit, vodka, and whisky) and urine samples is presented. The proposed method is based on batch injection analysis with square wave voltammetric (BIA‐SWV) detection using boron‐doped diamond (BDD) as the working electrode. A voltammetric profile with accurate information on the presence or absence of SCP is obtained using a small sample volume (～50 μL) and a simple sample pretreatment step (dilution in supporting electrolyte). Around two hundred analyses are possible using the proposed system (injection of single sample plug – 120 μL) without the need of electrodes handling or supporting electrolyte exchange (friendly to point‐of‐care or on site screenings). The quantification of SCP in beverages is also possible using the proposed portable protocol, with a limit of detection of 0.18 μmol L^?1 and recovery values between 87 to 113 %.     

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).     

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.     

Thallium Determination at the Single Picomole per Liter Level by Flow‐Injection Differential‐Pulse Anodic Stripping Voltammetry

The flow‐injection differential‐pulse anodic stripping voltammetric (FI‐DP‐ASV) procedure has been developed for the determination of thallium concentration of the order of the single pM. Due to the analyte preconcentration at the electrode, DPASV is among the leaders in competition for achieving a detection limit as low as possible. The enrichment factor can be easily regulated by the duration of the preconcentration time. A DPASV measurement in a flow‐injection system enables the circulation of an analyzed sample and a medium exchange when preconcentration is completed. This approach ensures significant improvement of a background current. The measurements were performed in a cell of the wall‐jet type containing the mercury film electrode. One hour preconcentration was used for the determination of the lowest thallium concentrations. The developed method provides the opportunity to determine thallium in real environmental samples at the single pM level with the detection limit equal to 0.25 pM and RSD equal to 8.2%. This is by more than one order of magnitude better than the lowest detection limit reported in the literature (5 pM). Additionally, the medium exchange resulted in the improvement of the measuring accuracy, which was evidenced by the application of a certified reference material.     

A novel analytical low-cost flow system based on a 0.6 MPa (84 psi) diaphragm pump applied to on-line trace pre-concentration in flame AAS and ICP-OES

A novel inexpensive 0.6 MPa (84 psi) flow system based on a low-cost diaphragm pump has been developed. The unfavourable strong pulsation of the pump has been overcome by using highly flexible silicone tubing as a pulse suppression coil. This results in a smooth pulse-free continuous flow of 100 mL min(-1) in circulation. This flow rate is much too high for a flow-injection system; however, with a restrictor capillary the flow rate required can be tapped off down to a range of 0.1-50 mL min(-1). By employing diaphragm pumps in an analytical flow system the pressure gap between HPLC pumps (2-40 MPa) and peristaltic pumps (<0.2 MPa), mainly used in FIA systems, can be filled. Due to the higher pressure delivered by diaphragm pumps relative to peristaltic pumps, the new flow system can be applied to on-line sample pre-concentration and matrix separation in flame AAS and ICP-OES by using standard HPLC pre-columns or small ion-exchange columns, respectively. In this way, very low detection limits in flame AAS have been reached (Cd 0.07 micro g L(-1), Cu 0.05 micro g L(-1), Co 0.9 micro g L(-1), Ni 0.8 micro g L(-1), Mn 0.7 micro g L(-1), Pb 0.8 micro g L(-1) and Tl 0.2 micro g L(-1)).     

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.     

Batch Injection Analysis with Amperometric Detection for DNA Biosensing Applications

In this work, batch injection analysis with the amperometric detection (BIA‐AD), employing a detection cell designed to adapt a screen‐printed carbon electrode (SPCE) was used for the first time as a robust electroanalytical system for DNA biosensing applications. The sensitive amperometric detection was used to evaluate the structural changes in double‐stranded DNA (dsDNA) after UV‐C irradiation of its solution for a given time. Batching of DNA samples was performed by precise electronic pipette microinjection of an irradiated sample aliquot onto the unmodified activated SPCE surface incorporated in the BIA‐AD system. Using the optimized experimental conditions (40 μL of 1 mg mL^?1 dsDNA in a 0.1 M phosphate buffer of pH 7.4 sampled at the injection speed degree of 6 and detected at the potential of +1.5 V vs silver pseudo‐reference electrode), a time‐dependent response (gradual decrease of amperometric signal up to 58 % after 10 min of the irradiation) was found for the detection of damage to low molecular weight salmon sperm dsDNA. The advantages of this low‐dimensional and cost‐effective measuring system can be utilized not only for the quantification of DNA damage/degradation by UV irradiation, but they are also promising for studying other types of DNA interactions.     

Fast Mapping of Gunshot Residues by Batch Injection Analysis with Anodic Stripping Voltammetry of Lead at the Hanging Mercury Drop Electrode

The forensic analysis of lead in gunshot residues (GSR) sampled on the hands of potential shooters is rendered faster, simpler and less expensive by a new batch injection analysis (BIA) method, based on differential pulse anodic stripping voltammetry (DPASV). A simple “J” shaped adaptor was designed to direct the flux of the analyte injected with a micropipettor onto the hanging mercury drop electrode of any commercial electrode stand. Sampling methods for GSR were compared and lifting with adhesive tape was elected for field use. The tapes are glued on polyethylene screens and stored in capped vials. Sampling with multiple strips provides coarse mapping of the distribution of lead on the shooter's hands. After a dissolution/extraction step with chloroform/aqueous 0.10 mol L^?1 HCl, 100 μL of the aqueous phase are injected during 25 s for accumulation of lead on the HMDE at ?0.60 V (vs. Ag/AgCl). A detection limit of 20 ng/mL of Pb(II), outreaching for GSR analysis, is reached without oxygen removal, at a frequency of 20 injections per hour. Results for sequences of shootings with a revolver and a pistol are presented.     

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.     

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.     

3D‐printed Portable Platform for Mechanized Handling and Injection of Microvolumes Coupled to Electrochemical Detection

We present a low‐cost mechanized system fabricated using fused deposition modelling 3D‐printing technology to manipulate microvolumes and perform injections on an electrochemical cell in wall‐jet configuration. As a proof‐of‐concept, the amperometric detection of paracetamol (model analyte) on a screen‐printed electrode using 0.5 μL aliquots resulted in highly reproducible responses (RSD <3 %). Moreover, handling of microliter aliquots of butylhydroxytoluene (phenolic antioxidant) and 2,2‐diphenyl‐2‐picrylhydrazyl (DPPH) to promote the radical‐scavenging reaction to determine antioxidant capacity by electrochemical detection of residual DPPH was demonstrated (time‐controlled reaction). A final application of the system was devoted to the analysis of cocaine and a common adulterant found in seized samples. The mechanized 3D‐printed analytical platform is capable to execute diverse sample preparation steps on board by handling microliter aliquots and subsequent electrochemical detection. 3D‐printing technology enabled the fabrication of a versatile and low‐cost (<U$200) mechanized system accessible to general chemistry labs.     

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.     

Development of a Novel Versatile Method for Determination of two Antihistamines in Association with Naphazoline Using Cathodically Pretreated Boron‐doped Diamond Electrode

Antihistamines such as pheniramine (PHN) or chlorpheniramine (CPH) are commonly associated with naphazoline (NPZ) in eye drops and nasal decongestants. In this work, a batch‐injection analysis system with multiple pulse amperometric (BIA‐MPA) detection has been applied for the first time for fast simultaneous determination of naphazoline (NPZ) and pheniramine (PHN) or NPZ and chlorpheniramine (CPH). PHN or CPH was selectively detected at +1.1 V and both PHN and NPZ or CPH and NPZ were detected at +1.3 V using boron doped diamond (BDD) as working electrode and Britton‐Robinson (BR) buffer (pH=10.0) as supporting electrolyte. The current of NPZ can then be obtained by subtraction of the currents detected at both potential pulses and applying a correction factor (CF). The proposed method presented good intra‐day repeatability (RSD between 0.7 and 3.2 % for PHN; 0.7 and 2.1 % for CPH; 1.5 and 4.0 % for NPZ; n=20), high analytical frequency (>80 injections h⁻¹), and limits of detection of 0.64, 0.47 and 0.11 μmol L⁻¹ for PHN, CPH and NPZ, respectively. The results obtained with the proposed method are in agreement with those obtained by HPLC (95 % confidence level).     

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).     

Fast and Selective Simultaneous Determination of Acetaminophen,Aspirin and Caffeine in Pharmaceutical Products by Batch Injection Analysis with Multiple Pulse Amperometric Detection

In this work is presented a method for simultaneous determination of paracetamol (PA), acetylsalicylic acid (ASA) and caffeine (CA) in pharmaceutical tablets, using a bare boron‐doped diamond working electrode (BDDE) coupled to batch injection analysis system with multiple pulse amperometric detection (BIA‐MPA). The optimized sequence of fast potential pulses were applied on BDDE for acquisition of independent amperograms: +1.0 V for PA oxidation, +1.3 V for oxidation of PA and salicylic acid (SA) generated from a previous alkaline hydrolysis of ASA and +1.6 V in which the three analytes are oxidized (PA, SA and CA). Selective determination of PA is performed using the currents obtained at +1.0 V, while SA and CA signals are indirectly obtained using simple subtraction operations between peak currents from each amperogram and correction factors (CF's). The limitations of such approach on the precision and accuracy as function of BIA‐MPA conditions are discussed. Simultaneous determination of the target drugs in pharmaceutical tablets was performed by BIA‐MPA and the results compared to a HPLC‐DAD method. Under optimized conditions, the proposed method exhibits fast responses (180 injections per hour for the simultaneous determination of the three analytes) and suitable precision (RSD_PA: 0.78 %; RSD_SA: 1.09 %; RSD_CA: 2.73 %). BIA‐MPA method is simple, portable and presents relative low‐cost.     

Highly Sensitive Voltammetric Speciation and Determination of Inorganic Arsenic in Water and Alloy Samples Using Ammonium 2‐Amino‐1‐Cyclopentene‐1‐Dithiocarboxylate

A simple, fast, reproducible (2.5% RSD at 3.0 μg/L), and sensitive method is described for quantifying As(III) (0.3 μg/L detection limit, 0.5–440 μg/L dynamic range). Anodic stripping voltammetry (ASV) is performed after accumulating arsenic at a mercury film electrode at ?0.350 V vs. Ag/AgCl (saturated KCl) for 20 s in 0.2 M HCl containing 8 μM ammonium 2‐amino‐1‐cyclopentene‐1‐dithiocarboxylate (AACD), without oxygen removal. This is the first report of using AACD in ASV and in electrochemical quantification of As(III). Total arsenic is determined after sodium‐sulfite‐reduction of As(V) to As(III). Interferences are minimal. Method validation involved water and metal alloy samples.     

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.     

Batch Injection Analysis‐Multiple Pulse Amperometric Fingerprint: A Simple Approach for Fast On‐site Screening of Drugs

In this work, the association of batch injection analysis with multiple pulse amperometric detection (BIA‐MPA) is presented as a new approach to obtain drugs fingerprints. To illustrate the potential of this screening method, tablets containing sildenafil as the active substance were used. Here, a sequence of three potential pulses as a function of time (+1.3, +1.6 and +2.1 V) were applied on a boron‐doped diamond electrode while reproducible injections were performed in a BIA cell (wall jet configuration). The chemical profile of the respective drug combined three ratios among the peak currents obtained in each amperogram: R₁=ipa_1.6V/ipa_1.3V, R₂=ipa_2.1V/ipa_1.6V, R₃=ipa_2.1V/ipa_1.3V. This simple protocol allowed discrimination between Viagra® (reference)/generic and two smuggled tablets, as well as pure Viagra® from Viagra® adulterated with other electroactive compounds (caffeine, dipyrone, paracetamol and tadalafil). For comparison, screening of these samples was also performed using square wave voltammetry combined with a chemometric method (principal component analysis), in which was achieved similar discrimination by one or other strategy for the most of drugs. This new BIA‐MPA fingerprinting combines desirable features in forensic science such as low cost, simplicity, high sample throughput (two drugs discerned in less than 30 s) and portability (screening at the place of the seizure).     

Batch Injection Analysis Utilizing Modified Electrodes with Tetraruthenated Porphyrin Films for Acetaminophen Quantification

Batch injection analysis (BIA) utilizing amperometric detection with glassy carbon electrodes modified with [Co(TPyP){Ru(bipy)₂Cl}₄](TFMS)₅?H₂O porphyrin films were explored for acetaminophen analysis in pharmaceutical formulations. BIA is an interesting alternative for application of electrodes modified with tetraruthenated porphyrins. This sensor exhibited sharp current response peaks, rapid washout and excellent reproducibility for BIA‐amperometric quantification of acetaminophen. Also, a wide linear working range (10^?4 to 10^?6 mol L^?1) as well as high sensitivity and sampling frequency rate (detection limit=1.1×10^?7 mol L^?1, sampling frequency=120 injections/h) and a small volume of analysis (100 μL/injection) was achieved. Furthermore, the proposed method permits the direct quantification of acetaminophen in many pharmaceutical products, avoiding cumbersome processes as previous separations, solvent extraction or sample filtration. The new procedure was applied to the analysis of commercial pharmaceutical products and the results were in excellent agreement with the ones obtained by spectrophotometric method. Accordingly, this amperometric method showed to be very well suited for quality control analysis and other applications with similar requirements.