3D printed graphite-based electrode coupled with batch injection analysis: An affordable high-throughput strategy for atorvastatin determination

This work integrated a lab-made conductive graphite/polylactic acid (Grp/PLA, 40:60% w/w) filament into a 3D pen to print customized electrodes (cylindrical design). Thermogravimetric analysis validated the incorporation of graphite into the PLA matrix, while Raman spectroscopy and scanning electron microscopy images indicated a graphitic structure with the presence of defects and highly porous, respectively. The electrochemical features of the 3D-printed Gpt/PLA electrode were systematically compared to that achieved using commercial carbon black/polylactic acid (CB/PLA, from Protopasta®) filament. The 3D printed Gpt/PLA electrode "in the native form" provided lower charge transfer resistance (Rct = 880 Ω) and a more kinetically favored reaction (K⁰ = 1.48 × 10^-3 cm s^-1) compared to the 3D printed CB/PLA electrode (chemically/electrochemically treated). Moreover, a method by batch injection analysis with amperometric detection (BIA-AD) was developed to determine atorvastatin (ATR) in pharmaceutical and water samples. Using the 3D printed Gpt/PLA electrode, a wider linear range (1-200 μmol L^-1), sensitivity (3-times higher), and lower detection limit (LOD = 0.13 μmol L^-1) were achieved when compared to the CB/PLA electrode. Repeatability studies (n = 15, RSD <7.3%) attested to the precision of the electrochemical measurements, and recovery percentages between 83 and 108% confirmed the accuracy of the method. Remarkably, this is the first time that ATR has been determined by the BIA-AD system and a low-cost 3D-printed device. This approach is promising to be implemented in research laboratories for quality control of pharmaceuticals and can also be useful for on-site environmental analysis.

A simple, fast, portable and selective system using carbon nanotubes films and a 3D-printed device for monitoring hydroxychloroquine in environmental samples

In this work, an electrochemical method was developed for rapid and sensitive detection of hydroxychloroquine (HCQ), an ineffective candidate drug for COVID-19 treatment however widely consumed during the pandemic, in aqueous samples using a multi-walled carbon nanotubes (MWCNT) film produced through the interfacial method on the indium tin oxide electrode (ITO). According to Raman spectroscopy, X-ray diffraction, UV-vis spectroscopy, Energy-dispersive X-ray spectroscopy, scanning electron microscopy, and atomic force microscopy, the interfacial method produces homogeneous thin films of carbon nanotubes on the substrate surface, which keep connected to the surface forming a three-dimensional microporous structure. The electrochemical behavior and oxidation kinetics of HCQ were also investigated in the MWCNT film. The sensor showed a 7 times higher oxidation current for (69.88 μA) for HCQ than the ITO electrode (9.33 μA) due to the electrocatalytic properties MWCNTs. The ITO-modified electrode was assembled on a portable 3D-printed batch-injection cell for the amperometric detection of HCQ. The oxidation peak current of HCQ is linearly proportional to the concentrations of HCQ ranging from 1.0 to 100.0 μmol L^-1, with a limit of detection of 0.27 μmol L^-1. Water samples (river and tap water) were spiked with HCQ, without the need for dispendious pretreatment (except filtration), and analyzed by the portable system, revealing the detection of HCQ with the recovery of 92.0%-99.8%, which suggested the great potential for real environmental monitoring application.

Lab-made 3D-printed electrochemical sensors for tetracycline determination

Antibiotics such as tetracycline (TC) are widely prescribed to treat humans or dairy animals. Therefore, it is important to establish affordable devices in laboratories with minimal infrastructure. 3D printing has proven to be a powerful and cost-effective tool that revolutionizes many applications in electrochemical sensing. In this work, we employ a conductive filament based on graphite (Gr) and polylactic acid (PLA) (40:60; w/w; synthesized in our lab) to manufacture 3D-printed electrodes. This electrode was used "as printed" and coupled to batch injection analysis with amperometric detection (BIA-AD) for TC sensing. Preliminary studies by cyclic voltammetry and differential pulse voltammetry revealed a mass transport governed by adsorption of the species and consequent fouling of the redox products on the 3D printed surface. Thus, a simple strategy (solution stirring and application of successive potentials, +0.95 V followed by +1.2 V) was associated with the BIA-AD system to solve this effect. The proposed electrode showed analytical performance comparable to costly conventional electrodes with linear response ranging from 0.5 to 50 μmol L^-1 and a detection limit of 0.19 μmol L^-1. Additionally, the developed method was applied to pharmaceutical, tap water, and milk samples, which required minimal sample preparation (simple dilution). Recovery values of 92-117% were obtained for tap water and milk samples, while the content found of TC in the capsule was close to the value reported by the manufacturer. These results indicate the feasibility of the method for routine analysis involving environmental, pharmaceutical, and food samples.

Determination of organophosphorus compounds in water and food samples using a non-enzymatic electrochemical sensor based on silver nanoparticles and carbon nanotubes nanocomposite coupled with batch injection analysis

This work presents, for the first time, a fast and highly sensitive electrochemical method for determination of three organophosphorus compounds (OPs), diazinon (DZN), malathion (MLT), and chlorpyrifos (CLPF), using a modified pyrolytic graphite electrode (PGE) coupled to batch injection analysis system with multiple pulse amperometric detection (BIA-MPA). The PGE was modified by a nanocomposite based on functionalized carbon nanotubes (CNTf) and silver nanoparticles (AgNPs). The OPs samples were directly analyzed on the modified working electrode surface by BIA-MPA system in Britton-Robinson (BR) buffer 0.15 mol L^-1 at pH 6.0. The MPA detection of DZN, MLT and CLPF was performed using two potential pulses, which were sequentially applied on modified PGE at -1.3 V (100 ms) and +0.8 V (100 ms) for selective determination of these three OPs and working electrode cleaning, respectively. Under optimized conditions, the sensor presented a linear range of 0.1-20 μmol L^-1 for DZN, 1.0-30 μmol L^-1 for MLT and from 0.25 to 50 μmol L^-1 for CLPF. The limits of detection (LOD) and quantification (LOQ) of 0.35 and 1.18 μmol L^-1 for DZN, 0.89 and 2.98 μmol L^-1 for MLT, and 0.53 and 1.78 μmol L^-1 for CLPF were obtained. The proposed method exhibited high sensitivity of 0.068, 0.030 and 0.043 mA L μmol^-1 for DZN, MLT and CLPF detection, respectively. Furthermore, the BIA-MPA system provided an analytical frequency of 71 determinations per hour for direct determination of these OPs in water and food samples. The modified PGE coupled to BIA-MPA system showed a high stability of electrochemical response for OPs detection with relative standard deviation (RSD) of 1.60% (n = 20). The addition-recovery studies of the proposed method were carried out in tap water, orange juice, and apple fruit real samples, which showed suitable recovery values between 77 and 124%. The analytical performance of the developed sensor provides an attractive alternative method for OPs determination with great potential for a fast and sensitive application in contaminated samples with these pesticides.

Couple batch-injection analysis and microfluidic paper-based analytical device: A simple and disposable alternative to conventional BIA apparatus

Under controlled dispersion conditions, sample injection towards a detector opened essential fields for the Analytical Chemistry fast development methods. Flow injection analysis (FIA) and batch injection analysis (BIA) systems are crucial for injecting the sample in these analytical methods. The BIA system eliminated the flow manifold, with samples injected directly onto the detector inside the batch injection cell. Paper was slightly evaluated coupled to FIA, and no reports were found associated with BIA. Still, it can potentially reduce the BIA manifold by removing the batch injection cell based on the capillarity properties to disperse the injected solution over the detection system. Hence, this article reported the first work coupling batch-injection analysis and microfluidic paper-based analytical device (BIA-μPAD) with pencil-drawn electrodes directly attached to the paper using a CO₂ laser pre-treated chromatographic paper. The laser pretreatment of the paper (optimized conditions: 6.5% laser power, 12 mm s^-1 scan rate, and 12 mm output distance) was essential to enhance the electrochemical response for ferri/ferrocyanide redox couple and paracetamol (PAR), as shown by spectroscopic and electrochemical techniques. The proposed BIA-μPAD was evaluated using pharmaceutical paracetamol samples as proof-of-concept (optimized conditions: 15 μL injected volume and 6.4 μL s^-1 dispensing rate), obtaining good linearity (R = 0.9961) and recovery values ranging from 95 to 103%. Repeatability (n = 16) and reproducibility (n = 9) tests with 1 mmol L^-1 PAR also presented well relative standard deviation (RSD) results of 5.1% and 6.6%, respectively. A sampling frequency of 76 h^-1 was obtained, which is a similar value compared with conventional BIA apparatus. Limits of detection and quantification were estimated in 0.046 and 0.154 mmol L^-1, respectively. Additionally, an improvement in the current response and the sample throughput was observed when comparing FIA and BIA-μPADs, attesting the applicability of the proposed device and opening for new possibilities related to paper-based devices coupled with flow techniques.

Batch injection analysis with amperometric detection for fluoroquinolone determination in urine, pharmaceutical formulations, and milk samples using a reduced graphene oxide-modified glassy carbon electrode

In this work, the batch injection analysis system with amperometric detection using reduced graphene oxide as a modifier of glassy carbon electrode (GCE) was investigated for the simple, fast, and sensitive monitoring of levofloxacin (LEVO) and ciprofloxacin (CIPRO) in samples of pharmaceutical formulations, synthetic urine, and milk (low- and high-fat content). LEVO and CIPRO were quantified in seven samples using amperometric measurements at +1.10 V vs Ag/AgCl, KCl(sat). The developed methods showed excellent analytical performance with limits of detection of 0.30 and 0.16 μmol L^-1, linear range from 3.0 to 50 μmol L^-1 and 1.0 to 50 μmol L^-1, relative standard deviation below 9.7 and 3.1%, and recovery ranges ranging from 80 to 107% and from 78 to 109% for LEVO and CIPRO, respectively. In addition, the minimum sample preparation (simple dilution) combined with a high analytical frequency (130 to 180 analyses per hour) can be highlighted. Thus, the methods are promising for implementation in routine analysis and quality control to different samples.

A Review on Recent Advances in the Applications of Boron-Doped Diamond Electrochemical Sensors in Food Analysis

The usage of boron-doped diamond (BDD) material has found to be very attractive in modern electroanalytical methods and received massive consideration as perspective electrochemical sensor due to its outstanding (electro)chemical properties. These generally known facilities include large potential window, low background currents, ability to withstand extreme potentials and strong tendency to resist fouling compared to conventional carbon-based electrodes. As evidence of superiority of this material, couple of reviews describing the overview of various applications of BDD electrodes in the field of analytical and material chemistry has been reported in scientific literature during last decade. However, herein proposed review predominantly focuses on the most recent developments (from 2009 to 2020) dealing with the application of BDD as an advanced and environmental-friendly sensor platform in food analysis. The main method characteristics of analysis of various organic food components with different chemical properties, including additives, flavor and aroma components, phenolic compounds, flavonoids and pesticides in food matrices are described in more details. The importance of BDD surface termination, presence of sp² content and boron doping level on electrochemical sensing is discussed. Apart from this, a special attention is paid to the evaluation of main analytical characteristics of the BDD electrochemical sensor in single- and multi-analyte detection mode in food analysis. The recent achievements in the utilizing of BDD electrodes in amperometric detection coupled to flow injection analysis, batch injection analysis, and high-performance liquid chromatography are also commented. Moreover, actual trends in sample preparation techniques prior to electrochemical sensing in food analysis are referred.

Fast quantification of α-lipoic acid in biological samples and dietary supplements using batch injection analysis with amperometric detection

Batch injection analysis (BIA) with amperometric detection, using a pyrolytic graphite electrode modified with cobalt phthalocyanine (PG/CoPc), was employed for determination of α-lipoic acid (ALA) in pharmaceutical product and in synthetic urine samples. The proposed BIA method is based on the application of a potential of +0.9V vs. Ag/AgCl, KCl sat, enabling quantification of ALA over a concentration range from 1.3×10(-6) to 1.0×10(-4)molL(-1), with a detection limit of 1.5×10(-8)molL(-1). A sampling rate of 180 injections per hour was attained and measurements of the reproducibility of successive injections (100µmolL(-1) ALA on the same electrode) showed a RSD of 2.11% for 40 successive injections. The new sensor was utilised for ALA quantification in a dietary pharmaceutical supplement and in synthetic urine and the results obtained for both samples were compared with parallel analysis using high performance liquid chromatography (HPLC), the method recommended by the United States Pharmacopeia. The results obtained were similar (at a 95% confidence level) and in the case of the synthetic urine sample (prepared with a known amount of ALA) the recovery was situated between 98.0% and 102.6%.