Preconcentration Time Research Articles

Electrified liquid – liquid interface strategy for sensing lactic acid in buttermilk extract

Lactic acid (LA) serves as a freshness marker in certain foods. In the present work, electrified interfaces of different nature (i.e., liquid-liquid and liquid-organogel) have been developed for the quantification of LA. Electrochemical sensing of LA at the liquid-organogel interface revealed that adsorptive stripping voltammetry, with a preconcentration time of 500 s offered better sensitivity. Electroanalytical ability of LA under optimized conditions displayed a detection limit of 0.97 μM and 0.71 μM with sensitivity of 2.84 nA μM−1 and 3.59 nA μM−1 for liquid-liquid and liquid-organogel interfaces respectively. Quantification of LA using the developed methodology has been demonstrated in buttermilk as the real matrix. Analysis demonstrate that electrified liquid-liquid and liquid-organogel interfaces are promising approach for sensing LA in buttermilk extract.

Intercalated graphitic carbon nitride-modified electrochemical sensor for improved quercetin detection in clinical applications

Novel voltammetric methodologies have been developed to facilitate the trace-level analysis of quercetin (QRT) using a graphitic nitride (g-C3N4) intercalated carbon sensor. The integration of g-C3N4 into the sensor matrix has enhanced its structural and surface properties, thereby increasing its sensitivity towards QRT detection. The catalytic behavior of g-C3N4 significantly influences the peak response observed for QRT. Systematic investigations were conducted to explore the influence of various parameters, such as scan rate, pH, pre-concentration time, modifier quantity, and analyte concentration, on the peak current response of QRT. Cyclic voltammetry was employed to evaluate the impact of the scan rate, which facilitated the determination of physicochemical parameters, including the heterogeneous rate constant (kₒ) and the number of electrons (n) involved in the electrochemical reaction. Additionally, the concentration effect of QRT was scrutinized using the Square Wave Voltammetry (SWV) technique, which exhibited superior detection sensitivity with a detection limit of 1.18 nM compared to existing methodologies. Furthermore, the g-C3N4/CPE was employed in real-time analysis of QRT in spiked urine samples and pharmaceutical tablet samples, showing satisfactory recovery results. The electrode also demonstrated good stability over multiple measurements, indicating that g-C3N4/CPE is a promising sensor for QRT detection.

Innovative Use of Carbon Nanotubes in Electrochemical Sensors for the Analysis of Europium in Samples from the Environment

An adsorptive stripping voltammetric method for the determination of trace europium(III) based on the adsorption of europium(III)−cupferron complex on the multiwall carbon nanotubes/spherical glassy carbon (MWCNTs/SGC) electrode modified with a lead film is presented. The method was optimized with respect to the main electrochemical parameters that affect the voltammetric determination (supporting electrolyte, pH, cupferron concentration, deposition potential and time). The calibration graph is linear from 5 × 10−9 to 5 × 10−7 mol l−1 with a correlation coefficient of 0.9993 for europium for a preconcentration time of 80 s. The detection limit for a preconcentration time of 80 s is as low as 1.3 × 10−9 mol l−1 for europium. To confirm the effectiveness of the developed procedure on the MWCNTs/SGC electrode, tests were also carried out on a glassy carbon electrode to compare the detection limits obtained. The developed procedure was tested for the effect of extraneous substances on the europium signal. The proposed method was successfully applied by studying natural samples and certified reference materials.

Investigation of Operational Parameters for Nanoelectrokinetic Purification and Preconcentration.

This work reports on experimental investigations into the operational parameters of nanoelectrokinetic purification and preconcentration, especially utilizing on ion concentration polarization (ICP). ICP as a nanoscale electrokinetic phenomenon has demonstrated promising advances in various fields utilizing an ion depletion zone (IDZ) with a steep electric field gradient inside the ICP layer. However, the inevitable electrokinetic instability occurring within the IDZ has posed a challenge in operating the ICP system stably. To address the need for a stable and efficient ICP operation in various devices and applications, we propose an operational strategy along with conducted research to determine optimal operating ranges. In order to investigate the operational parameters, a unit voltage (VTH) is introduced as the threshold for initiating ICP. We examined the applicability of VTH across various operating ranges to ensure its effectiveness and versatility. In ICP purification, we categorize three modes (steady, burst, and unsteady) based on IDZ expansion and stability under varying VTH and flow rate conditions, presenting optimal operational conditions that minimize the voltage margin. In ICP preconcentration, a systematic investigation is conducted to observe the influence of background electrolyte concentration and voltage conditions on preconcentration efficiency, offering insights into the correlation between preconcentration factor, electrical conditions, and preconcentration time. Therefore, this research would contribute to the practical understanding of nanoelectrokinetics, providing insight into experimental designs. These findings are expected to offer valuable guidance to researchers aiming to utilize ICP's potential across a spectrum of applications, from purification to preconcentration, in the realm of micro/nanofluidic systems.

Spectroscopic investigations of a commercial graphite screen printed electrode modified by bismuth oxide drop deposition and electrochemical reduction, for cadmium and lead ions simultaneous determination

A single use graphite screen-printed electrode (GSPE) was easily modified, to take advantage of the proven affinity of the nontoxic post-transition metal bismuth (Bi), for metal ions to be detected by Square Wave Anodic Stripping Voltammetry (SWASV). A bismuth oxide (Bi2O3) or a chitosan coated (CS@Bi2O3) nanopowder suspension was drop-casted on the graphite working electrode (WE) surface, giving rise to the precursor of a Bi-modified GSPE. After that, an electrochemical reduction was performed to obtain the Bi– or the CS@Bi–GSPE.X-ray photoelectron spectroscopy and micro-X-ray fluorescence investigations were performed on the graphitic structure pre and post modification. The bismuth oxide deposition amount was considered as critical parameter to sensor performance, indicating a minimum and maximum threshold. Under improved measurement conditions, with a 300 s pre-concentration time, the attained sensors exhibited a linearity in the range (2.0–20.0) μg L−1 in the simultaneous analysis of Pb(II) and Cd(II). The Bi–GSPE showed LODs of 1.7 and 0.5 μg L−1 for Cd(II) and Pb(II) respectively, while 1.5 μg L−1 for Cd(II) and 0.2 μg L−1 for Pb(II) were recorded by the CS@Bi–GSPE. As an applicative proof in real sample, a spike test was carried out in a ground water sample, without any preliminary sample treatment.

Simple, low-cost and sensitive voltammetric detection of homocysteine by using nanocarbon black as electrode material

Generally, the elevated homocysteine (Hcys) degree is easy to cause various diseases, so it is very important to develop suitable method for its quantitative monitoring Because from the unique superiorities (e.g., rapid reaction time and high sensitivity) of the electrochemical technology, several voltammetric sensors have been reported for Hcys detection, but designing more simple, low-cost and sensitive electrochemical sensor for Hcys is still very significant. In this work, just by using a considerable low-cost and readily-accessible nanomaterial, nanocarbon black (CB), as electrode material to detect Hcys for the first time, a very simple, low-cost and sensitive electrochemical sensor for Hcys is fabricated successfully based on CB modify electrode. Via optimizing several key parameters including dropped amount of CB dispersion, preconcentration time of Hcys and pH value of phosphate buffer solution, the as-designed sensor exhibits excellent detection capability coupled with low detection limit (0.003 μM) and wide linearity (0.01–15.0 μM). Furthermore, the repeatability, long-term stability and selectivity as well as real application performances were also evaluated, revealing satisfactory results.

Electrochemical determination of carbendazim in juice samples using carbon composite electrode modified with ion‐exchange resin

AbstractThis work describes a carbon composite modified electrode (CCME) easily prepared using a simple mixture of a commercial cation exchange resin (Amberlite IR 120H) as modifier, graphite powder and paraffin, which was successfully used for spontaneous preconcentration and voltametric determination of carbendazim (CBZ) in juice samples. Parameters such as amount of resin used in the composition of the electrode, pH and preconcentration time as well as instrumental parameters of differential pulse voltammetry (DPV) were studied. Under optimized conditions, the proposed sensor shows to be able to preconcentrate CBZ at an open circuit potential (OCP) condition and presented the highest analytical response in comparison to the unmodified electrode. An analytical curve was obtained for the CBZ determination employing the proposed CCME and showed a linear dynamic range (LDR) between 80.0 nmol L−1 to 2.0 μmol L−1, with a LOD of 19 nmol L−1 and LOQ of 65 nmol L−1. The effect of concomitants on the voltametric response was evaluated by addition and recovery study and a good selectivity was found. The proposed sensor was successfully applied for the determination of CBZ in spiked mango juice samples without any pretreatment.

A flow-batch lab-in-syringe foam microextraction platform for the simultaneous preconcentration and in situ membraneless gas-liquid separation of mercury prior to cold vapor atomic absorption spectrometry

Herein, the proof-of-concept of a novel lab-in-syringe (LIS) foam microextraction platform is presented as a front-end to cold vapor atomic absorption spectrometry (CVAAS) for the simultaneous preconcentration and membraneless gas-liquid separation (GLS) of inorganic mercury in biological samples. The proposed method is based on the on-line formation of the ammonium pyrrolidine dithiocarbamate complex with mercury that was retained in the pores of polyurethane foam immobilized on the piston of the LIS system. Metal complex elution and in situ mercury vapor generation are accomplished inside the microsyringe in a flow-batch format, while the separation of vapor species is achieved via the membraneless GLS found at the top of the syringe’s barrel. Under optimized operation conditions, for 90 s preconcentration time, the limit of detection was 0.02 μg L−1 and the repeatability (RSD) was 3.8% (at the 0.5 μg L−1 concentration level), within a working range extending up to 4.0 μg L−1. The practicality of the novel manifold was demonstrated using the Blue Applicability Grade Index, while the accuracy of the method was evaluated using certified reference materials and spiked samples.

Evaluation of digoxin-boronate ester formation through in-capillary derivatisation-large volume sample stacking-capillary zone electrophoresis.

Determination of digoxin through in-capillary derivatisation based on the formation of o-tolyl- and 2-naphthyl-anionic boronate esters in combination with large volume sample stacking-capillary electrophoresis is proposed. The derivatisation reaction was performed at basic pH values to obtain compounds with a charge and chromophore group during the stacking process. After stacking, the species were separated and detected at 225 nm using p-nitrophenol as an internal standard. Stacking and derivatisation parameters such as pre-concentration time, preconcentration voltage and injection time (relation between the analyte and the derivatisation agent) were evaluated using a Box-Behnken design. Under optimal conditions, the proposed method exhibits a linear range of 1.08-50.00 μM with a limit of detection of 0.36 μM; additionally, adequate repeatability and reproducibility was obtained (%RSD ≤ 5.0%). The methodology was validated by comparing it to an HPLC-UV established methodology and was successfully applied for the determination of digoxin in pharmaceutical tablets and blood serum samples, showing a positive performance for these matrices.

Highly sensitive voltammetric determination of hydrochlorothiazide using a glassy carbon electrode modified with Super P carbon black nanoparticles.

Hydrochlorothiazide is an extremely important diuretic that regulates body functions, which can prevent several diseases. However, the abuse of this diuretic is concerning since it does not require a medical prescription, particularly for aesthetic purposes such as weight loss, which can lead to various health problems, including ventricular arrhythmia. The present work aims to use a glassy carbon electrode modified with Super P carbon black (SPCB/GCE) to quantify hydrochlorothiazide through Linear Sweep Adsorptive Stripping Voltammetry (LSAdSV). The modification of the GCE with SPCB significantly improved the response of hydrochlorothiazide. Furthermore, due to the adsorptive nature of charge transport, applying preconcentration time enhanced sensitivity. The optimized system provided a linear range of 0.5 to 30.0 μmol L-1 with a detection limit of 0.083 μmol L-1. Pharmaceutical tablet analyses indicated approximately 25 mg per tablet, which was confirmed by the UV-vis and in agreement with that indicated by the manufacturer. Furthermore, analyses of the tea, synthetic urine, tap water and lake water samples indicated recovery values close to 100%, demonstrating that there was no matrix effect. Therefore, it is possible to infer that the proposed method together with the sensor modified with carbon black nanoparticles presented excellent results, demonstrating that it can be an alternative method of monitoring this drug in different samples.

Removal of manganese (II) in water samples by the aeration-filtration process and determination based on 5-Br-PADAP ligand by cathodic stripping voltammetry

In this study, manganese (Mn II) was determined in aqueous media by an electrochemical method, and its removal was evaluated using the aeration-filtration process (AFP). An electrochemical sensor based on carbon paste (EPC) modified with the 5-Br-PADAP ligand was used to measure Mn (II) in aqueous media. Through the optimization of analytical parameters in cathodic stripping voltammetry (CSV), real boreholes and well water samples could be analyzed for manganese content. The optimum parameters such as preconcentration potential (1100 mV), preconcentration time (240s), 5-Br-PADAP ligand concentration (20 µmol L-1), and electrode rotation speed during pre-concentration (1000 rpm) were studied and optimized. The detection limit (LOD) is estimated at 3 ´10-7 mol L-1 with a relative standard deviation (RSD) of 3.36%. The real samples showed that some water points have more concentration than the standard. A simple, effective, inexpensive, and rural-friendly method was used for treating manganese-rich water. Following the aeration phase, the sand and gravel column was filtered to remove manganese (II) from the water. The removal efficiency of Mn was obtained at a rate of 74.8- 84.5% and more than 95% after two hours of aeration and 1 hour at pH 8 for real samples.

Determination of α-Naphthol and β-Naphthol in water samples by capillary electrophoresis coupled with large volume sample stacking

ABSTRACT A simple, fast, and efficient on-line pre-concentration based on large volume sample stacking (LVSS-CE) was developed for the determination of α-Naphthol, and β-Naphthol (α-NAP and β-NAP) in complex matrices. Parameters that affect the analytical performance of LVSS were systematically optimised using a Box-Behnken design (injection time, pre-concentration time, and voltage of reverse polarity). Under the optimal conditions of injection time (180 s), pre-concentration time (180 s), and voltage of reverse polarity (−6 kV), the sensitivity was improved 25.9 and 38.8-fold for α-NAP and β-NAP in comparison to CE-UV. The detection limits for α-NAP and β-NAP were 6.56 and 4.63 µg L−1, and the method was successfully applied in drinking and tap water samples with recoveries from 92.98 to 97.46 with RSD less than 10.00% in all cases.

Voltammetric MDMA Analysis of Seized Ecstasy Samples

(1) Background: 3,4-Methylenedioxymethamphetamine (MDMA) is an illicit drug that is sold as ecstasy. We aimed to develop a voltammetric method based on a chemically modified electrode (CME) to analyze MDMA. (2) Methods: The CME was evaluated with respect to the percentage of modifier, pre-concentration time, electroanalytical parameters, and selectivity. Then, the performance of the new voltammetric method was compared to the performance of color tests and chromatographic analyses (GC-MS and UPLC-MS) during the analysis of 11 seized ecstasy batches. (3) Results: The modifier percentage (v/v) of 1.5% provided the best CME. The electroanalytical parameters were in a linear range from 4.06 to 25.42 µmol L−1, SD = 0.018 µA, m = 84.0 × 103 µA L mol−1, r = 0.999, LD = 0.64 µmol L−1, and LQ = 2.17 µmol L−1. The CME was selective for MDMA. The MDMA concentration in the analyzed ecstasy lots ranged from 0 (without MDMA) to 63% (w/w). The voltammetric method developed for quantifying MDMA in ecstasy lots proved feasible and accurate (with a relative percentage error of ≤ ±13.2%). (4) Conclusions: The CME developed herein showed greater sensitivity (m) and lower LD and LQ for quantifying MDMA traces, paving the way for the use of voltammetric methods during forensic investigations.

A continuous flow polyurethane foam solid phase microextraction lab-in-syringe platform for the automatic determination of toxic metals

A novel fully automatic continuous flow polyurethane foam solid phase microextraction lab-in-syringe system for on-line sample preconcentration/separation has been developed as a front-end to flame atomic absorption spectrometry. For the first time lab-in-syringe in continuous flow has been adopted for the determination of toxic metals. The microextraction procedure was performed after on-line metal complexation with ammonium pyrrolidine dithiocarbamate, while the elution was conducted by 400 μL of methyl isobutyl ketone. The main chemical and hydrodynamic factors that affected the performance of the method were optimized using Cd and Pb as model analytes. For 90 s preconcentration time, the limits of the detection were 0.20 and 1.7 μg L−1 for Cd and Pb, respectively, while the enhancement factors were 79 for Cd and 150 for Pb. The relative standard deviation% values were lower than 2.8 % for all analytes. As a proof-of-concept the proposed system was used for environmental water analysis, providing relative recoveries within the range of 94.0 and 104.4 %. The Green Analytical Procedure Index and Blue Applicability Grade Index proved reduced environmental impact and high practicality for the proposed method.

Nanomaterial-based magnetic surface molecularly imprinted polymers for specific extraction and efficient recognition of dibutyl phthalate.

A rapid and selective sorbent for the enrichment of dibutyl phthalate (DBP) from water and Chinese Baijiu samples was established using magnetic surface molecularly imprinted polymers (MSMIPs) combined with gas chromatography-mass spectrometer (GC-MS). The MSMIPs were synthesized using a magnetic nanosphere material with silica layer, increasing the polymer surface area as a carrier. Compared with the traditional methods, the addition of magnetic microspheres simplified the process of food substrate purification and significantly shortened the pre-concentration time. The MSMIPs adsorption conforms to the Freundlich isotherm model as multilayer adsorption on an inhomogeneous surface and the pseudo-second-order model. The developed MSMIPs combined with GC-MS method showed good linearity in DBP concentration range of 0.02-1.0mg L-1 with low LOD (0.0054mg L-1) and LOQ (0.018mg L-1), and obtained good recoveries in real samples (95.2-97.2%) with RSD<5.0% (n=9), which were consistent with those from Chinese national standard method.

Smartphone-based wearable microfluidic electrochemical sensor for on-site monitoring of copper ions in sweat without external driving

The directional movement of liquid without exogenous drive can show great potential in portable electrochemical platforms. Herein, we developed a portable electrochemical platform that drove electrolyte flow by surface tension gradient, which can realize collection of electrolyte, flow preconcentration and electrochemical detection of Cu2+. The induced graphene electrodes (LIG) was fabricated using laser direct writing, and flower cluster shaped ZnO nanorods (FC-ZnONRs) were prepared and modified on LIG, which provided a large amount of space for electrolyte to shuttled between the holes of LIG and ZnO, and increased the electrochemical active sites and electrons transport ability. The effect of surface tension gradients driving fluid flow could accelerate preconcentration, shorten detection time (save 300 s of preconcentration time) and enhance electrochemical responses in synergy with the 3D FC-ZnONRs/LIG. The microfluidic system possessed excellent performance for detection of Cu2+ ranged from 1 μg L−1 to 2100 μg L−1 with a low detection limit (LOD) of 0.0368 μg L−1 and high sensitivity of 0.414 μA (μg L−1)−1 cm−2. Additionally, this portable microfluidic system was successfully worn on the skin for analysing Cu2+ in human sweat, and the results showed good consistency with inductively coupled plasma-mass spectrometry (ICP-MS). This novel sensing system provides a sample collection, rapid detection, low cost and easy-to-operate strategy for heavy metal ions analysis in real samples and shows huge application prospects in point-of-care testing.

In-situ growth of porous rod-like tungsten oxide for electrochemical determination of cupric ion

Preconcentration can effectively enhance the detection performance of electrodes in the electrochemical detection of heavy metal ions, but it also presents challenges for real-time monitoring. Several attempts have been made to optimize preconcentration by improving the adsorption capacity or detection mechanism of the electrode. The valence transfer of tungsten oxide between W5+/W6+ can participate in the reduction between the electrode material and heavy metal ions, playing a role in preconcentration to some extent. Therefore, we developed a WO3/SSM electrochemical sensor for the detection of Cu(II) that utilizes the valence variation property of WO3. The crystallinity and microstructure of the WO3/SSM electrode can be regulated by controlling the deposition parameters, and we prepared three types of WO3/SSM with different morphologies to identify the influence of the electrochemical effective surface area. The proposed electrode shows high performance as a Cu(II) sensor under short preconcentration time (60 s), with an excellent sensitivity of 14.113 μA μM−1 cm−2 for 0.1–10.0 μM and 4.7356 μA μM−1 cm−2 for 10.0–20.0 μM. Overall, the combined effect of morphology and valence transfers shortens the preconcentration time and optimizes preconcentration while ensuring excellent electrode performance. This WO3/SSM electrode is expected to drive great advances in the application of tungsten oxide in the electrochemical detection of heavy metal ions.

Novel synthesized SABA/MWCNTs composite to detect Cd2+ and Pb2+ ions in real samples of rice water, tobacco extract and raw milk

The novel synthesized of salicylidene-2-amino benzyl alcohol (SABA)/multiwalled carbon nanotubes (MWCNTs) modified electrode was implied for the first time for detection of trace quantity of Cd2+ and Pb2+ in the aqueous medium using square wave anodic stripping voltammetry (SWASV). The synthesis of salicylidene-2-amino benzyl alcohol (SABA) was confirmed using Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (H1-NMR). The novel sensor (SABA/MWCNTs) was evaluated using a scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDX). The conductivity of sensors was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The effect of pH, supporting electrolyte and preconcentration time were investigated. Under the optimum conditions, the limits of detection (LODs) range was obtained between 0.02 ng L−1 for Cd2+ and 0.012 ng L−1 for Pb2+ ions. In addition, the developed method was also examined by analysis of Cd2+ and Pb2+ in rice water, tobacco extract and raw milk with good precision and accuracy. Also, the validation is carried out with atomic absorption spectroscopy (AAS).

Glassy Carbon Electrode Modified with CB/TiO2 Layer for Sensitive Determination of Sumatriptan by Means of Voltammetry and Flow Injection Analysis

Sumatriptan is an organic chemical compound from the tryptamine group. It is used as a medicine for migraine attacks and in the treatment of cluster headaches. In this work, a new voltammetric method is proposed for highly sensitive SUM determination, using glassy carbon electrodes modified with carbon black and titanium dioxide suspension. The novelty of the presented work is the usage of the mixture of carbon black and TiO2 as glassy carbon electrode modifier for the first time for SUM determination. The mentioned sensor was characterized by great repeatability and sensitivity of measurements, which resulted in the obtention of a wide range of linearity and a low detection limit. The electrochemical properties of the CB-TiO2/GC sensor was characterized using the LSV and EIS method. The effect of different factors on the SUM peak, such as supporting electrolyte type, preconcentration time and potential, or influence of interferents, were tested using the square wave voltammetry technique. The linear voltammetric response for the analyte was obtained in the concentration range of 5 nmol L−1 to 150 μmol L−1 with a detection limit of 2.9 nmol L−1 for a preconcentration time of 150 s in the 0.1 mol L−1 phosphate buffer pH 6.0. The proposed method was successfully applied for highly sensitive sumatriptan determination in complex matrices, such as tablets, urine, and plasma, with a good recovery parameter (94–105%). The presented CB-TiO2/GC electrode is characterized by great stability, it was used for 6 weeks without significant changes in the SUM peak current. Amperometric and voltammetric measurements of SUM under the flow injection conditions were also performed to indicate the possibility of its fast and accurate determination with a time of single analysis of approx. 30 s.

An investigation of Pseudomonas marincola to determine Pb(II) biosensor potential

Biosensors are strong alternatives to conventional analytical techniques such as HPLC and spectroscopic techniques for water quality and heavy metal detection. Heavy metal contaminated waters can monitor by microbial biosensors efficiently. For this purpose, newly isolated Pseudomonas sp. is used to develop a highly sensitive low-cost microbial biosensor for water quality monitoring. The objective of the study is the invention of new high sensitive low-cost microbial biosensors to determine heavy metals in aqueous solutions and optimise the working conditions Pseudomonas marincola cells were embedded onto the Screen Printed Electrode (SPE) carbon surface and dried for 30 minutes at laminar flow cabinet. Developed microbial sensors were immersed into the Pb(II) solution for electrochemical analysis. After the exposure time, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) analyses were carried out. The study shows that the sensor was found in a linear range between 1x10−8 M and 8x10−8 M, with the lowest detection limit 10−9 M. The optimum pre-concentration time and scan rate were measured as 10 minutes and 10 mV/s, respectively. The results support that the new isolated Pseudomonas sp. has significant potential to determine the trace amount of lead in aqueous solutions.