Determination of naphthenic acids in produced water by using microchip electrophoresis with integrated contactless conductivity detection.

This study reports for the first time the use of a microchip electrophoresis (ME) device with integrated capacitively coupled contactless conductivity detection (C4D) to analyze naphthenic acids in produced water. A mixture containing 9-anthracenecarboxylic, 1-naphthoic, and benzoic acids was separated and detected using a running buffer composed of 10 mmol L-1 carbonate buffer (pH = 10.2). The separation was achieved within ca. 140 s with baseline resolution greater than 2 and efficiency values ranging from 1.9 × 105 to 2.4 × 105 plates m-1. The developed methodology provided linear correlation with determination coefficients greater than 0.992 for the concentration ranges between 50 and 250 µmol L-1 for benzoic and 9-anthracenecarboxylic acids, and between 50 and 200 µmol L-1 for 1-naphthoic acid. The achieved limit of detection values varied between 4.7 and 7.7 µmol L-1. The proposed methodology revealed satisfactory repeatability with RSD values for a sequence of eight injections between 5.5 and 7.7% for peak areas and lower than 1% for migration times. In addition, inter-day precision was evaluated for sixteen injections (a sequence of four injections performed during four days), and the RSD values were lower than 11.5 and 4.9% for peak areas and migration time, respectively. Five produced water samples were analyzed, and it was possible to detect and quantify 9-anthracenecarboxylic acid. The concentrations ranged from 1.05 to 2.24 mmol L-1 with recovery values between 90.8 and 96.0%. ME-C4D demonstrated satisfactory analytical performance for determining naphthenic acids in produced water for the first time, which is useful for petroleum or oil industry investigation.

Determination of acetylcholinesterase and α-glucosidase inhibition by electrophoretically-mediated microanalysis and phenolic profile by HPLC-ESI-MS/MS of fruit juices from Brazilian Myrtaceae Plinia cauliflora (Mart.) Kausel and Eugenia uniflora L.

Alzheimer's disease and diabetes mellitus are contemporary diseases of great concern. Phenolic compounds are linked to several health benefits and could lead to novel strategies to combat these ailments. The objective of this study was to evaluate by electrophoretically-mediated microanalysis the potential inhibitory activity of the fruit juices from Plinia cauliflora ("jaboticaba") and Eugenia uniflora ("pitanga") toward acetylcholinesterase (AChE) and α-glucosidase, target enzymes in strategies for the treatment of these diseases. The phenolic profiles of the samples were also investigated. Jaboticaba and pitanga juices inhibited 85.90 ± 1.73 and 52.67 ± 1.24% of AChE activity at 5 mg mL-1, and 57.91 ± 2.60 and 69.47 ± 2.89% of α-glucosidase activity at 1 mg mL-1, respectively. Total phenolic content of the juices were 303.54 ± 28.28 and 367.00 ± 11.42 mgGA L-1, respectively. The observed inhibitory activity can be explained, at least in part, by the presence of the phenolic compounds.

Nonaqueous electrophoresis on microchips: A review.

The use of organic solvents as electrolytic medium in electrophoresis has become an important alternative for the analysis of compounds that exhibit low or no solubility in water. In recent years, nonaqueous electrophoresis has been extensively explored in conventional capillary systems for different applications. On the other hand, this separation strategy is still not as popular as free solution electrophoresis on chip-based platforms due to the effects of solvent in the background electrolyte on the sample injection, detection performance, and microfluidic platform compatibility. In this way, this review summarizes the main achievements on nonaqueous microchip electrophoresis (NAME). To the best of our knowledge, this is the first review dedicated to discuss exclusively nonaqueous electrophoresis on chip-based systems. For this purpose, some important theoretical aspects involved when separations are performed in organic medium, such as equilibrium, interactions and electrophoretic considerations, are included in the review. In addition, the main challenges, advantages and influences of nonaqueous media on the sample injection, detection as well as the choice of the substrate to fabricate chip-based electrophoresis devices are highlighted. Last, examples showing the feasibility of nonaqueous microchip electrophoresis for applications exploiting different methodologies, operational, and instrumental conditions are summarized and discussed. We hope this review can be useful to spread the huge potential of nonaqueous electrophoresis on microfluidic platforms.

Rapid and inexpensive method for the simple fabrication of PDMS-based electrochemical sensors for detection in microfluidic devices.

The fabrication of PDMS microfluidic structures through soft lithography is widely reported. While this well-established method gives high precision microstructures and has been successfully used for many researchers, it often requires sophisticated instrumentation and expensive materials such as clean room facilities and photoresists. Thus, we present here a simple protocol that allows the rapid molding of simple linear microchannels in PDMS substrates aiming microfluidics-based applications. It might serve as an alternative to researchers that do not have access to sophisticated facilities such as clean rooms. The method developed here consists on the use of pencil graphite leads as template for the molding of PDMS channels. It yields structures that can be used for several applications, such as housing support for electrochemical sensors or channels for flow devices. Here, the microdevices produced through this protocol were employed for the accommodation of carbon black paste, which was utilized for the first time as amperometric sensor in microchip electrophoresis. This platform was successfully used for the separation and detection of model analytes. Ascorbic acid and iodide were separated within 45 s with peak resolution of 1.2 and sensitivities of 198 and 492 pA/µM, respectively. The background noise was ca. 84 pA. The analytical usefulness of the system developed was successfully tested through the quantification of iodide in commercial pharmaceutical formulations. It demonstrates good efficiency of the microfabrication protocol developed and enables its use for the easy and rapid prototyping of PDMS structures over a low fabrication cost.

Separation of carbohydrates on electrophoresis microchips with controlled electrolysis.

This study reports the separation of fructose, galactose, glucose, lactose and sucrose on glass microchip electrophoresis (ME) devices using a microfluidic platform adapted with external reservoirs for controlling the electrolysis phenomenon. The connections between external reservoirs and microfluidic platform were performed by saline bridges created using silicone tubing filled with BGE. The separation conditions were optimized and the best results were achieved using a BGE containing 75 mmol/L NaOH and 15 mmol/L trisodium phosphate. Electrophoretic separations were monitored using a capacitively coupled contactless conductivity detection system. The controlled electrolysis has successfully allowed the application of a higher voltage on the separation channel promoting the baseline separation of five carbohydrates within 180 s with great run-to-run repeatability (RSD < 1%). The achieved efficiencies ranged from 45 000 ± 6000 to 70 000 ± 3000 plates/m demonstrating a performance better than ME devices without controlled electrolysis. The proposed system offered good linearity from 1 to 10 mmol/L and LODs between 150 and 740 µmol/L. The use of external tubes for controlling the electrolysis phenomenon on ME devices has solved common problems associated to run-to-run repeatability and analytical reliability required for routine and quantitative analysis.

Microchip Electrophoresis Containing Electrodes for Integrated Electrochemical Detection.

Microchip electrophoresis is a versatile separation technique. Electrochemical detection is suitable to apply to microdevices due to its easy integration to the fabrication process and good sensitivity and selectivity. Here we describe the procedures to prepare Pt band electrodes deposited on glass to couple to polydimethylsiloxane (PDMS) microchips aiming the separation and detection of nitrite using an isolated potentiostat.

Paper-Based Electrophoresis Microchip as a Powerful Tool for Bioanalytical Applications.

This chapter describes the development of paper-based microchip electrophoresis (pME) devices for the separation of clinically relevant compounds. pME were fabricated by laser cut and thermal lamination process using polyester pouches. In addition, hand-drawn pencil electrodes were integrated to the device to perform capacitively coupled contactless conductivity detection (C4D). Finished device costs less than US$ 0.10 and did not require either sophisticated instrumentation or clean room facilities. Furthermore, pME is lightweight, easy to handle, flexible, and robust. pME-C4D device revealed an excellent capacity to separate BSA and creatinine in less than 150 s with baseline resolution. The device proposed in this chapter has proven to be a good alternative as a platform for the diagnosis of diseases from renal disorders such as diabetes mellitus and heart disease.

Microchip Electrophoresis Tools for the Analysis of Small Molecules.

Microchip electrophoresis (ME) results from miniaturization of capillary electrophoresis (CE) to a microfabricated separation device. Both techniques have common characteristics, but in some aspects, the microfluidic separation device has unique features resulting from its planar miniaturized format. Here we describe the process to transfer of CE to ME and the benefits and drawbacks of the chip with respect to the capillary. A practical guide for method development on the microchip for small ionizable molecules such as phenolic compounds, amino acids, or alkaloids is also presented.

Rapid separation of post-blast explosive residues on glass electrophoresis microchips.

This study describes the development of an analytical methodology based on the use of microchip electrophoresis (ME) devices integrated with capacitively coupled contactless conductivity detection (C4 D) for the separation and detection of inorganic anions in post-blast explosive residues. The best separation condition was achieved using a running buffer composed of 35 mmol/L lactic acid, 10 mmol/L histidine and 0.070 mmol/L cetyl(trimethyl ammonium) bromide. For C4 D measurements, the highest sensitivity was obtained applying a 700 kHz sinusoidal wave with excitation voltage of 20 Vpp . The separation of Cl- , NO3- , NO2- , SO42- , ClO4- and ClO3- was performed within ca. 150 s with baseline resolution and efficiencies between 4.4 × 104 and 1.7 × 105 plates/m. The found limits of detection ranged between 2.5 and 9.5 µmol/L. Last, real samples of post-blast explosive residues were analyzed on the ME-C4 D devices obtaining successfully the determination of Cl- , NO3- and SO42- . The achieved concentration values varied between 12.8-72.5 mg/L for Cl- , 1.7-293.1 mg/L for NO3- and 1.3-201.3 mg/L for SO42- . The data obtained using ME-C4 D devices were in good agreement with the concentrations found by ion chromatography. The approach reported herein has provided short analysis time, instrumental simplicity, good analytical performance and low cost. Furthermore, the ME-C4 D devices emerge as a powerful and portable analytical platform for on-site analysis demonstrating to be a promising tool for the crime scene investigation.

Portable analytical platforms for forensic chemistry: A review.

This current review article focuses on recent contributions to on-site forensic investigations. Portable and potentially portable methods are presented and critically discussed about (bio)chemical trace analysis and studies performed outside the controlled laboratory environment to rapidly help in crime scene inquiries or forensic intelligence purposes. A wide range of approaches including electrochemical sensors, microchip electrophoresis, ambient ionization on portable mass spectrometers, handheld Raman and NIR instruments as well as and point-of-need devices, like paper-based platforms, for in-field analysis of latent evidences, controlled substances, drug screening, hazards, and others to assist in law enforcements and solving crime more efficiently are highlighted. The covered examples have successfully demonstrated the huge potential of portable devices for on-site applications. Future investigations should consider analytical validation to compete equality and even replace current gold standard methods.

Screening of seized cocaine samples using electrophoresis microchips with integrated contactless conductivity detection.

This study describes the development of a new analytical method for the separation and detection of cocaine (COC) and its adulterants, or cutting agents, using microchip electrophoresis (ME) devices coupled with capacitively coupled contactless conductivity detection (C4 D). All the experiments were carried out using a glass commercial ME device containing two pairs of integrated sensing electrodes. The running buffer composed of 20 mmol/L amino-2-(hydroxymethyl) propane-1,3-diol and 10 mmol/L 3,4-dimethoxycinnamic acid provided the best separation conditions for COC and its adulterants with baseline resolution (R > 1.6), separation efficiencies ranging from (2.9 ± 0.1) to (3.2 ± 0.2) × 105 plates/m, and estimated LOD values between 40 and 150 µmol/L. The quantification of COC was successfully performed in four samples seized by the Brazilian Federal Police Department and all predicted values agree with values estimated by the reference method. Some other interfering species were detected in the seized samples during the screening procedure on ME-C4 D devices. While lidocaine was detected in sample 3, the presence of levamisole was observed in samples 2 and 4. However, their concentrations were estimated to be below the LOQ. ME-C4 D devices have proved to be quite efficient for the identification and quantification of COC with errors lower than 10% when compared to the data obtained by a reference method. The approach herein reported offers great potential to be used for on-site COC screening in seized samples.

Pencil graphite leads as simple amperometric sensors for microchip electrophoresis.

In this work we demonstrate, for the first time, the use of inexpensive commercial pencil graphite leads as simple amperometric sensors for microchip electrophoresis. A PDMS support containing one channel was fabricated through soft lithography and sanded pencil graphite leads were inserted into this channel to be used as working electrodes. The electrochemical and morphological characterization of the sensor was carried out. The graphite electrode was coupled to PDMS microchips in end-channel configuration and electrophoretic experiments were performed using nitrite and ascorbate as probe analytes. The analytes were successfully separated and detected in well-defined peaks with satisfactory resolution using the microfluidic platform proposed. The repeatability of the pencil graphite electrode was satisfactory (RSD values of 1.6% for nitrite and 12.3% for ascorbate, regarding the peak currents) and its lifetime was estimated to be ca. 700 electrophoretic runs over a cost of ca. $ 0.05 per electrode. The limits of detection achieved with this system were 2.8 µM for nitrite and 5.7 µM for ascorbate. For proof of principle, the pencil graphite electrode was employed for the real analysis of well water samples and nitrite was successfully quantified at levels below its maximum contaminant level established in Brazil and US.

Recent applications of nanomaterials in capillary electrophoresis.

Nanomaterials have found an important place in Analytical Chemistry and, in particular, in Separation Science. Among them, metal-organic frameworks, magnetic and non-magnetic nanoparticles, carbon nanotubes and graphene, as well as their combinations, are the most important nanomaterials that have been used up to now. Concerning capillary electromigration techniques, these nanomaterials have also been used as both pseudostationary phases in electrokinetic chromatography (EKC) and as stationary phases in microchip capillary electrophoresis (CE) and capillary electrochromatography (CEC), as a result of their interesting and particular properties. This review article pretends to provide a general and critical revision of the most recent applications of nanomaterials in this field (period 2010-2017).

High performance separation of quaternary amines using microchip non-aqueous electrophoresis coupled with contactless conductivity detection.

This study describes the development of an analytical methodology for the separation of quaternary amines using non-aqueous microchip electrophoresis (NAME) coupled with capacitively coupled contactless conductivity detection (C4D). All experiments were performed using a commercial microchip electrophoresis system consisting of a C4D detector, a high-voltage sequencer and a microfluidic platform to assemble a glass microchip with integrated sensing electrodes. The detection parameters were optimized and the best response was reached applying a 700-kHz sinusoidal wave with 14Vpp excitation voltage. The running electrolyte composition was optimized aiming to achieve the best analytical performance. The mixture containing methanol and acetonitrile at the proportion of 90:10 (v:v) as well as sodium deoxycholate provided separations of ten quaternary amines with high efficiency and baseline resolution. The separation efficiencies ranged from 8.7×104 to 3.0×105 plates/m. The proposed methodology provided linear response in the concentration range between 50 and 1000µmol/L and limits of detection between 2 and 27µmol/L. The analytical feasibility of the proposed methodology was tested in the determination of quaternary amines in corrosion inhibitor samples often used for coating oil pipelines. Five quaternary amines (dodecyltrimethylammonium chloride, tetradecyltrimetylammonium bromide, cetyltrimethylammonium bromide, tetraoctylammonium bromide and tetradodecylammonium bromide) were successfully detected at concentration levels from 0.07 to 6.45mol/L. The accuracy of the developed methodology was investigated and the achieved recovery values varied from 85 to 122%. Based on the reported data, NAME-C4D devices exhibited great potential to provide high performance separations of hydrophobic compounds. The developed methodology can be useful for the analysis of species that usually present strong adsorption on the channel inner walls.

Hydrodynamic injection on electrophoresis microchips using an electronic micropipette.

Here we report for the first time the use of an electronic micropipette as hydrodynamic (HD) injector for microchip electrophoresis (ME) devices. The micropipette was directly coupled to a PDMS device, which had been fabricated in a simple cross format with two auxiliary channels for sample volume splitting. Sample flow during the injection procedure was controlled in automatic dispenser mode using a volume of 0.6µL. Channel width and device configuration were optimized and the best results were achieved using a simple cross layout containing two auxiliary channels with 300µm width for sample splitting. The performance of the HD injector was evaluated using a model mixture of high-mobility cationic species. The results obtained were compared to the data obtained via electrokinetic (EK) injection. Overall, the HD provided better analytical performance in terms of resolution and injection-to-injection repeatability. The relative standard deviation (RSD) values for peak intensities were lower than 5% (n=10) when the micropipette was employed. In comparison with EK injection, the use of the proposed HD injector revealed an unbiased profile for a mixture containing K+ and Li+(300 µmol L-1 each) over various buffer concentrations. For EK injection, the peak areas decreased from 2.92 ± 0.20-0.72 ± 0.14Vs for K+ and from 1.30 ± 0.10-0.38 ± 0.10Vs for Li+ when the running buffer increased from 20 to 50mmolL-1. For HD injection, the peak areas for K+ and Li+ exhibited average values of 2.48±0.07 and 2.10±0.06Vs, respectively. The limits of detection (LDs) for K+, Na+ and Li+ ranged from 18 to 23µmolL-1. HD injection through an electronic micropipette allows to automatically dispense a bias-free amount of sample inside microchannels with acceptable repeatability. The proposed approach also exhibited instrumental simplicity, portability and minimal microfabrication requirements.

Simple, rapid and, cost-effective fabrication of PDMS electrophoresis microchips using poly(vinyl acetate) as photoresist master.

This study describes a simple, rapid, and cost-effective fabrication of PDMS electrophoresis microchips using poly(vinyl acetate) (PVAc) emulsion as photoresist master. High-relief microfluidic structures were defined on poly(vinyl acetate) previously deposited on printed circuit boards surfaces without cleanroom facilities and sophisticated instrumentation. After a UV exposure, channels with heights ranging from 30 to 140 µm were obtained by controlling the emulsion mass deposited on the master surface. The developing stage was performed using water rather than the organic solvents that are applied for conventional masks. The surface morphology was characterized by optical imaging, profilometry, and SEM. Based on the achieved results, the proposed method offers suitable reproducibility for the prototyping of electrophoresis microchips in PDMS. The feasibility of the resulting PDMS electrophoresis chips was successfully demonstrated with the separation of major inorganic cations within 100 s using a contactless conductivity detection system. The separation efficiencies ranged from ca. 67 900 to 125 600 plates/m. Due to the satisfactory performance and simplified instrumentation, we believe this fabrication protocol presents potential to be implemented in any chemical, biochemical, or biological laboratory.

Authenticity screening of seized whiskey samples using electrophoresis microchips coupled with contactless conductivity detection.

This report describes for the first time the use of microchip electrophoresis (ME) devices integrated with capacitively coupled contactless conductivity detection (C4 D) to investigate the authenticity of seized whiskey samples, which were probably adulterated by simple dilution with tap water. The proposed microfluidic platform was explored for the monitoring of anionic species (Cl- and F- ) in both original and tampered samples. The best separations were achieved within 70 s using a running buffer composed of lactic acid and histidine (pH = 5.9). ME-C4 D devices were used to analyze samples from three different brands (five samples each). Based on the presence of inorganic anions like Cl- , F- , SO42- and NO2- in different amounts, the authenticity of seized whiskeys was compared to original samples. According to the reported data, the proposed microfluidic platform can be useful to help regulatory authorities in the investigation and monitoring of authenticity of commercialized whiskey beverages.

Microchip electrophoresis for wine analysis.

The present critical review provides a summary of representative articles describing the analysis of wine by microchip electrophoresis. Special emphasis has been given to those compounds able to provide background information to achieve the differentiation of wines according to botanical origin, provenance, vintage and quality or assure wine authentication. This review focuses on capillary electrophoresis (CE) microchips dedicated to the analysis of wine covering all the contributions concerning this area. The most relevant compounds in wine analysis such as phenols, organic acids, inorganic species, aldehydes, sugars, alcohols, and neuroactive amines were considered. Moreover, a special section is dedicated to the potential of CE microchip for wine classification. Indeed, potential directions for the future are discussed.

Hand drawing of pencil electrodes on paper platforms for contactless conductivity detection of inorganic cations in human tear samples using electrophoresis chips.

This paper describes for the first time the fabrication of pencil drawn electrodes (PDE) on paper platforms for capacitively coupled contactless conductivity detection (C(4) D) on electrophoresis microchips. PDE-C(4) D devices were attached on PMMA electrophoresis chips and used for detection of K(+) and Na(+) in human tear samples. PDE-C(4) D devices were produced on office paper and chromatographic paper platforms and their performance were thoroughly investigated using a model mixture containing K(+) , Na(+) , and Li(+) . In comparison with chromatographic paper, PDE-C(4) D fabricated on office paper has exhibited better performance due to its higher electrical conductivity. Furthermore, the detector response was similar to that recorded with electrodes prepared with copper adhesive tape. The fabrication of PDE-C(4) D on office paper has offered great advantages including extremely low cost (< $ 0.004 per unit), reduced fabrication time (< 5 min), and minimal instrumentation (pencil and paper). The proposed electrodes demonstrated excellent analytical performance with good reproducibility. For an inter-PDE comparison (n = 7), the RSD values for migration time, peak area, and separation efficiency were lower than 2.5, 10.5, and 14%, respectively. The LOD's achieved for K(+) , Na(+) , and Li(+) were 4.9, 6.8, and 9.0 µM, respectively. The clinical feasibility of the proposed approach was successfully demonstrated with the quantitative analysis of K(+) and Na(+) in tear samples. The concentration levels found for K(+) and Na(+) were, respectively, 20.8 ± 0.1 mM and 101.2 ± 0.1 mM for sample #1, and 20.4 ± 0.1 mM and 111.4 ± 0.1 mM for sample #2.

Electrodeposition of reduced graphene oxide on a Pt electrode and its use as amperometric sensor in microchip electrophoresis.

This report describes the development and application of a novel graphene-modified electrode to be used as amperometric sensor in microchip electrophoresis (ME) devices. The modified electrode was achieved based on electroreduction of graphene oxide on an integrated Pt working electrode of a commercial ME device. The surface modification was characterized by SEM and cyclic voltammetry techniques. The results indicated that graphene sheets were successfully deposited exhibiting higher surface conductivity and greater electrode sensitivity. The performance of the modified electrode for the amperometric detection on ME devices has been demonstrated by the separation and detection of an anionic mixture containing iodide and ascorbate. The graphene-modified electrode provided significantly higher sensitivity (896.7 vs. 210.9 pA/µM for iodide and 217.8 vs. 127.8 pA/µM for ascorbate), better separation efficiencies (3400 vs. 700 plates/m for iodide and 10 000 vs. 2400 plates/m for ascorbate), enhanced peak resolutions (1.6 vs. 1.0), and LODs (1.5 vs. 5.3 µM for iodide and 3.1 vs. 7.3 µM for ascorbate) in comparison with the unmodified Pt electrode. The proposed amperometric sensor was successfully applied for the analysis of ascorbic acid (through its anionic form) in a commercial medicine sample, and the results achieved were in agreement with the value provided by the supplier. Based on the data here presented, the modified graphene electrode shows great promise for ME applications.