Performance Of Glassy Carbon Electrode Research Articles

Unlocking the electrochemical performance of glassy carbon electrodes by surface engineered, sustainable chitosan membranes

Chitosan coatings, derived from crustacean shell waste, possess inherent biocompatibility and biodegradability, rendering them suitable for various biomedical and environmental applications, including electrochemical biosensing. Its amine and hydroxyl functional groups offer abundant sites for chemical modifications to boost the charge transfer kinetics and provide excellent adhesion, enabling the construction of robust electrode-coating interfaces for electroanalysis. This study explores the role of electrostatically-driven chemical interactions and crosslinking density originating from different chitosan (Cs) and glutaraldehyde (Ga) concentrations in this aspect. Studying anionic ([Fe(CN)6]3−/4−), neutral (FcDM0/+), and cationic ([Ru(NH3)6]2+/3+) redox probes highlights the influence of Coulombic interactions with chitosan chains containing positively-charged pathways, calculated by DFT analysis. Our study reveals how a proper Ch-to-Ga ratio has a superior influence on the cross-linking efficacy and resultant charge transfer kinetics, which is primarily boosted by up to 20× analyte preconcentration increase, due to electrostatically-driven migration of negatively charged ferrocyanide ions toward positively charged chitosan hydrogel. Notably the surface engineering approach allows for a two-orders of magnitude enhancement in [Fe(CN)6]4− limit of detection, from 0.1 µM for bare GCE down to even 0.2 nM upon an adequate hydrogel modification.

Natural deep eutectic solvent: A novelty alternative as multi-walled carbon nanotubes dispersing agent for the determination of paracetamol in urine.

This work reports for the first time the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multi-wall carboxylated carbon nanotubes (MWCNTs-COOH) using a mixture of a natural deep eutectic solvent (NADES - LGH/lactic acid-glucose-water), ethylene glycol (EG) and water (GCE/MWCNT-LGH-EG) for the determination and N-(4-hydroxyphenyl) acetamide (paracetamol) (APAP) in urine samples. The optimization of both dispersion and measurement conditions was carried out using experimental design. The modified electrode exhibited enhanced current responses, demonstrating excellent electrochemical response towards APAP oxidation compared to MWCNTs-LGH, MWCNTs-EG, MWCNTs-H2O-EtOH and MWCNTs-H2O. The linear dependence between the anodic peak currents and the square root of scan rates over the range of 0.010-0.300 Vs-1 demonstrates that the electro oxidation of APAP occurs under diffusional control. The MWCNT-LGH-EG modified GCE displayed an analytical sensitivity of 10.72mLμg-1 (r=0.9994) and a detection limit of 100ngmL-1 for the selective determination of APAP in urine samples. The proposed electrochemical sensor was successfully applied for quantifying APAP in urine samples in the presence of uric acid. In addition, the accuracy and precision of the method was contrasted against a HPLC reference method.

Ultrasensitive multiwall carbon nanotube-mesoporous MCM-41 hybrid-based platform for the electrochemical detection of ascorbic acid.

This work presents for the first time the systematic preparation of a novel carbon nanotube-MCM-41 hybrid employing the mesoporous material MCM-41 as a successful dispersant for multiwall carbon nanotubes (MWCNTs). Relevant dispersion variables such as the amount of MWCNTs, MCM-41 concentration, and sonication time were optimized through a central composite design (CDD)/response surface methodology (RSM). Several solvents were evaluated and N,N-dimethylformamide (DMF) was selected because it allowed reaching stable dispersions with very good electrochemical response. The electrochemical performance of glassy carbon electrodes (GCE) modified with different hybrids was evaluated by cyclic voltammetry (CV) using ascorbic acid (AA) as redox marker, while their surface morphology was characterized by SEM microscopy. The optimal MWCNT-MCM-41 dispersion condition was 0.75 mg mL-1 MWCNTs, 0.25 mg mL-1 MCM-41, and 30 min sonication. Both, electrochemical results and SEM images correlate with a percolation behavior from MWCNT-MCM-41 hybrid. Electrooxidation of AA at GCE modified with the optimal hybrid occurred under diffusion control and exhibited an enhanced current response (65 μA) and a lower overvoltage (-0.005 V) compared to bare GCE (ip = 22 μA, Ep = 0.255 V). The amperometric response of AA at GCE/MWCNT-MCM-41 exhibited remarkable figures of merit, including an ultralow detection limit (1.5 nM), high sensitivity (45.4 × 103 μA M-1), excellent short- and long-term stability, and very good anti-interference ability for AA detection. The analytical applicability of the developed electrochemical sensor was evaluated by sensing AA in several real samples, showing excellent correlation with the values reported by manufacturers in both pharmaceutical and food samples.

Highly sensitive detection of Pb2+ and Cu2+ based on ZIF-67/MWCNT/Nafion-modified glassy carbon electrode

A series of different facile modification layers (MLs) was designed to gradually increase the electrochemical sensing performance of glassy carbon electrode (GCE) for simultaneously detecting Pb2+ and Cu2+. ML designs were mainly a different combination of ZIF-67, MWCNT and Nafion, and their different electrochemical sensing performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave stripping voltammetry (SWSV) and chronocoulometry. The fabricated sensor, which modified with ZIF-67/MWCNT and Nafion layer, exhibited the biggest response peak current to Pb2+ and Cu2+. In addition, it displayed a wide linear detection range of 1.38 nM–5 μM for Pb2+ and 1.26 nM–5 μM for Cu2+, a detection accuracy of about 1 nM for both Pb2+ and Cu2+, and an excellent stability for both Pb2+ and Cu2+. We also analyzed the real water sample taken from Changchun’s Sanjia Lake and Yan Lake. We believe this ML design provides instruction for building high-performance electrochemical sensing systems.

Effect of Anodic Pretreatment on the Performance of Glassy Carbon Electrode in Acetonitrile and Electrooxidation of Para-substituted Phenols in Acetonitrile on Platinum and Glassy Carbon Electrode

In the first part of the work electropolymerisation of phenol was studied at glassy carbon electrode. Rapid fouling of its surface indicated the formation of coherent poly(phenyleneoxide) layer which was demonstrated by the repeated cyclic voltammetric scans. Effect of anodic pretreatment potential in acetonitrile solvent was also investigated and the results showed that at potentials higher than 2 V glassy carbon electrode becomes deactivated. Preanodisation of glassy carbon electrode at 3 V in acetonitrile resulted in diminished anodic peak currents by phenols. It was due to the partial deactivation of electrode surface and its extent increased with the pretreatment time. The electrooxidation of para-substituted phenols (p-Cl-phenol, p-NO2-phenol, p-tertbutylphenol, p-methoxyphenol) in acetonitrile resulted in no fouling layer on platinum electrode and the peak currents were significantly higher than in the first scan of unsubstituted phenol in the same concentration. Glassy carbon deactivated continuously by repeating the scans due to the solvent and bonding of products on the surface.

Mercury‐modified Lignosulfonate‐stabilized Gold Nanoparticles as an Alternative Material for Anodic Stripping Voltammetry of Thallium

AbstractLignosulfonate‐stabilized gold nanoparticles (AuNPs‐LS) were synthesized and subsequently used as a complexing agent for mercury ions. The obtained AuNPs‐LS/Hg2+ complex was characterized by means of various physicochemical techniques such as UV‐vis spectroscopy, transmission electron microscopy and cyclic voltammetry. Furthermore, the resulting complex was evaluated as an electrode modifier for the development of amperometric sensors. Upon sufficient negative potential, the bound mercury ions are reduced to form an amalgam with AuNPs‐LS. Thus, the performance of glassy carbon electrode (GCE) modified by AuNPs‐LS/Hg film was investigated as an electrochemical sensor in the determination of Tl+ ions in a 0.05 M EDTA at pH 4.5. The presence of the mercury containing film improves the analyte accumulation due to its ability to form a fused amalgam with thallium. The presented data indicate that the GCE/AuNPs‐LS/Hg modified electrode shows better performance toward Tl+ determination in comparison to bare GCE. The stripping anodic peak current of thallium was linear over its concentration range from 1.7⋅10−7 to 5.0⋅10−6 M. The detection limit (3σ) was estimated to be 1.4⋅10−7 M. The proposed method was successfully applied for the determination of thallium ions in real samples of soil derived from the area of the copper smelter near Głogów (Poland).

Electrochemical reduction of nalidixic acid at glassy carbon electrode modified with multi-walled carbon nanotubes

The aqueous phase electrochemical degradation of nalidixic acid (NAL) is studied in this work, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as instrumental techniques. The promotional effect of multi-walled carbon nanotubes (MWCNT) on the performance of glassy carbon electrodes is demonstrated, being observed that these materials catalyze the NAL reduction. The effect of surface functional groups on MWCNT −MWCNT-COOH and MWCNT-NH2–was also studied. The modification of glassy carbon electrode (GCE) with MWCNT leads to an improved performance for NAL reduction following the order of MWCNT>MWCNT-NH2>MWCNT-COOH. The best behavior at MWCNT-GCE is mainly due to both the increased electrode active area and the enhanced MWCNT adsorption properties.The NAL degradation was carried out under optimal conditions (pH=5.0, deposition time=20s and volume of MWCNT=10μL) using MWCNT-GCE obtaining an irreversible reduction of NAL to less toxic products. Paramaters as the number of DPV cycles and the volume/area (V/A) ratio were optimized for maximize pollutant degradation. It was observed that after 15 DPV scans and V/A=8, a complete reduction was obtained, obtaining two sub-products identified by liquid chromatography-mass spectrometry (LC–MS).

Covalent functionalization of single-walled carbon nanotubes with polytyrosine: Characterization and analytical applications for the sensitive quantification of polyphenols

This work reports the synthesis and characterization of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr); the critical analysis of the experimental conditions to obtain the efficient dispersion of the modified carbon nanotubes; and the analytical performance of glassy carbon electrodes (GCE) modified with the dispersion (GCE/SWCNT-Polytyr) for the highly sensitive quantification of polyphenols. Under the optimal conditions, the calibration plot for the amperometric response of gallic acid (GA) shows a linear range between 5.0 × 10−7 and 1.7 × 10−4 M, with a sensitivity of (518 ± 5) m AM−1 cm−2, and a detection limit of 8.8 nM. The proposed sensor was successfully used for the determination of total polyphenolic content in tea extracts.

Electrochemical sensor for amino acids and glucose based on glassy carbon electrodes modified with multi-walled carbon nanotubes and copper microparticles dispersed in polyethylenimine

This work reports the analytical performance of glassy carbon electrodes (GCE) modified with multi-walled carbon nanotubes (CNT) and copper microparticles dispersed in polyethylenimine (PEI) (GCE/CNT-PEI-Cu) for the quantification of amino acids, albumin and glucose. The best analytical performance was obtained with CNT-PEI-Cu prepared by sonicating for 15.0min a mixture of 1.0mgmL−1 PEI, 1.0mgmL−1 CNT and 3.0mgmL−1 copper microparticles. In the case of amino acids and albumin, the analytical signals were obtained from the increase of the copper oxidation signal produced as a consequence of the complex formation between Cu(II) and the amino acids. The sensor allowed the highly sensitive (submicromolar levels) and reproducible (3.9%) amperometric quantification of histidine, serine and cysteine at very low potentials (0.000V) and pH7.40. Albumin was quantified by Square Wave Voltammetry after 10.0min interaction at −0.100V with detection limits of 1.2mgmL−1.GCE/CNT-PEI-Cu was also used for the quantification of glucose by amperometry at 0.700V in a 0.100M sodium hydroxide solution through the known catalytic activity of copper towards the oxidation of glucose, with highly competitive detection limits (182nM). GCE/CNT-PEI-Cu was successfully used for the quantification of amino acids and albumin in pharmaceutical products and carbohydrates in beverages.

A voltammetric sensor based on the glassy carbon electrode modified with multi-walled carbon nanotube/poly(pyrocatechol violet)/bismuth film for determination of cadmium and lead as environmental pollutants

The performance of glassy carbon electrodes (GCE) coated with multi-walled carbon nanotube poly(pyrocatechol violet) composite and bismuth film was investigated as an electrochemical sensor in the simultaneous determination of Cd2+ and Pb2+ ions in a 0.1M acetate buffer solution at pH=5.0. The presence of the bismuth film improves the analyte accumulation due to its ability to form a fused alloy with cadmium and lead. It was found that the Bi-film modified electrode shows a better performance than the bare GCE, GCE-MWCNT and GCE-MWCNT/poly(PCV) electrodes. The parameters affecting the stripping current response were investigated and optimized. Under optimal conditions, the electrode showed a good linear response to Cd2+ and Pb2+ in the concentration range of 1.0–300.0μgL−1 and 1.0–200.0μgL−1, respectively. The detection limits were 0.20μgL−1 and 0.40μgL−1 for Cd2+ and Pb2+, respectively. It was found that the sensor has least interference from most of the common ions due to specific and selective interaction of the modifier functionalities with lead and cadmium ions. The response of the electrode remained constant for at least 3 weeks of successive operation. The proposed method was applied for simultaneous determining Cd2+ and Pb2+ contents in water samples.

Single‐Wall Carbon Nanotubes Covalently Functionalized with Polylysine: Synthesis, Characterization and Analytical Applications for the Development of Electrochemical (Bio)Sensors

AbstractThis work reports the synthesis of single‐wall carbon nanotubes (SWCNT) covalently functionalized with polylysine (Plys) and the analytical performance of glassy carbon electrodes (GCE) modified with this material (GCE/SWCNT‐Plys). The resulting electrodes showed an important decrease in the overvoltages for the oxidation of ascorbic acid, uric acid and hydrogen peroxide as well as for the reduction of hydrogen peroxide. The favorable interaction of glucose oxidase (GOx) with SWCNT‐Plys allowed the sensitive and selective glucose biosensing at −0.100 V without any permselective membrane. The proposed sensor was challenged with different real samples without pretreatment showing an excellent correlation with the reported values.

Determination of butylparaben by adsorptive stripping voltammetry at glassy carbon electrodes modified with multi-wall carbon nanotubes

This work reports on the performance of glassy carbon electrodes (GCE) modified with a layer of multi-wall carbon nanotubes (MWCNTs) for the determination of butylparaben (BP) by adsorptive stripping voltammetry (AdSV). Several operating conditions and voltammetric parameters were examined. Under the chosen conditions, BP peak current obtained by differential pulse voltammetry increased linearly with BP concentration up to 100 μM with a limit of detection of 0.2 μM. A molecularly imprinted solid-phase extraction procedure (MISPE) was developed to improve the sensitivity and selectivity of BP electroanalysis when applied to real samples. The proposed methodology was successfully used for the quantification of BP in spiked water samples with recovery values between 82 and 85%. The MISPE procedure allowed the detection of BP at concentration levels of 0.02 μM in the presence of potential interfering substances such as 2,4,6-trichlorophenol (TPC), atrazine, paracetamol or diclofenac. • This work provides a sensitive and selective method to quantify butylparaben. • GCE modified with MWCNTs exhibited higher sensitivity for the AdSV analysis of BP. • A MISPE procedure improves the sensitivity and selectivity of BP electroanalysis. • The methodology proposed was successfully applied to river water samples.

Dispersion of bamboo type multi-wall carbon nanotubes in calf-thymus double stranded DNA

We report for the first time the use of double stranded calf-thymus DNA (dsDNA) to successfully disperse bamboo-like multi-walled carbon nanotubes (bCNT). The dispersion and the modified electrodes were studied by different spectroscopic, microscopic and electrochemical techniques. The drastic treatment for dispersing the bCNT (45min sonication in a 50% (v/v) ethanol:water solution), produces a partial denaturation and a decrease in the length of dsDNA that facilitates the dispersion of CNT and makes possible an efficient electron transfer of guanine residues to the electrode. A critical analysis of the influence of different experimental conditions on the efficiency of the dispersion and on the performance of glassy carbon electrodes (GCE) modified with bCNT–dsDNA dispersion is also reported. The electron transfer of redox probes and guanine residues was more efficient at GCE modified with bCNT dispersed in dsDNA than at GCE modified with hollow CNT (hCNT) dispersed in dsDNA, demonstrating the importance of the presence of bCNT.

Electrochemical determination of ascorbic acid and paracetamol in pharmaceutical formulations using a glassy carbon electrode modified with multi-wall carbon nanotubes dispersed in polyhistidine

Abstract This work reports on the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multi-wall carbon nanotubes (MWCNT) in polyhistidine (Polyhis) (GCE/MWCNT–Polyhis) for the simultaneous determination of ascorbic acid (AA) and paracetamol (PA). The modified electrode exhibited enhanced current responses and lower oxidation overvoltages, demonstrating excellent catalytic activities towards AA and PA oxidation compared to bare GCE. The linear dependence between the anodic peak currents and the square root of scan rates over the range of 0.005–0.300 V s−1 demonstrate that the electrooxidation of AA and PA occurs under diffusional control. The MWCNT–Polyhis modified GCE displayed a sensitivity of (3.8 ± 0.1) × 104 μA M−1 (r = 0.998) and a detection limit of 0.76 μM for the selective determination of AA in the presence of 1.00 × 10−4 M PA. Conversely, for the direct quantification of PA in the presence of 5.00 × 10−4 M AA, the sensitivity and the detection limit were (6.3 ± 0.2) × 105 μA M−1 (r = 0.997) and 32 nM, respectively. The proposed electrochemical sensor was successfully applied for quantifying AA and PA in commercial pharmaceutical formulations without any sample pretreatment.

Glassy carbon electrode coated with polyaniline-functionalized carbon nanotubes for detection of trace lead in acetate solution

The performance of glassy carbon electrodes (GCEs) coated with polyaniline-multiwalled carbon nanotube (MWCNT–CO–PANI) nanocomposite coatings was investigated in detection of Pb 2+ ions in a 0.1 M acetate buffer solution using square wave anodic stripping voltammetry (SWASV). It was found that the MWCNT–CO–PANI coated electrodes had a better performance than the bare GCEs. Different solvents were used to get a better dispersion of MWCNTs in the PANI matrix for higher stripping signals. The surface morphology and structure of the coated electrodes were examined using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and micro Raman spectroscopy, showing that the conductive PANI matrix worked as both a conductor to electrically connect the individual MWCNTs, and a binder to mechanically join the MWCNTs.

Surface manipulation for improving the sensitivity and selectivity of glassy carbon electrodes by electrochemical treatment

The performance of electrochemical sensor is related to the surface structure of electrode. Electrochemical treatment was often used to improve the performance of glassy carbon electrodes (GCEs) for the simplicity of operation. The densely compact oxide film formed on the surface of the electro-oxidized glassy carbon electrodes (GCEs-ox) could be changed to be porous by following electro-reduction of the GCEs-ox obtaining the totally reduced GCEs-ox (GCEs-re). The GCEs-re with a porous film exhibited high sensitivity in detecting epinephrine (EP) accompanying with poor stability and incapability of anti-interference from negatively charged ascorbic acid (AA) because both of AA and EP could permeate the porous film. Compared to the GCEs-re, the GCEs-ox with a densely compact film displayed relatively lower sensitivity but higher stability. To combine the advantages of both porous and densely compact oxide films, a partially reduced GCE-ox (GCE-ox-re) with an oxide film porous outer and densely compact inner was designed by controlling the electro-reduction time and potential, which will provide a new strategy for improving the performance of GCEs. The GCEs-ox-re exhibited high sensitivity, excellent stability and high selectivity in the detection of EP. In the presence of 0.1 mM AA, the anodic peak current of EP was directly proportional to its concentration in the range of 8.0 × 10 −9–2.0 × 10 −7 M and EP as low as 2.0 × 10 −9 M could be detected.

Glassy Carbon Electrodes Modified with Multiwall Carbon Nanotubes Dispersed in Polylysine

AbstractWe report the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multiwall carbon nanotubes (MWCNT) in polylysine (Plys) (GCE/MWCNT‐Plys). The resulting electrodes show an excellent electrocatalytic activity towards different bioanalytes like ascorbic acid, uric acid and hydrogen peroxide, with important decrease in their oxidation overvoltages. The dispersion of 1.0 mg/mL MWCNT in 1.0 mg/mL polylysine is highly stable, since after 2 weeks the sensitivity for hydrogen peroxide at GCE modified with this dispersion remained in a 90% of the original value. The MWCNT‐Plys layer immobilized on glassy carbon electrodes has been also used as a platform to build supramolecular architectures by self‐assembling of polyelectrolytes based on the polycationic nature of the polylysine used to disperse the nanotubes. The self‐assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing. The influence of glucose oxidase concentration and adsorption time as well as the effect of using polylysine or MWCNT‐Plys as polycationic layers for further adsorption of GOx is also evaluated.

Dispersion of multi-wall carbon nanotubes in polyethylenimine: A new alternative for preparing electrochemical sensors

In this work we report on the analytical performance of glassy carbon electrodes modified with a dispersion of multi-wall carbon nanotubes in polyethylenimine (GCE/(PEI/CNT)). The resulting electrodes show an excellent electrocatalytic activity toward different bioanalytes like ascorbic acid, dopamine, 3,4-dihydroxyphenylacetic acid (dopac) and hydrogen peroxide. An important decrease in the overvoltages for the oxidation of ascorbic acid (505 mV) and hydrogen peroxide (350 mV) and for the reduction of hydrogen peroxide (450 mV), as well as a dramatic improvement in the reversibility of the electrochemical behavior of dopamine and dopac is obtained. The currents are higher than those obtained with other dispersant agents like Nafion, concentrated acids or chitosan, evidencing the high efficiency of the dispersion in PEI. The GCE/(PEI/CNT) demonstrated to be highly reproducible, with 3.0% RSD for the sensitivity of hydrogen peroxide for 10 electrodes prepared with five different dispersions. Differences in sensitivity of 10.0% were obtained for hydrogen peroxide with electrodes prepared using the same dispersion even after 14 days preparation. The CNT/PEI layer immobilized on glassy carbon electrodes has been also used as a platform for building supramolecular architectures based on the self-assembling of polyelectrolytes without any pretreatment of the electrode surface, oxidation or derivatization of the carbon nanotubes, just taking advantages of the polycationic nature of the polymer used for dispersing the nanotubes. The self-assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing, with detection limits of 11 μM (0.02 g/L). Such an excellent performance of GCE/(PEI/CNT) toward hydrogen peroxide and the effectiveness of the use of CNT/PEI as a platform for obtaining supramolecular multistructures, represents a very good alternative for developing other enzymatic biosensors.

Demonstration of the advantages of using bamboo-like nanotubes for electrochemical biosensor applications compared with single walled carbon nanotubes

The modification of glassy carbon electrodes with random dispersions of nanotubes is currently the most popular approach to the preparation of carbon nanotube modified electrodes. The performance of glassy carbon electrodes modified with a random dispersion of bamboo type carbon nanotubes was compared with single walled carbon nanotubes modified glassy carbon electrodes and bare glassy carbon electrodes. The electrochemical performance of all three types for electrode were compared by investigating the electrochemistry with solution species and the oxidation of guanine and adenine bases of surface adsorbed DNA. The presence of edge planes of graphene at regular intervals along the walls of the bamboo nanotubes resulted in superior electrochemical performance relative to SWNT modified electrodes from two aspects. Firstly, with solution species the peak separation of the oxidation and reduction waves were smaller indicating more rapid rates of electron transfer. Secondly, a greater number of electroactive sites along the walls of the bamboo-carbon nanotubes (BCNTs) resulted in larger current signals and a broader dynamic range for the oxidation of DNA bases.

Studies of an Alkaline Activated Glassy Carbon Electrode on the Determination of Purines and DNA

Performance of glassy carbon electrode on the determination of purines and DNA was found to be improved dramatically by activating the GCE with a simple but effective electrochemical pretreatment. Characteristics such as lowering of oxidation potential, enhancement of peak current and elimination of fouling effect were found for the activated GCE. By flow injection analysis, good reproducibility with relative standard deviations of 0.59 and 2.01% (n = 11) and rather low detection limits of 0.6 + 0.1 and 3.0 ± 0.4 nM can be obtained for the analysis of guanine and adenine. Solutions of denatured calf thymus DNA were analyzed by differential pulse voltammetry with the activated GCE. Good agreement between the obtained results and the known values confirms the feasibility of the activated GCE for DNA analysis.