Voltammetric studies on the potent carcinogen, 7,12-dimethylbenz[a]anthracene: Adsorptive stripping voltammetric determination in bulk aqueous forms and human urine samples and detection of DNA interaction on pencil graphite electrode

7,12-Dimethylbenz[a]anthracene (DMBA), is a widely studied polycyclic aromatic hydrocarbon that has long been recognized as a very potent carcinogen. Initially, the electrochemical oxidation of DMBA at the glassy carbon and pencil graphite electrodes in non-aqueous media (dimethylsulphoxide with lithium perchlorate) was studied by cyclic voltammetry. DMBA was irreversibly oxidized in two steps at high positive potentials, resulting in the ill-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure on disposable pencil graphite electrode in aqueous solutions over the pH range of 3.0-9.0. The response was characterized with respect to pH of the supporting electrolyte, pre-concentration time and accumulation potential. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in acetate buffer, pH 4.8 at +1.15 V (vs. Ag/AgCl) (a pre-concentration step being carried out at a fixed potential of +0.60 V for 360 s). The process could be used to determine DMBA concentrations in the range 2-10 nM, with an extremely low detection limit of 0.194 nM (49.7 ng L⁻¹). The applicability to assay of spiked human urine samples was also illustrated. Finally, the interaction of DMBA with fish sperm double-stranded DNA based on decreasing of the oxidation signal of adenine base was studied electrochemically by using differential pulse voltammetry with a pencil graphite electrode at the surface and also in solution. The favorable signal-to-noise characteristics of biosensor resulted in low detection limit (ca. 46 nM) following a 300-s interaction. These results displayed that the electrochemical DNA-based biosensor could be used for the sensitive, rapid, simple and cost effective detection of DMBA-DNA interaction.     

Modification of carbon screen-printed electrodes by adsorption of chemically synthesized Bi nanoparticles for the voltammetric stripping detection of Zn(II), Cd(II) and Pb(II)

A simple procedure for the chemical synthesis of bismuth nanoparticles and subsequent adsorption on commercial screen-printed carbon electrodes offer reliable quantitation of trace zinc, cadmium and lead by anodic stripping square-wave voltammetry in nondeareated water samples. The influence of two hydrodynamic configurations (convective cell and flow cell) and the effect of various experimental variables upon the stripping signals at the bismuth-coated sensor are explored. The square-wave peak current signal is linear over the low ng mL⁻¹ range (120 s deposition), with detections limits ranging from 0.9 to 4.9 ng mL⁻¹ and good precision. Applicability to waste water certified reference material and drinking water samples is demonstrated. The attractive behaviour of the new disposable Bi nanoparticles modified carbon strip electrodes, coupled with the negligible toxicity of bismuth, hold great promise for decentralized heavy metal testing in environmental and industrial effluents waters.     

Adsorptive stripping square wave voltammetry (Ad-SSWV) accomplished with second-order multivariate calibration determination of fenitrothion and its metabolites in river water samples

A method, using stripping square wave voltammetry (Ad-SSWV), for the simultaneous determination of fenitrothion (FEN) and its metabolites: fenitrooxon (OXON) and 3-methyl-4-nitrophenol (3-MET) in environmental samples is reported. All three compounds produce, at mercury electrode (HMDE), an electrochemical signal due to an adsorptive-reductive process. The electrochemical approach shows a very high overlap degree for FEN and OXON voltammograms, however the adsorption kinetic profile could be used as an additional differential variable between both analytes. Second-order multivariate calibration has been tested to solve the mixture of the three compounds. The second-order assayed methods were parallel factor analysis (PARAFAC), unfolded partial least squares (U-PLS), multidimensional partial least squares (N-PLS) and the latest ones were used in combination with the residual bilinearization procedure RBL. U-PLS/RBL model was stated as the best second-order algorithm for the simultaneous determination of these three compounds up to 50 ng mL⁻¹ for each analyte. The detection limits and recovery values were 1.6 ng mL⁻¹ and 92 ± 7% for FEN; 3.7 ng mL⁻¹ and 101 ± 9% for OXON and 0.6 ng mL⁻¹ and 97 ± 8% for 3-MET.     

Double-ion imprinted polymer @magnetic nanoparticles modified screen printed carbon electrode for simultaneous analysis of cerium and gadolinium ions

A typical, reproducible, and rugged screen printed carbon electrode, modified with dual-ion imprinted beads, was fabricated employing the “surface grafting from” approach. For this, the acyl chloride functionalized magnetic nanoparticles were first immobilized and chemically attached with a typical functional monomer (but-2-enedioic acid bis-[(2-amino-ethyl)-amide]) on the electrode surface. This was subsequently subjected to the thermal polymerization in the presence of template ions (Ce(IV) and Gd(III)), cross-linker (ethylene glycol dimethacrylate), initiator (AIBN), and multiwalled carbon nanotubes. The modified sensor was used for the simultaneous analysis of both template ions in aqueous, blood serum, and waste-water samples, using differential pulse anodic stripping voltammetry which revealed two oxidation peaks for respective templates with resolution as much as 950 mV, without any cross reactivity, interferences and false-positives. The detection limits realized by the proposed sensor, under optimized conditions, were found to be as low as 0.07 ng mL⁻¹ for Ce(IV) and 0.19 ng mL⁻¹ for Gd(III) (S/N = 3) that could eventually be helpful for lanthanide estimation at stringent levels.     

Highly sensitive determination of mercury using copper enhancer by diamond electrode coupled with sequential injection–anodic stripping voltammetry

A highly sensitive determination of mercury in the presence of Cu(II) using a boron-doped diamond (BDD) thin film electrode coupled with sequential injection–anodic stripping voltammetry (SI–ASV) was proposed. The Cu(II) was simultaneously deposited with Hg(II) in a 0.5 M HCl supporting electrolyte by electrodeposition. In presence of an excess of Cu(II), the sensitivity for the determination of Hg(II) was remarkably enhanced. Cu(II) and Hg(II) were on-line deposited onto the BDD electrode surface at −1.0 V (vs. Ag/AgCl, 3 M KCl) for 150 s with a flow rate of 14 μL s⁻¹. An anodic stripping voltammogram was recorded from −0.4 V to 0.25 V using a frequency of 60 Hz, an amplitude of 50 mV, and a step potential of 10 mV at a stopped flow. Under the optimal conditions, well-defined peaks of Cu(II) and Hg(II) were found at −0.25 V and +0.05 V (vs. Ag/AgCl, 3 M KCl), respectively. The detection of Hg(II) showed two linear dynamic ranges (0.1–30.0 ng mL⁻¹ and 5.0–60.0 ng mL⁻¹). The limit of detection (S/N = 3) obtained from the experiment was found to be 0.04 ng mL⁻¹. The precision values for 10 replicate determinations were 1.1, 2.1 and 2.9% RSD for 0.5, 10 and 20 ng mL⁻¹, respectively. The proposed method has been successfully applied for the determination of Hg(II) in seawater, salmon, squid, cockle and seaweed samples. A comparison between the proposed method and an inductively coupled plasma optical emission spectrometry (ICP-OES) standard method was performed on the samples, and the concentrations obtained via both methods were in agreement with the certified values of Hg(II), according to the paired t-test at a 95% confidence level.     

Simultaneous voltammetric determination of morphine and noscapine by adsorptive differential pulse stripping method and least-squares support vector machines

An adsorptive differential pulse stripping method for the simultaneous determination of morphine and noscapine is proposed. The procedure involves an adsorptive accumulation of morphine and noscapine on a hanging mercury drop electrode (HMDE), followed by oxidation of adsorbed morphine and noscapine by voltammetric scan using differential pulse modulation. The optimum experimental conditions are: pH 10.0, accumulation potential of −100 mV versus Ag/AgCl, accumulation time of 150 s, scan rate of 40 mV s⁻¹ and pulse height of 100 mV. Morphine and noscapine peak currents were observed in same potential region at about +0.25 V. The simultaneous determination of morphine and noscapine by using voltammetry is a difficult problem in analytical chemistry, due to voltammogram interferences. The resolution of mixture of morphine and noscapine by the application of least-squares support vector machines (LS-SVM) was performed. The linear dynamic ranges were 0.01-3.10 and 0.015-2.75 μg mL⁻¹ and detection limits were 3 and 7 ng mL⁻¹ for morphine and noscapine, respectively. The capability of the method for the analysis of real samples was evaluated by the determination of morphine and noscapine in addict's human plasma with satisfactory results.     

Highly sensitive and selective fluorescence optosensor to detect and quantify benzo[a]pyrene in water samples

We describe here a method for detecting and quantifying the highly carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP) in water, based on a flow-trough optical sensor. The technique is fast (response time of 40 s) and simple and at the same time meets the standards of sensitivity and selectivity required by the European Guidelines on Water for Human Consumption. The optosensor is based on the on-line immobilization of BaP on a non-ionic resin (Amberlite XAD-4) solid support in a continuous-flow system. BaP was analyzed in a 15 mM H₂PO₄⁻/HPO₄²⁻ buffer solution with 25% (v/v) 1,4-dioxane at pH 7. Fluorescence intensity was measured at λ_ex/em=392/406 nm. The experimental conditions (reagent phase, pH, type and concentration of buffer solution and organic solvent) and flow-injection values (flow rate and injection volume) were carefully controlled. Under these conditions the optosensor was sensitive to a linear concentration range of between 3.0 and 250.0 ng l⁻¹ with a detection limit of 3.0 ng l⁻¹ and a standard deviation of 1.5% at 150 ng l⁻¹. The optosensor was applied to the quantification of BaP in drinking and waste water samples (95-105% recovery) in presence of the other 15 EPA PAHs at 1000 ng l⁻¹ concentration level. The influence of other fluorescent polycyclic aromatic hydrocarbons and potential interference from ions usually present in water was also evaluated.     

Electrochemical stripping voltammetry of gold ions for development of ultra-sensitive immunoassay for chlorsulfuron

The paper reports a highly sensitive enzyme free electrochemical immunoassay (EFEIA) for the detection of herbicide chlorsulfuron. The assay is based upon oxidative gold nanoparticle (GNP) dissolution in an acidic solution. The consequent release of large amounts of gold (Au) metal ions after dissolution of gold nanoparticles tagged to antibody leads to the development of sensitive stripping voltammetry based immunoassay. The detection is made possible by the reduction of Au^3 + ions at the screen printed electrode surface followed by metal analysis by using the square wave voltammetry technique. The sensitivity of chlorsulfuron detection by competitive assay procedure was 6.7 pg mL^− 1 for EFEIA in marked contrast to optical detection using Standard ELISA procedure that gives a sensitivity of 4.97 ng mL^− 1.     

Application of adsorptive stripping voltammetry to the simultaneous determination of bismuth and copper in the presence of nuclear fast red

A sensitive and selective method for the simultaneous determination of copper and bismuth by adsorptive stripping was developed using nuclear fast red (2-anthracenesulfonic acid, 4-amino-9,10-dihydro-1,3-dihydroxy-9,10-dioxo-, monosodium salt) as selective complexing agent onto hanging mercury drop electrode. In a single scan both metals gave peaks that were distinctly separated by 85 mV allowing their determination in the presence of each other. Optimal analytical conditions were found to be: nuclear fast red concentration of 80 μM, pH of 2.8 and adsorptive potential of −300 mV versus Ag/AgCl. With accumulation time of 180 s the peaks currents are proportional to concentration of copper and bismuth over the 1-100 and 5-60 ng mL⁻¹ range with detection limits of 0.2 and 1.2 ng mL⁻¹, respectively. The procedure was applied to simultaneous determination of copper and bismuth in some real samples.     

Electrochemical study of taxol (paclitaxel) by cathodic stripping voltammetry: determination in human urine

An analytical method for the determination of taxol (paclitaxel) via cathodic stripping square wave voltammetry has been developed. The method allows to achieve a detection limit of 5.2 ng ml⁻¹ and a determination limit of 11.0 ng ml⁻¹ working with a mercury drop electrode in 0.05 M boric acid/borate buffer pH 9.0, previously accumulated at −0.1 V (v.s. Ag/AgCl/KCl 3 M) for 360 s. Moreover, information about the mechanisms governing the reduction of taxol has been obtained from the studies of the instrumental parameters of square wave voltammetry technique. After addition of an internal standard, taxol was extracted from spiked human urine and the proposed method was successfully applied to the quantification of the analyte.     

An enzymeless organophosphate pesticide sensor using Au nanoparticle-decorated graphene hybrid nanosheet as solid-phase extraction

A sensitive enzymeless organophosphate pesticides (OPs) sensor is fabricated by using Au nanoparticles (AuNPs) decorated graphene nanosheets (GNs) modified glassy carbon electrode as solid phase extraction (SPE). Such a nanostructured composite film, combining the advantages of AuNPs with two dimensional GNs, dramatically facilitates the enrichment of nitroaromatic OPs onto the surface and realizes their stripping voltammetric detection of OPs by using methyl parathion (MP) as a model. The stripping voltammetric performances of captured MP were evaluated by cyclic voltammetric and square-wave voltammetric analysis. The combination of the nanoassembly of AuNPs-GNs, SPE, and stripping voltammetry provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs. The stripping analysis is highly linear over the MP concentration ranges of 0.001-0.1and 0.2-1.0 μg mL⁻¹ with a detection limit of 0.6 ng mL⁻¹. This designed enzymeless sensor exhibits good reproducibility and acceptable stability.     

Simultaneous determination of guanine and adenine in DNA using an electrochemically pretreated glassy carbon electrode

A simple and reliable method based on adsorptive stripping at an electrochemically pretreated glassy carbon electrode (GCE) was proposed for simultaneous or individual determination of guanine and adenine in DNA. The detection sensitivity of guanine and adenine was improved greatly by activating the GCE electrochemically. After accumulation on pretreated GCE at open circuit for 5 min or at the potential of +0.3 V for 120 s, guanine and adenine produced well-defined oxidation peaks at about +0.8 and +1.1 V, respectively in pH 5 phosphate buffer. The detection limit for individual measurement of guanine and adenine was 4.5 ng ml⁻¹ (3×10⁻⁸ mol l⁻¹) and 4 ng ml⁻¹ (3×10⁻⁸ mol l⁻¹), respectively. Acid-denatured DNA showed two oxidation peaks corresponding to guanine and adenine residues in the same buffer. The proposed method can be used to estimate the guanine and adenine contents in DNA with good selectivity in a linear range of 0.25-5 μg ml⁻¹.     

Determination of traces molybdenum by catalytic adsorptive stripping voltammetry

A reliable and very sensitive procedure for the determination of ultra trace of molybdenum is proposed. Molybdenum was determined by cathodic stripping differential pulse voltammetry based on the adsorption collection of the Mo(VI)-Tiron complex on a hanging mercury drop electrode (HMDE). The variation of peak current with pH, concentration of Tiron and chlorate, plus several instrumental parameters such as accumulation time, accumulation potential and scan rate, were optimized. Under optimized condition, the relationship between the peak current and molybdenum concentration is linear in the range of 0.010-21.0 ng ml⁻¹. The limit of detection was found to be 0.006 ng ml⁻¹. The relative standard deviation for 10 replicates determination of 0.6 and 10 ng ml⁻¹ Mo(VI) is equal to 1.3 and 0.9%, respectively. The method was applied to the determination of molybdenum in river water, tap water, well water, plant foodstuff samples such as cucumber, tomato, carrot, and certified steel reference materials.     

A disposable chronocoulometric sensor for heavy metal ions using a diaminoterthiophene-modified electrode doped with graphene oxide

The rapid simultaneous determination of cadmium, lead, copper, and mercury ions is performed by employing a disposable sensor modified with graphene oxide (GO) doped diaminoterthiophene (GO/DTT) for chronocoulometry (CC). The performances of CC with and without pre-deposition in two opposite potential step directions were compared with square wave anodic stripping voltammetry (SWASV) under various conditions. The surface of the GO/DTT modified screen print carbon electrode (SPCE) was characterized by SEM, EDXS, and electrochemical impedance spectroscopy (EIS). Experimental variables that affect the response signal such as the pH, deposition time, type of supporting electrolyte, concentration of DTT, content ratio of GO to DTT, and Nafion content were optimized. Interference effects due to other heavy metal ions were also investigated. The dynamic ranges of SWASV and CC were between 1 ng mL⁻¹ and 2.5 μg mL⁻¹ and between 1 ng mL⁻¹ and 10 μg mL⁻¹, respectively. The detection limits for Cd²⁺, Pb²⁺, Cu²⁺, Hg²⁺ ions were 1.9 ± 0.4 ng mL⁻¹, 2.8 ± 0.6 ng mL⁻¹, 0.8 ± 0.2 ng mL⁻¹, and 2.6 ± 0.9 ng mL⁻¹ for the CC stripping method; 2.6 ± 0.2 ng mL⁻¹, 0.5 ± 0.1 ng mL⁻¹, 1.8 ± 0.3 ng mL⁻¹, and 3.2 ± 0.3 ng mL⁻¹ for the CC deposition method; and 7.1 ± 0.9, 1.9 ± 0.3, 0.4 ± 0.1, and 0.7 ± 0.1 ng mL⁻¹ for SWASV. The reliability of the method for point-of-analysis was evaluated by analyzing a urine standard reference material and some water samples.     

Perfluorinated anion-exchange polymer mercury film electrode for anodic stripping voltammetric determination of zinc(II): effect of model organic compounds

The determination of zinc ion (1-60 ng ml⁻¹) by anodic square-wave stripping voltammetry on an anion-exchange perfluorinated polymer Tosflex mercury film electrodes (TMFE) was evaluated. The detection limit was 0.1 ng ml⁻¹ Zn(II). The effect of various organic compounds (gelatin, albumin, starch, camphor, humic acid, Triton X-100, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)) is explored. The results indicate that due to the size-exclusion and ion-exchange properties of Tosflex film, the TMFE is considerably more resistant to organic interference than the bare mercury film electrode.     

An electrochemical immunosensor based on enzyme-encapsulated liposomes and biocatalytic metal deposition

A novel electrochemical immunosensor based on double signal amplification of enzyme-encapsulated liposomes and biocatalytic metal deposition was developed for the detection of human prostate specific antigen (PSA). Alkaline phosphatase (ALP)-encapsulated and detection antibody-functionalized liposomes were first prepared and used as the detection reagent. In the sandwich immunoassay, the model analyte PSA was first captured by anti-PSA capture antibody immobilized on the electrode and then sandwiched with the functionalized liposomes. The bound liposomes were then lysed with surfactant to release the encapsulated ALP, which served as secondary signal amplification means. ALP on the electrode surface initiated the hydrolysis of ascorbic acid 2-phosphate (AA-p) to produce ascorbic acid. The latter, in turn, reduced silver ions on the electrode surface, leading to deposition of the metal silver on the electrode surface. Linear sweep voltammetry (LSV) was chosen to detect the amount of the deposited silver. The results showed that the anodic stripping peak current was linearly dependent on the PSA concentration in the range of 0.01-100 ng mL⁻¹, and a detection limit as low as 0.007 ng mL⁻¹ can be obtained. Since the cut-off value of human PSA is 4 ng mL⁻¹, the proposed electrochemical immunosensor would be expected to gain widespread applications for the detection of PSA in clinical diagnosis.     

Simultaneous determination of nickel(II) and cobalt(II) by square wave adsorptive stripping voltammetry on a rotating-disc bismuth-film electrode

This works reports the use of square-wave adsorptive stripping voltammetry (SWAdSV) for the simultaneous determination of Ni(II) and Co(II) on a rotating-disc bismuth-film electrode (BFE). The metal ions in the non-deoxygenated sample were complexed with dimethylglyoxime (DMG) and the complexes were accumulated by adsorption on the surface of the BFE. The stripping step was carried out by using a square-wave potential-time voltammetric excitation signal. Electrochemical cleaning of the bismuth film was employed, enabling the same bismuth film to be used for a series of measurements. The experimental variables (choice of the working electrode substrate, the presence of oxygen, the DMG concentration, the buffer concentration, the preconcentration potential, the accumulation time, the rotation speed and the SW parameters) as well as potential interferences were investigated and the figures of merit of the methods were established. Using the selected conditions, the 3σ limits of detection were 70 ng l⁻¹ for Co(II) and 100 ng l⁻¹ for Ni(II) (for 300 s of preconcentration) and the relative standard deviations were 2.3% for Co(II) and 3.9% for Ni(II) at the 2 μg l⁻¹ level (n = 8). Finally, the method was applied to the determination of nickel and cobalt in real samples with satisfactory results.     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between tetracarboxy aluminum phthalocyanine and tetra-N-hexadecylpyridiniumyl porphyrin

A new method was developed for determination of micro amounts of nucleic acids based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic tetracarboxy aluminum phthalocyanine (AlC₄Pc) and a cationic tetra-N-hexadecylpyridiniumyl porphyrin (TC₁₆PyP). The fluorescence of the AlC₄Pc, with the maximum emission wavelength at 701 nm, could be quenched by TC₁₆PyP at its proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence is proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 1-200 ng mL⁻¹ for fish sperm DNA (FS DNA) and 2-400 ng mL⁻¹ for calf thymus DNA (CT DNA). The corresponding detection limits are 0.59 ng mL⁻¹ for FS DNA and 0.82 ng mL⁻¹ for CT DNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.     

A new high-performance liquid chromatography assay for the determination of sesquiterpene lactone 15-deoxygoyazensolide in rat plasma

A simple, rapid and sensitive high-performance liquid chromatography method was developed for the analysis of the sesquiterpene lactone 15-deoxygoyazensolide (LAC15-D) in rat plasma samples. The chromatographic separation was achieved on a LiChrospher^® RP18 column using methanol:water (50:50, v/v) containing 0.6% acetic acid as mobile phase, at a flow rate of 0.7 mL min⁻¹. UV detection was carried out at 270 nm. Phenytoin was used as internal standard. Prior to the analysis, the rat plasma samples were submitted to liquid-liquid extraction with dichloromethane. The mean absolute recoveries were 73% with R.S.D. values lower than 3.5. The method was linear over the 6.0-2000 ng mL⁻¹ concentration range and the quantification limit was 6.0 ng mL⁻¹. Within-day and between-day assay precision and accuracy were studied at three concentration levels (15, 300 and 480 ng mL⁻¹) and were lower than 15%. The validated method was used to measure the plasmatic concentration of LAC15-D in rats that received a single intraperitoneal dose of 30 mg kg⁻¹.     

Production and characterization of a broad-specificity polyclonal antibody for O,O-diethyl organophosphorus pesticides and a quantitative structure-activity relationship study of antibody recognition

Polyclonal antibody (PAb) with broad-specificity for O,O-diethyl organophosphorus pesticides (OPs) against a generic hapten, 4-(diethoxyphosphorothioyloxy)benzoic acid, was produced. The obtained PAb showed high sensitivity to seven commonly used O,O-diethyl OPs in a competitive indirect enzyme-linked immunosorbent assay (ciELISA) using a heterologous coating antigen, 4-(3-(diethoxyphosphorothioyloxy)phenylamino)-4-oxobutanoic acid. The 50% inhibition value (IC₅₀) was 348 ng mL⁻¹ for parathion, 13 ng mL⁻¹ for coumaphos, 22 ng mL⁻¹ for quinalphos, 35 ng mL⁻¹ for triazophos, 751 ng mL⁻¹ for phorate, 850 ng mL⁻¹ for dichlofenthion, and 1301 ng mL⁻¹ for phoxim. The limit of detection (LOD) met the ideal detection criteria of all the seven OP residues. A quantitative structure-activity relationship (QSAR) model was constructed to study the mechanism of antibody recognition using multiple linear regression analysis. The results indicated that the frontier-orbital energies (energy of the highest occupied molecular orbital, E_HOMO, and energy of the lowest unoccupied molecular orbital, E_LUMO) and hydrophobicity (log of the octanol/water partition coefficient, log P) were mainly responsible for the antibody recognition. The linear equation was log(IC₅₀) = −63.274E_HOMO + 15.985E_LUMO + 0.556 log P − 25.015, with a determination coefficient (r²) of 0.908.