Voltammetric determination of organic nitrogen compounds in environmental samples using carbon paste electrode modified with activated carbon (original) (raw)
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Talanta, 2007
The presence of trace neutral organonitrogen compounds as carbazole and indole in derivative petroleum fuels plays an important role in the car's engine maintenance. In addition, these substances contribute to the environmental contamination and their control is necessary because most of them are potentially carcinogenic and mutagenic. For those reasons, a reliable and sensitive method was proposed for the determination of neutral nitrogen compounds in fuel samples, such as gasoline and diesel using preconcentration with modified silica gel (Merck 70-230 mesh ASTM) followed by differential pulse voltammetry (DPV) technique on a glassy carbon electrode. The electrochemical behavior of carbazole and indole studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF 4 0.1 mol L −1 ) for indole (−2.27 V) and carbazole (−2.67 V) versus Ag|AgCl|KCl sat reference electrode. The proposed DPV method showed a good linear response range from 0.10 to 300 mg L −1 and a limit of detection (L.O.D) of 7.48 and 2.66 g L −1 for indole and carbazole, respectively. The results showed that simultaneous determination of indole and carbazole presents in spiked gasoline samples were 15.8 ± 0.3 and 64.6 ± 0.9 mg L −1 and in spiked diesel samples were 9.29 ± 1 and 142 ± 1 mg L −1 , respectively. The recovery was evaluated and the results shown the values of 88.9 ± 0.4 and 90.2 ± 0.8% for carbazole and indole in fuel determinations. The proposed method was also compared with UV-vis spectrophotometric measures and the results obtained for the two methods were in good agreement according to the F and t Student's tests.
Dyes and Pigments, 2007
This work presents an electroanalytical method based on square-wave voltammetry (SWV) for the determination of quinizarine (QNZ) in a mixture of BrittoneRobinson buffer 0.08 mol L ÿ1 with 30% of acetonitrile. The QNZ was oxidized at glassy carbon electrode in and the well-defined peak at þ0.45 V vs. Ag/AgCl can be used for its determination as colour marker in fuel samples. All parameters were optimized and analytical curves can be constructed for QNZ concentrations ranging from 2.0 Â 10 ÿ6 mol L ÿ1 to 1.4 Â 10 ÿ5 mol L ÿ1 , using f ¼ 60 Hz and E sw ¼ 25 mV. The method offers a limit detection of 4.12 Â 10 ÿ7 mol L ÿ1 and a standard deviation of 4.5% when six measurements of 1.25 Â 10 ÿ5 mol L ÿ1 are compared. The method was successfully applied for determining QNZ in gasoline and diesel oil and the obtained results showed good agreement with those reported previously.
Determination of aniline and quinoline compounds in textiles
Journal of chromatography. A, 2016
A simple method for simultaneous determination of twenty-one analytes, belonging to two classes of compounds, aromatic amines and quinolines, is presented. Several of the analytes considered in this study frequently occur in textiles goods on the open market and have been related to allergic contact dermatitis and/or are proven or suspected carcinogens. The method includes an efficient clean-up step using graphitized carbon black (GCB) that simplifies and improves the robustness of the subsequent GC-MS analysis. Briefly, after solvent extraction of the textile sample, the extract is passed through a GCB SPE cartridge that selectively retain dyes and other interfering compounds present in the matrix, producing a clean extract, suitable for GC-MS analysis, is obtained. The method was evaluated by spiking blank textiles with the selected analytes. Method quantification limits (MQL) ranged from 5 to 720ng/g depending on the analyte. The linear range of the calibration curves ranged over...
The Scientific World Journal, 2012
Genotoxic nitrated polycyclic aromatic hydrocarbons (NPAHs) are formed during incomplete combustion processes by reaction of polycyclic aromatic hydrocarbons (PAHs) with atmospheric nitrogen oxides. 1-Nitropyrene, 2-nitrofluorene, and 3-nitrofluoranthene as the dominating substances are used as markers of NPAHs formation by these processes. In the presented study, voltammetric properties and quantification of these compounds and of 5-nitroquinoline (as a representative of environmentally important genotoxic heterocyclic compounds) have been investigated using a mercury meniscus modified silver solid amalgam electrode (m-AgSAE), which represent a nontoxic alternative to traditional mercury electrodes. Linear calibration curves over three orders of magnitude and limits of determination mostly in the 10 −7 mol L −1 concentration range were obtained using direct current and differential pulse voltammetry. Further, satisfactory HPLC separation of studied analytes in fifteen minutes was achieved using 0.01 mol L −1 phosphate buffer, pH 7.0 : methanol (15 : 85, v/v) mobile phase, and C 18 reversed stationary phase. Limits of detection of around 1 · 10 −5 mol L −1 were achieved using amperometric detection at m-AgSAE in wall-jet arrangement for all studied analytes. Practical applicability of this technique was demonstrated on the determination of 1-nitropyrene, 2-nitrofluorene, 3-nitrofluoranthene, and 5-nitroquinoline in drinking water after their preliminary separation and preconcentration using solid phase extraction with the limits of detection around 1 · 10 −6 mol L −1 .
Analytical Sciences, 1993
Coenzyme pyrroloquinoline quinone (PQQ) was electrochemically detected with high sensitivity and high selectivity by employing its redox catalytic function in reversed-phase high-performance liquid chromatography. This catalytic reaction involves oxidative decarboxylation of glycine by PQQ and the reoxidation of the reduced PQQ by Fe(CN)63_ to accumulate Fe(CN)64-, of which the electrochemical detection allows amplified detection of PQQ. Increase by two orders of magnitude of the current was achieved as compared with a direct reductive detection, at a reaction time of 3 min and a reaction temperature of 25° C. The detection limit was 0.2 pmol (10.8 M, 20 µl). The present method was applied to quantification of PQQ in table vinegar, milk, and swine serum.
Electrochemical detection of 4-nitrophenol based on biomass derived activated carbons
A novel method for detecting an environmental pollutant, 4-nitrophenol (4-NP), by exploiting biomass-derived activated carbon (AC) is reported. The electrochemical performances of the 4-NP sensor were assessed by cyclic and linear sweep voltammetries. The presence of oxygen surface functional groups and heteroatoms (72.6% C, 6.1% H, 6.5% N, and 7.5% S) in the biomass-derived AC with high surface area (1555 m2 g1) are found to be responsible for the excellent catalytic activities and reversible redox behaviors observed during the detection of 4-NP. The effects of pH of the electrolyte buffer solution, accumulated potential and duration as well as the analyte concentration on the electrocatalytic performance of the sensor were investigated. Consequently, a linear correlation between the cathodic reduction peak current with 4-NP concentration up to 500 mM with a detection limit and sensitivity of 0.16 mM and 5.810 mA mM1 cm2, respectively, were observed over the AC-modified GCE in 0.05 M acetate buffer solution (pH 5.0), surpassing the existing modified electrodes in the literature. The facile 4-NP sensor thus implemented is also advantageous for its simplicity, stability, reliability, durability, and low cost, rendering practical applications for real sample systems
Electroanalysis, 2010
A detailed study of the electrochemical oxidation of Benzo[a]pyrene (BaP) at the glassy carbon and pencil graphite electrodes was carried out in aqueous and nonaqueous media. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response at pencil graphite electrode in acetate buffer, pH 4.8 at þ 1.13 V (vs. Ag/ AgCl) (a preconcentration step being carried out at a fixed potential of þ 0.70 V for 180 s). The process could be used to determine BaP concentrations in the range 0.25-1.25 mM, with a detection limit of 0.027 mM (6.82 mg L À1). The applicability to assay of spiked human urine samples was also illustrated.
Journal of Solid State Electrochemistry, 2009
A p-duroquinone (tetramethyl-p-benzoquinone) modified carbon paste electrode (DMCPE) was employed to study the electrocatalytic reduction of nitrite in aqueous solutions using cyclic voltammetry (CV), double potentialstep chronoamperometry, and differential pulse voltammetry (DPV). It has found that under an optimum condition (pH 1.00), the reduction of nitrite at the surface of DMCPE occurs at a potential of about 660 mV less negative than that of an unmodified carbon paste electrode (CPE). The catalytic rate constant, k′ h , based on Andrieux and Saveant theoretical model was calculated as k' h ¼ 4:56 Â 10 À5 cm s À1 for scan rate 10 mV s -1 . Also, the apparent diffusion coefficient, D app , was found as 2.5×10 -10 and 3.61×10 -5 cm 2 s -1 for pduroquinone in carbon paste matrix and nitrite in aqueous buffered solution, respectively. The values for αn α were estimated to be −0.65 and −0.19 for the reduction of nitrite at the surface of DMCPE and CPE, respectively. The electrocatalytic reduction peak currents showed a linear dependence on the nitrite concentration, and a linear analytical curve was obtained in the ranges of 5.0×10 -5 M to 8.0×10 -3 M and 6.0×10 -6 M to 8.0×10 -4 M of nitrite concentration with CV and DPV methods, respectively. The detection limits (2σ) were determined as 2.5×10 -5 M and 4.3×10 -6 M by CV and DPV methods. This method was also applied as a simple, selective and precise method for determination of nitrite in real samples (the weak liquor from the wood and paper factory of Mazandaran province in Iran) by using a standard addition method.
Journal of Electroanalytical Chemistry, 2001
The reduction peak of quinone in aprotic media appears at a positively shifted potential in the presence of acids, which play a role as proton sources. Since the height of the newly developed peak shows a good correlation with the concentration of the acid, it can be utilized to determine the concentration of weak acids. Although the magnitude of the peak potential shift (DE p) decreases as the water content in the solution increases, the presence of a Brønsted acid still leads to a significantly large DE p in an acetonitrile +water mixture (9/1, v/v) when a proper quinone derivative is chosen. DE p depends on not only the acidity of proton sources but also the basicity in quinone derivatives. Among the various quinones examined in the present study, tetramethyl-1,4-benzoquinone (duroquinone) exhibits the largest DE p and is found to be a suitable redox-active additive for the selective analysis of a variety of organic acids. Based on these results, conventional voltammetric techniques, e.g. differential pulse voltammetry, square-wave voltammetry and linear sweep voltammetry, can be employed to determine various biologically important acids with protonated amine or carboxylate groups. The quantitative analyses of histamine, maleic acid and pyruvic acid are successfully demonstrated in the 10 − 5 M range with a high sensitivity of 17 19 mA mM − 1 by linear sweep voltammetry.
Talanta, 2010
A new and sensitive electroanalytical method for simultaneous determination of selected drugs, 4-aminophenazone (4-AP) and caffeine (CAF) has been developed and validated. Cyclic voltammetry (CV) was used to study the electrochemical behavior of the drugs, while differential pulse voltammetry (DPV) was used to determine 4-AP and CAF simultaneously. A pre-treated graphite pencil electrode (PTGPE) was used as the working electrode, a Ag/AgCl (3.0 M KCl) electrode served as the reference electrode, and a platinum wire as the auxiliary electrode. Determination of drugs was performed in phosphate buffer solution (PBS) of pH ¼ 3.0. The separation of the oxidation peak potentials for 4-AP-CAF was found to be 0.930 V. This difference was large enough to determine 4-AP and CAF individually and simultaneously. The dependence of the current on pH, concentration and scan rate was investigated to optimize the experimental conditions for simultaneous determination. The calibration plots for both the drugs were linear in certain concentration ranges. The linearity range for 4-AP was 1 mM to 11 mM and for CAF 1 mM to 9 mM, the concentration of each drug was varied by keeping the other constant, and achieved lower detection limit of 7.96 Â 10 À8 M for 4-AP and 9.81 Â 10 À9 M for CAF. The developed method was found to be precise, selective and rapid for the simultaneous determination of 4-AP and CAF. The proposed method has been applied for the determination of 4-AP and CAF in real samples.