Chromium(III) determination without sample treatment by batch and flow injection potentiometry

A new and easy device for direct detection of chromium(III) in batch and flow analysis without previous oxidation/reduction or preconcentration steps of samples is designed and evaluated. For this purpose a potentiometric sensor with solid state membrane based on carbon paste matrix is developed. The sensor is modified with di(2-hydroxyphenylimino)ethane and the principal analytical parameters of the potentiometric response in batch and flow analysis are optimized and calculated. Optimal detection limits (1.4 × 10⁻⁷ M in static mode and 5.4 × 10⁻⁷ M in on-line analysis) and selectivity to trivalent chromium are obtained in both analysis modes. The use of this device to direct detection of chromium(III) in real samples is tested using a sediment Certified Reference Material. Chromium(III) determination is also carried out with successful results in environmental samples such as extracts from soils used as barriers in landfills and industrial samples such as waste waters from electroplating industries.     

Comparative studies of mercapto thiadiazoles self-assembled on gold nanoparticle as ionophores for Cu(II) carbon paste sensors

Comparative studies of the potentiometric behavior of three mercapto compounds [2-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)phenol] (MTMP), [5-(2-methoxy benzylidene amino)-1,3,4-thiadiazole-2-thiol] (MBYT) and [5-(pyridin-2-ylmethyleneamino)-1,3,4-thiadiazole-2-thiol] (PYTT) self-assembled on gold nanoparticles (GNPs) as ionophores in carbon paste electrodes (CPEs) have been made. These mercapto thiadiazole compounds were self-assembled onto gold nanoparticles and then incorporated within carbon paste electrode. The self-assembled ionophores exhibit a high selectivity for copper ion (Cu²⁺), in which the sulfur and nitrogen atoms in their structure play a role as the effective coordination donor site for the copper ion. These carbon paste electrodes were applied as indicator electrodes for potentiometric determination of copper ions. The sensor based on PYTT exhibits the working concentration range of 4.0 × 10⁻⁹ to 7.0 × 10⁻² M and a Nernstian slope of 28.7 ± 0.3 mV decade⁻¹ of copper activity. The detection limit of electrode was 1.0 × 10⁻⁹ M and potential response was pH independent across the range of 3.0-6.5. It exhibited a quick response time of <5 s and could be used for a period of 45 days. The ion selectivity of this electrode for Cu²⁺ was over 10⁴ times that for other metal cations. The application of prepared sensors has been demonstrated for the determination of copper ions in spiked water and natural water samples.     

Carbon paste electrode modified with silver thimerosal for the potentiometric flow injection analysis of silver(I)

The utility of carbon paste electrode modified with silver ethylmercurythiosalicylate (silver thimerosal) in both static mode and flow injection analysis (FIA) is demonstrated. The electrode was fully characterized in terms of composition, response time, thermal stability, usable pH and ionic strength ranges. It has been shown that diisononyl phthalate (DINP) acts as more suitable solvent mediator for preparation of the electrode, which exhibits linear response range to Ag(I) extending from 5.0 × 10⁻⁷ to 1.0 × 10⁻³ M with detection limit of 2.5 × 10⁻⁷ M and Nernstian slope of 59.3 ± 1.0 mV/decade. The proposed chemically modified carbon paste electrode shows a very good selectivity for Ag(I) over a wide variety of metal ions and successfully used for the determination of the silver content of silver sulphadiazine (burning cream) and developed radiological films. The electrode was also used as an indicator electrode in the potentiometric titration of thiopental and thimerosal with AgNO₃.     

Development of an enzymeless biosensor for the determination of phenolic compounds

The construction of amperometric enzymeless biosensors for phenolic compounds determination, using carbon paste electrode modified with copper phtalocyanine (CuPc) and histidine (His), based on the chemistry of the dopamine β-monooxygenase (DβM) enzyme that catalyzes the hydroxylation of the dopamine and its analogs is shown. The modified carbon paste was evaluated on electrodes constructed in two ways: putting the paste into a cavity of a rotating disk electrode and a platinum slide electrode fixed into a glass tube. The sensor in hydrodynamic conditions presented a linear response range between 30 and 250 μmol l⁻¹, with a sensitivity of 4.6±0.1 nA l μmol⁻¹ cm⁻² for catechol, response time of 3 s and lifetime of about 50 days when stored at room temperature. The sensor in static conditions showed a linear response range from 40 to 250 μmol l⁻¹, with a sensitivity of 0.30±0.01 nA l μmol⁻¹ cm⁻² for catechol. The sensors presented the following relative response order for dopamine and some analog species: catechol>dopamine>guaiacol>serotonin>phenol.     

Determination of l-histidine by modified carbon paste electrode using tetra-3,4-pyridinoporphirazinatocopper(II)

This paper describes a potentiometric method for determination of l-histidine (l-his) in aqueous media, using a carbon paste electrode modified with tetra-3,4-pyridinoporphirazinatocopper(II) (Cu (3,4tppa)). The electrode exhibits linear response to the logarithm of the concentration of l-histidine from 2.4 × 10⁻⁵ to 1.0 × 10⁻² M, with a response slope of −49.5 ± 1 mV and response time of about 1.5 min. The detection limit according to IUPAC recommendation was 2.0 × 10⁻⁵ M. The proposed electrode shows a good selectivity for l-his over a wide variety of anions. This chemically modified carbon paste electrode was successfully used for the determination of l-his in a synthetic serum and RANDOX control serum solutions.     

Cobalt phthalocyanine as a novel molecular recognition reagent for batch and flow injection potentiometric and spectrophotometric determination of anionic surfactants

Cobalt(II) phthalocyanine [Co(II)Pc] is used as both an ionophore and chromogen for batch and flow injection potentiometric and spectrophotometric determination of anionic surfactants (SDS), respectively. The potentiometric technique involves preparation of a polymeric membrane sensor by dispersing [Co(II)Pc] in a plasticized PVC membrane. Under batch mode of operation, the sensor displays a near-Nernstian slope of −56.5 mV decade⁻¹, wide response linear range of 7.8 × 10⁻⁴ to 8.0 × 10⁻⁷ mol L⁻¹, lower detection limit of 2.5 × 10⁻⁷ mol L⁻¹ and exhibits high selectivity for anionic surfactants in the presence of many common ions. Under hydrodynamic mode of operation (FIA), the slope of the calibration plot, limit of detection, and working linear range are −51.1 mV decade⁻¹, 5.6 × 10⁻⁷ and 1.0 × 10⁻³ to 1.0 × 10⁻⁶ mol L⁻¹, respectively. The spectrophotometric method is based on the use of [Co(II)Pc] solution in dimethylsulfoxide (DMSO) as a chromogenic reagent. The maximum absorption of the reagent at 658 nm linearly decreases with the increase of anionic surfactant over the concentration range 2-30 μg mL⁻¹. The lower limit of detection is 1 μg mL⁻¹ and high concentrations of many interfering ions are tolerated. Flow injection spectrophotometric measurements are carried out by injection of the surfactant test solution in a stream of the reagent in DMSO. The sample throughput, working range and lower detection limit are 25-30 samples h⁻¹, 4-60 and 2 μg mL⁻¹, respectively. The potentiometric and spectrophotometric techniques are applied to the batch and flow injection measurements of anionic surfactants in some commercial detergent products. The results agree fairly well with data obtained using the standard methylene blue spectrophotometric method.     

Solid-contact potentiometric sensor for ascorbic acid based on cobalt phthalocyanine nanoparticles as ionophore

A novel solid-contact potentiometric sensor for ascorbic acid based on cobalt phthalocyanine nanoparticles (NanoCoPc) as ionophore was fabricated without any need of auxiliary materials (such as membrane matrix, plasticizer, and other additives). The electrode was prepared by simple drop-coating NanoCoPc colloid on the surface of a glassy carbon electrode. A smooth, bright and blue thin film was strongly attached on the surface of the glassy carbon electrode. The electrode showed high selectivity for ascorbic acid, as compared with many common anions. The influences of the amount of NanoCoPc at the electrode surface and pH on the response characteristics of the electrode were investigated. To overcome the instability of the formal potential of the coated wire electrode, a novel electrochemical pretreatment method was proposed for the potentiometric sensor based on redox mechanism. This resulting sensor demonstrates potentiometric response over a wide linear range of ascorbic acid concentration (5.5 × 10⁻⁷ to 5.5 × 10⁻² M) with a fast response (<15 s), lower detection limit (ca. 1.0 × 10⁻⁷ M), and a long-term stability. Furthermore, microsensors based on different conductors (carbon fiber and Cu wire) were also successfully fabricated for the determination of practical samples.     

Use of organofunctionalized nanoporous silica gel to improve the lifetime of carbon paste electrode for determination of copper(II) ions

A new functionalized nanoporous silica gel with dipyridyl group (DPNSG) was synthesized. Then, the potentiometric response of the copper(II) ion was investigated at a carbon paste electrode chemically modified with this newly designed functionalized nanoporous silica gel. The electrodes with DPNSG proportions of 15.0% (w/w) demonstrated very stable potentials. Calibration plots with Nernstian slopes for Cu²⁺ were observed, 28.4 (±1.0) mV decade⁻¹, over a wide linear concentration range (1.0 × 10⁻⁷ to 1.0 × 10⁻² M). The electrode exhibited a detection limit of 8.0 × 10⁻⁸ M. Moreover, the selectivity coefficients measured by the match potential method in acetate buffer, pH 5.5, were investigated. The electrode presented a response time of ∼50 s, high performance, high sensitivity in a wide range of cation activities and good long-term stability (more than 9 months). The method was satisfactory and was used to determine the copper ion concentration in waste waters, contaminated by this metal.     

Ag selective electrode based on glassy carbon electrode covered with polyaniline and thiacalix[4]arene as neutral carrier

Potentiometric sensor based on glassy carbon electrode covered with polyaniline and neutral carrier, e.g. thiacalix[4]arene containing pyridine fragments in the substituents in the lower rim has been developed and applied for determination of Ag⁺ ions in the range from 1.0 × 10⁻² to 5.0 × 10⁻⁷ M with the response time of 12 s. The presence of thiacalixarene in the surface layer improves the reversibility and selectivity of the signal towards transient metal ions. The potentiometric selectivity coefficients were determined for various measurement conditions. As shown, the pH control and the use of NaF as a masking agent fully eliminate the interfering effect of Hg²⁺ and Fe³⁺ ions, respectively. The reaction of Ag⁺ with thiacalixarene was proved by the investigation of the extraction of picrate complexes of transient metals in the organic phase. The potentiometric sensor developed was successfully used for the potentiometric determination of silver sulfathiazole (Argosulfan™).     

A highly selective fluorescent sensor for Cu based on 2-(2′-hydroxyphenyl)benzoxazole in a poly(vinyl chloride) matrix

This paper describes a copper selective optical chemical sensor based on static quenching of the fluorescence of 2-(2′-hydroxyphenyl)benzoxazole entrapped in a poly(vinyl chloride) (PVC) membrane. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensors exhibit stable response over the concentration range from 4.0 × 10⁻⁸ M to 5.0 × 10⁻⁵ M Cu²⁺ at pH 4.0-6.5, and a high selectivity. The response time for Cu²⁺ with concentration ≤5 × 10⁻⁶ M is less than 7 min. The optode can be regenerated using 0.1 M HCl and acetate buffer solution. The sensor has been used for direct measurement of copper content in river water samples with a relative error less than 4% with reference to that obtained by atomic absorption spectrometry.     

Copper(II)-selective electrode based on dithioacetal

A PVC membrane electrode for copper ion based on 1,3-dithiane,2-(4-methoxy phenyl) as ionophore and o-nitrophenyl octyl ether as a plasticizer is demonstrated. The electrode exhibits a Nernstian slope of 29.5±1 mV per decade in a linear range of 3.0×10⁻⁶ to 5.0×10⁻² M for Cu²⁺ ion. The detection limit of this electrode is 1.0×10⁻⁶ mol/l. This sensor has a very short response time of about 5 s and could be used in a pH range of 4.0-7.0. High selectivity was obtained over a wide variety of metal ions. The proposed electrode was successfully applied as an indicator electrode for the potentiometric titration of copper ion with EDTA and for the direct determination of copper in river water.     

Potentiometric stripping analysis of methyl and ethyl parathion employing carbon nanoparticles and halloysite nanoclay modified carbon paste electrode

Carbon nanoparticles (CNPs) and halloysite nanoclay (HNC) modified carbon paste electrode (HNC–CNP–CPE) was developed for the determination of methyl parathion (MP) and ethyl parathion (EP). The electrochemical behavior of these molecules was investigated employing cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS) and potentiometric stripping analysis (PSA). After optimization of analytical conditions employing this electrode at pH 5.0 in acetate buffer (0.1 M), the peak currents were found to vary linearly with its concentration in the range of 1.55 × 10⁻⁹ to 3.67 × 10⁻⁶ M and 1.21 × 10⁻⁹ to 4.92 × 10⁻⁶ M for MP and EP, respectively. The detection limits (S/N = 3) of 4.70 × 10⁻¹⁰ M and 3.67 × 10⁻¹⁰ M were obtained for MP and EP, respectively, using PSA. The prepared modified electrode showed several advantages such as simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. The proposed method was employed for the determination of MP and EP in fruits, vegetables, water and soil samples.     

Construction and performance characterization of ion-selective electrodes for potentiometric determination of phenylpropanolamine hydrochloride applying batch and flow injection analysis techniques

New phenylpropanolamine hydrochloride (PPA.Cl)-selective electrodes of the conventional polymer membrane type, based on incorporation of phenylpropanolamine-tetraphenylborate (PPA-TPB) ion-pair or phenylpropanolamine-phosphotungstate (PPA-PT) ion-associate in a poly(vinyl chloride) (PVC) membrane plasticized with dioctylphethalate (DOP) or dibutylphethalate (DBP), have been constructed. The electrodes were fully characterized in terms of the membrane composition, temperature, and pH. The electrodes were applied to the potentiometric determination of PPA.Cl in pure solutions and in pharmaceutical preparations under batch and flow injection conditions. The sensors showed fast, stable, and Nernstian slope over the concentration ranges 1.0×10⁻⁵ to 8.91×10⁻³ M and 10⁻⁵ to 10⁻² M in the case of PPA-TPB applying batch and flow injection analysis (FIA), respectively, and 5.01×10⁻⁶ to 1.25×10⁻³ M and 10⁻⁵ to 10⁻² M in the case of PPA-PT for batch and FIA systems, respectively. The electrodes exhibited good selectivity for PPA.Cl with respect to a large number of inorganic cations, sugars, amino acids, and components other than phenylpropanolamine of the mixed drugs. The effect of temperature on the electrodes was also studied.     

Flow injection potentiometric determination of clobutinol hydrochloride

New clobutinol (Clob) ion-selective polyvinyl chloride (PVC) membrane electrodes, based on the ion-associates of Clob with phosphotungstic acid or phosphomolybdic acid were prepared using dibutyl phthalate as plasticizing solvent. The electrodes were characterized in terms of membrane composition, temperature and pH. The sensors showed a near-Nernstian response over the concentration ranges (6.31 × 10⁻⁶)-(1.00 × 10⁻²) and (5.01 × 10⁻⁵)-(1.00 × 10⁻²) M in the case of clobutinol-phosphotungstate ((Clob)₃-PT) applying batch and flow injection (FI) analysis, respectively, and (1.58 × 10⁻⁵)-(1.00 × 10⁻²) and (5.01 × 10⁻⁵)-(1.00 × 10⁻²) M in case of clobutinol-phosphomolybdate ((Clob)₃-PM) for batch and FI analysis systems, respectively. The electrodes were successfully applied for the potentiometric determination of ClobCl in pharmaceutical preparation and urine in steady state and flow injection conditions. The electrodes exhibit good selectivity for Clob with respect to a large number of inorganic cations, sugars and amino acids.     

Screen-printed sensor for batch and flow injection potentiometric chromium(VI) monitoring

A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite–epoxy composite. The optimal graphite–epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 ± 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO₃ solution at pH 3 as the carrier, a flow rate of 2.5 mL·min⁻¹, and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 × 10⁻⁷ M) and online analysis (9.4 × 10⁻⁷ M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills.     

Novel monohydrogenphosphate sensor based on vanadyl salophen

A novel PVC-based membrane sensor based on vanadyl salophen (VNSP) for determination of trace amounts of monohydrogenphosphate (MHP) ions is introduced. The electrode revealed Nernstian response towards monohydrogenphosphate over the wide concentration range from 1.0×10⁻¹ to 1.0×10⁻⁶ M at the pH of 8.2. The effect of solvent mediator, cationic additives and amount of ion-carrier on the behavior of the sensor was investigated. The sensor shows a short response time (<20 s) in the whole concentration ranges. The selectivity of the electrode is very high, and it can be used for detection of trace amounts of monohydrogenphosphate in the presence of large amounts of other anions. The detection limit of the electrode was 5.0×10⁻⁷ M (48 ng/ml) and it could be used for 14 weeks without any measurable changes in the slope. The potentiometric selectivity coefficients data revealed negligible interference from 16 common anions. It was successfully applied for the direct determination of monohydrogenphosphate in fertilizer samples and, as an indicator electrode, in potentiometric titration of HPO₄²⁻ ion with barium nitrate.     

Ionic liquid-based miniature electrochemical sensors for the voltammetric determination of catecholamines

Screen-printed electrodes modified with carbon paste that consisted of graphite powder dispersed in ionic liquids (IL) were used for the electrochemical determination of dopamine, adrenaline and dobutamine in aqueous solutions by means of cyclic voltammetry. The IL plays a dual role in modifying compositions, acting both as a binder and chemical modifier (ion-exchanger); ion-exchange analyte pre-concentration increases analytical signal and improves the sensitivity. Calibration graphs are linear in concentration range 3.9 × 10⁻⁶ to 1.0 × 10⁻⁴ M (dopamine), 2.9 × 10⁻⁷ to 1.0 × 10⁻⁴ M (adrenaline) and 1.7 × 10⁻⁷ to 1.0 × 10⁻⁴ M (dobutamine); detection limits are (1.2 ± 0.1) × 10⁻⁶, (1.3 ± 0.1) × 10⁻⁷ and (5.3 ± 0.1) × 10⁻⁸ M, respectively. Using an additive of Co (III) tetrakis-(tert-butyl)-phthalocyanine leads to the increase of signal and lowering detection limit. Some practical advises concerning both the sensor design and selectivity of catecholamine determination are provided.     

A selective and sensitive carbon composite coated platinum electrode for aluminium determination in pharmaceutical and mineral water samples

A novel coated wire electrode (CWE) for Al(III) ions is described based on 2-(1H-benzo[d]imidazole-1-yl)-1-phenylethanoneoxime as a new ionophore in carbon-PVC composite. The sensor exhibits significantly enhanced selectivity toward Al³⁺ ions over the concentration range 4.3 × 10⁻⁷ to 5.0 × 10⁻² M with a lower detection limit of 2.5 × 10⁻⁷ M and a Nernstian slope of 19.41 ± 0.52 mV decade⁻¹ of aluminium activity. This sensor has a short response time of about 10 s and is reproducible and stable for at least forty-five days. This proposed CWE which is designed for the first time revealed good selectivity for Al(III) over a wide variety of other cations. The performance of the sensor is best in the pH range of 3.1-5.5 and it also works well in partially non-aqueous medium. Moreover, the assembly has been successfully used as an indicator electrode in the potentiometric titration of aluminium (III) against EDTA and also in determining Al(III) quantitatively in pharmaceutical and mineral water samples.     

Ion imprinted polymer based ion-selective electrode for the trace determination of dysprosium(III) ions

Ion-selective electrode (ISE) was designed by dispersing the dysprosium(III) IIP particles in 2-nitrophenyloctyl ether plasticizer and then embedded in polyvinyl chloride matrix. The ISE shows a Nernstian response for dysprosium(III) over a wide concentration range (8.0 × 10⁻⁶ to 1.0 × 10⁻¹ M) with a slope of 21.7 mV per decade. The limit of detection was 2 × 10⁻⁶ M. This sensor has a very fast response time (∼10 s) and offers high selectivity compared to conventional chemical sensors towards dysprosium(III) with respect to several alkali, alkaline earth and transition metal ions as the selectivity is 10-100-fold better. The sensor was used for determination of dysprosium(III) ions by potentiometric (EDTA) titration and has been successfully demonstrated for the determination of fluoride in mouth wash solution.     

Syntheses and evaluation of 7-deoxycholic amide-based tweezer-type copper(II) ion-selective ionophores

Seven tweezer-type copper(II) ion-selective ionophores; that is, 3α,12α-bis[[[N-(R)thiocarboxamino]acetyl]oxy]-N,N-dioctyl-5β-cholan-24-amides and 3α,12α-bis[[[N-(R)thiocarboxaminomethyl]acetyl]oxy]-N,N-dioctyl-5β-cholan-24-amides (R = alkyl and phenyl), were newly designed and synthesized. Their potentiometric evaluation of the poly(vinyl chloride) (PVC) membranes showed excellent affinity and selectivity to copper(II) ions over those of other transition metal ions and alkali/alkaline earth metal ions. These membranes exhibited super-Nernstian responses toward copper(II) ions (34-36 mV/decade), with detection limits of 10⁻⁶-10⁻⁷ M.