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

New pseudoephedrine selective electrodes have been constructed of the conventional polymer membrane type by incorporation of pseudoephedrine-phosphotungstate (PE-PT) or pseudoephedrine-silicotungstate (PE-SiT) ion-associates in a poly vinyl chloride (PVC) membrane plasticized with dibutyl phthalate (DBP). The electrodes were fully characterized in terms of the membrane composition, temperature, and pH. The electrodes exhibited mean slopes of calibration graphs of 57.09 and 56.10 mV concentration decade(-1) of PECl at 25 degrees C for (PE-PT) and (PE-SiT) electrodes, respectively. The electrodes showed fast, stable, and near-Nernstian response over the concentration ranges 6.31 x 10(-6)-1.00 x 10(-2) and 5.00 x 10(-5)-1.00x10(-2) M in the case of PE-PT applying batch and flow injection (FI) analysis, respectively, and 1.00 x 10(-5)-1.00 x 10(-2) and 5.00 x 10(-5)-1.00x10(-2) M in the case of PE-SiT for batch and FI analysis system, respectively. Detection limit was 5.01x 10(-6) M for PE-PT electrode and 6.31x10(-6) M for PE-SiT electrode. The electrodes were successfully applied for the potentiometric determination of pseudoephedrine hydrochloride (PECl) in pharmaceutical preparations with mean recovery 101.13 +/- 0.85% and 100.77+0.79% in case of PE-PT applying batch and flow injection systems, respectively, and 100.75+0.85% and 100.79 +/- 0.77% in case of PE-SiT for batch and flow injection systems, respectively. The electrodes exhibited good selectivity for PECl with respect to a large number of inorganic cations, sugars and amino acids.     

Construction and performance characteristics of new tetramisole selective plastic membrane electrodes

New tetramisole (Tm) ion selective PVC membrane electrodes are constructed based on either the ion-pair complex Tm TPB (Electrode I) where TPB is tetraphenylborate or the ion associate Tm(3) PT (Electrode II) where PT is phosphotungstate. The rectilinear concentration ranges of Electrodes I and II are 4 x 10(-5)-10(-2)M (average slope = 55.7 mV/concentration decade) and 5 x 10(-5)-10(-2)M TmCl (average slope = 57.0 mV/concentration decade), at 25 degrees C, respectively. The life time of the two Electrodes I and II are 14 and 49 days of continuous working, respectively. The change in pH does not affect the electrodes performance within the range 3.0-5.5, 3.0-6.0 and 3.0-7.0 for Tm concentrations 10(-2) 5 x 10(-3) and 10(-3)M, respectively. The isothermal coefficients of Electrodes I and II are found to be 0.000667 and 0.001164 V/ degrees C, respectively. The electrodes proved to be highly selective for TmCl towards inorganic cations, sugars and amino acids. The standard addition method and potentiometric titration are used to determine Tm in pure solutions and in tetramisole 10% oral solution. Regeneration process for the exhausted Electrodes I and II is applied successfully by soaking them in a solution of NaTPB and PTA, respectively.     

Papaverine PVC membrane ion-selective electrodes based on its ion-exchangers with tetraphenylborate and tetrathiocyanate anions

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1 x 10(-2) to 6 x 10(-5) M and 1 x 10(-2) to 1 x 10(-5) M for PA-TPB and PA-TTC respectively at 25 degrees C over the pH range of 3-5.0 with a cationic slope of approximately 56.5 +/- 0.5 mV/decade for both sensors respectively. The lower detection limit is 4 x 10(-5) and 8 x 10(-6) M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0- 3000.0 microg/ml of PA in aqueous solutions shows an average recovery of 99.1% and a mean relative standard deviation of 1.4 at 100microg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.     

New conventional coated-wire ion-selective electrodes for flow-injection potentiometric determination of chlordiazepoxide.

New chlordiazepoxide hydrochloride (Ch-Cl) ion-selective electrodes (conventional type) based on ion associates, chlordiazepoxidium-phosphomolybdate (I) and chlordiazepoxidium-phosphotungstate (II), were prepared. The electrodes exhibited mean slopes of calibration graphs of 59.4 mV and 60.8 mV per decade of (Ch-Cl) concentration at 25 degrees C for electrodes (I) and (II), respectively. Both electrodes could be used within the concentration range 3.16 x 10(-6)-1 x 10(-2) M (Ch-Cl) within the pH range 2.0-4.5. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficients of the electrodes, which were 0.00139 and 0.00093 V degrees C(-1) for electrodes (I) and (II), respectively. The electrodes showed a very good selectivity for Ch-Cl with respect to the number of inorganic cations, amino acids and sugars. The electrodes were applied to the potentiometric determination of the chlordiazepoxide ion and its pharmaceutical preparation under batch and flow injection conditions. Also, chlordiazepoxide was determined by conductimetric titrations. Graphite, copper and silver coated wires were prepared and characterized as sensors for the drug under investigation.     

Anion selective polymeric membrane electrodes based on cyclopalladated amine complexes

The potentiometric anion selectivity of two polymer membrane based electrodes (I and II) formulated with two new cyclopalladated amine complexes as the active components are examined. The electrodes exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response towards thiocyanate, iodide and nitrite. The graph potential versus log c is linear over the concentration range 10(-6)-6x10(-2) M thiocyanate with electrode I and 10(-6)-10(-3) M with electrode II; 10(-5)-10(-2) M iodide with electrode I and 10(-3)-6x10(-2) M with electrode II; and 10(-3)-6x10(-2) M nitrite with both electrodes. The influence of the plasticizer and pH are studied. The potentiometric selectivity coefficients for I, II and blank membrane electrodes are reported. The selective interaction between Pd(II) thiocyanate, iodide and nitrite is postulated to be the reason for its higher response.     

A Novel Screen-Printed and Carbon Paste Electrodes for Potentiometric Determination of Uranyl(II) Ion in Spiked Water Samples

Four new ion-selective electrodes (ISEs) based on poly-(1-4)-2-amino-2-deoxy-β-D-glucan (chitosan) ionophore were constructed for determination of uranyl ion (UO₂(II)) over wide concentration ranges. The linear concentration range for carbon paste electrodes (CPEs) was 1 × 10^–6–1 × 10^–2 mol/L with a detection limit of 1 × 10^–6 mol/L and that for the screen-printed electrode (SPEs) was 1 × 10^–5–1 × 10^–1 mol/L with a detection limit of 8 × 10^–6 mol/L. The slopes of the calibration graphs were 29.90 ± 0.40 and 29.10 ± 0.60 mV/decade for CPEs with dibutylphthalate (DBP) (electrode I) and o-nitrophenyloctylether (o-NPOE) (electrode II) as plasticizers, respectively. Also, the SPEs showed good potentiometric slopes of 29.70 ± 0.30 and 28.20 ± 1.20 mV/decade with DBP (electrode III) and o-NPOE (electrode IV), respectively. The electrodes showed stable and reproducible potential over a period of 54, 62, 101 and 115 days for electrodes I, II, III, and IV, respectively. The electrodes manifested advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations except Ce(III) ion which interfere seriously. The results obtained compared well with those obtained using atomic absorption spectrometry.     

1‐Pyrrolidine Dicarbodithioate Based Electrodes for Determination of Iron(III) in Lubrication Oil

The lipophillic ammonium salt of 1‐pyrrolidine dicarbodithioic acid (PCDT) (I) was introduced as a new selective ionophore for an iron selective electrode. In addition, the effect of immobilization of 18‐crown‐6 (18CE6) (membrane type‐II), on the electrode performance was discussed. The slope of the PCDT‐based (I) electrode was (20 mV/decade). The linear concentration range was (10^?5–10^?1 M) after one day doping. The detection limit for electrode type‐(II) was (1.3×10^?6 M). For membrane with only 18CE6 (type‐III) the linear range and the detection limit were improved (10^?5–10^?1 M and 3.2×10^?6 M, respectively). The pH‐range was between 5–11 for type‐II, and III electrodes, while it was 7–11 for type‐I electrode. Most of the common cations were tested for the evaluation of the electrode selectivity with correlation to the ionic radii of the tested cations. Among them only Ag⁺ and Pb²⁺ were the real interference for type‐III electrode. Application of using the electrode for the determination of iron in lubrication oil samples was performed with RSD (1.77–2.7%) and (1.01–2.3%) for type‐II and III electrodes, respectively. The corresponding recovery ranges were (93.0–99.9%) and (96.3–100%). The obtained results were compared to those of an atomic absorption spectrophotometric method.     

Ion-selective electrodes for potentiometric determination of ranitidine hydrochloride, applying batch and flow injection analysis techniques.

New ranitidine hydrochloride (RaCl)-selective electrodes of the conventional polymer membrane type are described. They are based on incorporation of ranitidine-tetraphenylborate (Ra-TPB) ion-pair or ranitidine-phosphotungstate (RaPT) ion-associate in a poly(vinyl chloride) (PVC) membrane plasticized with dioctylphthalate (DOP) or dibutylphthalate (DBP). The electrodes are fully characterized in terms of the membrane composition, solution temperature, and pH. The sensors showed fast and stable responses. Nernstian response was found over the concentration range of 2.0 x 10(-5) M to 1.0 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-TPB electrode and over the range of 1.03 x 10(-5) M to 1.00 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-PT electrode for batch and FIA systems, respectively. The electrodes exhibit good selectivity for RaCl with respect to a large number of common ions, sugars, amino acids, and components other than ranitidine hydrochloride of the investigated mixed drugs. The electrodes have been applied to the potentiometric determination of RaCl in pure solutions and in pharmaceutical preparations under batch and flow injection conditions with a lower detection limit of 1.26 x 10(-5) M and 5.62 x 10(-6) M at 25 +/- 1 degrees C. An average recovery of 100.91% and 100.42% with a relative standard deviation of 0.72% and 0.53% has been achieved.     

Etilefrine Plastic Membrane Electrodes Based on Individual and Mixed Ion-exchangers of Etilefrinium Phosphotungstate and Tetraphenylborate.

Abstract

Etilefrine hydrochloride (EfCl) selective PVC membrane electrodes based on Etilefrinium phosphotungstate (I), Etilefrinium tetraphenylborate (II) and a mixture of both (III) were prepared, The electrodes exhibited near Nernstian response over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?1, 6.3 × 10^?6 - 1.0 × 10^?1 and 6.3 × 10^?5 - 1.0 × 10^?1 M EfCl for electrodes I, II and III, respectively. The working pH ranges of electrodes I, II and III were 10 - 8.0, 10 - 7.5 and 10 - 7.5 and their isothermal coefficients were 0.00150, 0.00088 and 0.00072 V/°C, respectively. The electrodes showed good selectivity to EfCl with respect to many inorganic cations, sugars and amino acids. The standard additions method was used to determine EfCl in pure solutions and in pharmaceutical preparations.     

Copper(II) modified carbon paste electrodes based on self-assembled mercapto compounds-gold-nanoparticle

Three mercapto compounds [2-mercapto-5-(1-methyl-5-nitroimidazole-2-yl)-1,3,4-thiadiazole] (MMNIT), [2-mercapto-5-(5-nitrofuran-2-yl)-1,3,4-thiadiazole] (MNFT) and [2-mercapto-5-(5-nitrothiophen-2-yl)-1,3,4-thidiazole] (MNTT) were used for self-assembled-gold nanoparticle (SAGNP) modified carbon paste electrodes. The electrodes were applied as indicator electrodes for potentiometric determination of Cu(II) ion. The prepared electrodes exhibit a Nernstian slope of 31.0+/-0.5 mV per decade for Cu(II) ion over a wide concentration range of 7.9x10(-9)-3.2x10(-2), 7.9x10(-9)-7.9x10(-4), and 2.8x10(-8)-7.9x10(-3) mol L(-1) for MMNIT, MNFT and, MNTT, respectively. The detection limits of electrodes were 3.5 (+/-0.2)x10(-9), 4.1x10(-9), and 4.1x10(-8) mol L(-1) of copper ion, respectively. The potentiometric responses of electrodes based on MMNIT, MNFT, and MNTT are independent of the pH of test solution in the pH range 2.0-5.5, 2.5-7.0, and 2.0-6.5, respectively. They have quick response with response time of about 5 s. The proposed electrodes show fairly good selectivity over some alkali, alkaline earth, transition and heavy metal ions. Finally, the proposed electrodes were successfully employed to detect Cu(II) ion in hair and water samples.     

Uranyl-selective PVC membrane electrodes based on some recently synthesized benzo-substituted macrocyclic diamides

Four different recently synthesized macrocyclic diamides were studied to characterize their abilities as uranyl ion carriers in PVC membrane electrodes. The electrodes based on macrocycle 1,18-diaza-3,4;15,16-dibenzo-5,8,11,14,21,24-hexaoxacyclohexaeicosane-2,17-dione resulted in a Nernstian response for UO(2)(2+) ion over wide concentration ranges. The linear concentration range for the polymeric membrane electrode (PME) is 3.0x10(-6)-8.2x10(-3) M with a detection limit of 2.2x10(-6) and that for the coated graphite electrode (CGE) is 5.0x10(-7)-1.5x10(-3) M with a detection limit of 3.5x10(-7) M. The electrodes manifest advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations.     

Voltammetric determination of mercury(II) at a carbon paste electrode in aqueous solutions containing tetraphenylborate ion

The determination of mercury(II) ions can be achieved by monitoring the decrease in the oxidation peak of the tetraphenylborate ion in the presence of this metal ion at a carbon paste electrode. The reaction between mercury(II) and the tetraphenylborate ion results in the formation of diphenylmercury, thus providing the method with good selectivity over other metal ions. Using anodic stripping voltammetry in a neutral electrolyte, a linear dependence of the decrease of peak height was observed on increasing the mercury(II) concentration in the range 1 x 10(-6)-8 x 10(-9)M mercury(II). Zinc(II), cadmium(II), lead(II), nickel(II), cobalt(II), tin(II), potassium(I) and ammonium(I) ions did not interfere at a 1000-fold concentration excess. Iron(III) and chromium(III) did not interfere at a 250-fold and 50-fold concentration excess, respectively. Following masking procedures, copper(II), bismuth(III) and silver(I) did not interfere at a 100-fold concentration excess. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

Potentiometric batch and flow injection analysis of betaine hydrochloride

Novel PVC membrane electrodes for the determination of betaine ion based on the formation of betaine-tetraphenylborate (Be-TPB) and betaine-phosphotungstate (Be-PT) ion-exchangers as electroactive materials are described. The sensors show a fast, stable, near Nernstian response for 6.92 x 10(-6) to 7.94 x 10(-3) M and 1.0 x 10(-4) to 1.0 x 10(-2) M betaine hydrochloride (Be.Cl) in case of Be-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 2.95 x 10(-5) to 2.26 x 10(-3) M and 3.16 x 10(-5) to 1.0 x 10(-2) M in case of Be-PT electrode for batch and FIA electrodes, respectively, at 25 degrees C over the pH range of 3.5-10 with a cationic slope of 60.2 and 59.1 mV decade(-1) and a fast potential response of < or =15 s. The lower detection limits are 7.94 x 10(-6) and 3.18 x 10(-5) M Be.Cl for Be-TPB and Be-PT electrodes, respectively. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components other than betaine, of the mixed drug investigated show negligible interference. The electrodes have been applied to the direct potentiometric determination of betaine hydrochloride in water and in a pharmaceutical preparation under batch and FIA conditions. Potentiometric titrations of Be.Cl with NaTPB and PTA as titrants were monitored with the developed betaine electrodes as an end point indicator electrode. The determination of Be.Cl shows an average recovery of 100.8% with mean relative standard deviation of 0.61%. The effect of temperature on the electrodes was also studied.     

A selective membrane electrode for lanthanum(III) ion based on a hexaaza macrocycle derivative as ionophore.

We have developed a highly La(III)-selective PVC membrane electrode based on a hexaaza macrocycle, 8,16-dimethyl-6,14-diphenyl-2,3,4:10,11,12-dipyridine-1,3,5,9,11,13-hexaazacyclohexadeca-3,5,8,11,13,16-hexaene [Bzo2Me2Pyo2(16)-hexaeneN6] (I) as membrane carrier, dibutylbutyl phosphonate (DBBP) as solvent mediator and sodium tetraphenylborate (NaTPB) as lipophilic additive. The best performance was given by the membrane of macrocycle I having a composition 10:260:5:120 (I:DBBP:NaTPB:PVC). The electrode exhibits a Nernstian response to La(III) ion in the concentration range 1.0x10(-1)-7.94x10(-7) M with a slope of 19.8+/-0.2 mV/decade of concentration and a detection limit of 5.62x10(-7) M. The response time of the sensor is 12 s and it can be used over a period of 4 months with good reproducibility. The electrode works well over a pH range of 2.5-10.0 and in partially non-aqueous medium with up to 30% organic content. The sensor was also used as an indicator electrode in potentiometric titration of La(III) ions with EDTA and for determining La(III) concentration in real samples.     

Chemically modified carbon paste electrode for iodide determination on the basis of cetyltrimethylammonium iodide ion-pair.

A new carbon paste electrode (CPE) for the determination of iodide ion based on a cetyltrimethylammonium iodide (CTMAI) ion pair as an electroactive material is described. The electrode shows a linear response for iodide ion over the concentration range of 4 x 10(-5) M to 1 x 10(-1) M with a lower detection limit of 4 x 10(-5) M at 25 degrees C. The electrode has a Nemstian slope of -55.0 +/- 0.4 mV/decade and a fast potential response of 45 s, which is almost constant over a pH range of 5.0 - 9.0. Selectivity coefficient data of the CTMAI-CPE for some common ions show negligible interference, and the electrode has high selectivity towards the iodide ion. An average recovery of 101.83% with a relative standard deviation of 1.53% has been achieved for the determination of iodide in Flaxedil (gallamine triethiodide) ampoules, a muscle relaxant drug. The electrode has been examined for the determination of iodide in saline water; the results were found to compare favorably with those obtained using Metrohm iodide ISE. The electrode has been utilized as an end-point indicator electrode for the determination of Hg(II) and phenylmercury(I) in their aqueous solutions using potentiometric titration with a potassium iodide standard solution.     

Coated-wire silver ion-selective electrode based on silver complex of cyclam.

A coated-wire ion-selective electrode (ISE) based on cyclam (1,4,8,11-tetraazacyclotetradecane) as a neutral carrier in a polyvinyl chloride (PVC) matrix was fabricated for the determination of Ag(I) ions. The coated-wire ISE exhibited a linear Nernstian response over the range 1 x 10(-1) to 1 x 10(-7) M with a slope of 59 +/- 2 mV per decade change and a detection limit of 5 x 10(-8) M. The ISE shows a greater preference for Ag over other cations with good precision. The electrode was selective towards Ag(I) ions in the presence of 13 different metal ions tested. The selectivity coefficients (K(ij)) were determined for Na(I), K(I), Mg(II), Ca(II), Ba(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II). The selectivity coefficients of these cations are in the range of 10(-4) to 10(-2). This ISE was used for the determination of free silver and total silver in electroplating bath solutions, additives and brighteners.     

Fabrication of PVC based membrane using nickel porphyrazine as ionophore in the screening of thiocyanate ion in aqueous and real samples

The [Ni[(TAP)(SBn)8]] complex (I), i.e. ([2,3,7,8,12,13,17,18-octakis(benzylthio)-5,10,15,20-tetraazaporphyrin])nickel(II), has been explored as an ionophore for fabrication of the PVC based membrane electrodes used in the screening of thiocyanate anion (SCN-). The membrane having [Ni[(TAP)(SBn)8]] complex (I) as an electroactive material and dioctylphthalate (DOP) as plasticizer in the PVC matrix with the percentage ratio 5 : 158 : 200 (I : DOP : PVC, % w/w) exhibited a linear response in the concentration range 7.0 x 10(-6)-1.0 x 10(-1) M of SCN- with a sub-Nernstian slope 32.5 +/- 0.2 mV/decade of activity and a fast response time of 10 +/- 2 s. The sensor works well in the pH range 3.0 - 9.5 and could be satisfactorily used in presence of 50 % (v/v) methanol, ethanol and acetone, and is selective for SCN- over a large number of anions with slight interference from iodide (I-) and azide (N3-) if present at a level >or = 1.0 x 10(-5) M. Described electrode works well over a period of six months. The sensor can be successfully applied for the screening of SCN- in both aqueous and real samples and also as indicator electrodes in precipitation titrations.     

Newly selective electrochemical sensors for trace-level determination of Al(III) ions in drainage water,spiked tap water and pharmaceutical preparation samples

In this work, two newly sensitive and selective Al(III)-modified carbon paste electrodes (MCPEs) were developed based on diphenylcarbazone (DPC) modifier mixed with tricresyl phosphate plasticizer and either graphite powder (electrode I) or graphite powder mixed with graphene (electrode II). The potentiometric performance characteristics of the two electrodes were scrutinized and discussed. The proposed sensors showed a high electrochemical response in the linear concentration range of 1.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹ with a good Nernstian slopes of 20.12 ± 0.30 mV decade⁻¹ and 20.63 ± 0.66 mV decade⁻¹ and limits of detection of 9.0 × 10⁻⁷ and 8.5 × 10⁻⁷ mol L⁻¹ for electrode (I) and electrode (II), respectively. Both electrodes showed a fast response time and reasonable thermal stability. The potentiometric response of the DPC-based electrodes was independent on the pH of the tested solutions in ranges of 2.5–5 and 2.5–5.5 for electrode (I) and electrode (II), respectively. The two electrodes can be also used in partially non-aqueous medium containing up to 20% (v/v) acetone or methanol with no significant changes in the working concentration ranges or the slopes. The proposed electrodes showed fairly good discriminating ability toward Al(III) ions in comparison with many other metal ions. The electrodes were applied successfully for Al(III) ions determination in drainage water, spiked tap water and pharmaceutical preparation samples. Furthermore, the electrode surfaces were characterized using energy-dispersive X-ray (EDX) and scanning electron microscopic (SEM) as surface characterization techniques and Fourier Transform Infrared (FT-IR) technique to confirm the interaction between Al(III) and DPC.

     

Highly selective PVC-membrane electrodes based on Co(II)-Salen for determination of nitrite ion.

A cobalt(II) derivative was used as a suitable ionophore for the preparation of a polymeric membrane nitrite-selective electrode. The electrode reveals a Nemstian behavior over a very wide NO2- ion concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) and a very low detection limit (5.0 x 10(-7) M). The potentiometric response is independent of the pH of solution in the pH range 4.0-9.5. The electrode shows advantages such as low resistance, fast response and, most importantly, good selectivity relative to a wide variety of inorganic and organic anions. In fact, the selectivity behavior of the proposed NO2- ion-selective electrode shows great improvements compared to the previously reported electrodes for nitrite ion. The proposed electrodes could be used for at least 2 months without any significant changes in potentials. The electrode was successfully applied to the determination of nitrate ion concentrations in sausage and milk samples.     

Potentiometric carbon paste sensors for lead(II) based on dithiodibenzoic and mercaptobenzoic acids.

Dithiodibenzoic (DTB) acid and mercaptobenzoic (MB) acid were studied to characterize their abilities as modifier agents for lead(II) sensors. For both sensors, the best results were obtained with modified carbon paste electrodes with 24.1% of ligand. The pH influence on the potentiometric response was studied. The selectivity coefficients for both modified electrodes were tabulated. A potentiometric sensor based on DTB acid exhibited a more sensitive and selective response to lead ions than an MB electrode. The limits of detection for the DTB and MB electrodes were very similar, 5.01 x 10(-8) M and 3.98 x 10(-8) M, respectively, for lead(II) activity. The DTB sensor was applied to lead(II) ion determination in real samples and as an indicator electrode in potentiometric titrations. Natural and commercial humic acids were titrated using the DTB electrode to estimate the stability constant between these organic compounds and the lead(II) ions with successful results.