Tamer Awad Ali

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 x 10(-2) to 1 x 10(-6) M CPC at 25 degrees C over the pH range 2-8 with cationic slope 60.66+/-1.10. The lower detection limit is found to be 8 x 10(-7) M and response time of about 3s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D.=0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.

Synthesis of some quaternary ammonium gemini surfactants and evaluation of their performance as corrosion inhibitors for carbon steel in oil well formation water containing sulfide ions

Three quaternary ammonium gemini surfactants were synthesized, characterized, and evaluated as corrosion inhibitors for carbon steel in oil well formation water containing sulfide ions. The corrosion inhibition efficiency was measured by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The data obtained from EIS were analyzed to model the corrosion inhibition process through an equivalent circuit. The Tafel polarization results indicate that the inhibitors act as mixed type inhibitors. The nature of the protective film formed on the carbon steel surface was studied using scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDX). The effect of molecular structure on the inhibition efficiency was investigated by quantum chemical calculations. It was found that the inhibition efficiency increased with increasing length of the alkyl group attached to the tertiary nitrogen atom. The values of standard adsorption equilibrium constant and free energy of adsorption for the three inhibitors were calculated and discussed. The adsorption of the inhibitor molecules on carbon steel surface was found to follow the Langmuir adsorption isotherm.

Novel screen-printed electrode for the determination of dodecyltrimethylammonium bromide in water samples.

The construction and electrochemical response characteristics of a screen-printed electrode (SPE) for the determination of dodecyltrimethylammonium bromide (DTAB) are described. The sensor was based on the use of DTA-tetraphenylborate ion association complex as an electroactive material in screen-printed electrode with dioctylsebacate (DOS) as a solvent mediator. In aqueous solution of pH 3, the sensor displayed a stable response for six months with reproducible potential and linear response for surfactant over the concentration range 1.20 × 10(-2) -5.6 × 10(-7) mol L(-1) at 25 °C with Nernstian slope of 55.95 ± 0.58 mV decade(-1) for detection limit of 6.8 x 10(-6) mol L(-1) . The response time was 6-10 s. The selectivity coefficients indicate excellent selectivity for DTAB over many common cations (e.g. Mg(2+), Na(+), K+, Co(2+), Ni(2+), Ca(2+), Cl(-), I(-), SO(4)(-2) and cetylpyridinium chloride (CPC). The sensor was used successfully for the determining of DTAB in pure form and water samples with average recoveries of 99.98, 98.78, and 99.99%.

A New Screen-printed Ion Selective Electrode for Determination of Citalopram Hydrobromide in Pharmaceutical Formulation

Abstract Novel citalopram screen-printed ion selective electrodes were fabricated, characterized and used for the determination of citalopram in pharmaceutical formulations. The proposed sensors incorporated potassium tetrakis( p -chlorophenyl) borate (KTpClPB) ionophore (electrode V) and citalopram-phosphotungstate (CP-PT) ion pair complex (electrode X) as electroactive materials in screen-printed electrodes and tricresylphosphate (TCP) as solvent mediator. The fabricated electrodes demonstrated near Nernstain response over wide linear range of 4.9 × 10 −7 −1.0 × 10 −2 M and 1.0 × 10 −6 −1.0 × 10 −2 M citalopram with lower limit of detection of 4.9 × 10 −7 M and 1.0 × 10 −6 M and slope of (60.47 ± 0.80) mV decade −1 and (59.93 ± 1.45) mV decade −1 for electrode (V) and (X), respectively. The results showed that the proposed sensors had the characteristics such as fast and stable response, good reproducibility, long term stability (5 and 4 months) and applicability over a wide pH range of 2–9 and 2–8 for electrodes (V) and (X). The sensors displayed good selectivity for citalopram with respect to number of common foreign inorganic, organic species, excipients and the fillers added to the pharmaceutical preparation. The sensors were successfully applied for the determination of citalopram in tablet, urine and serum.

Modified screen-printed ion selective electrodes for potentiometric determination of sodium dodecylsulfate in different samples.

Fabrication and general performance characteristics of novel screen-printed sensors for potentiometric determination of sodium dodecylsulfate (SDS) are described. The sensors are based on the use of ion-association complexes of SDS with cetylpyridinium chloride (electrode I) and cetyltrimethylammonium bromide (electrode II) as exchange sites in a screen-printed electrode matrix. Electrodes (I) and (II) show fast, stable, and near-Nernstian response for the mono-charge anion of SDS over the concentration range of 1×10(-2) - 5.8×10(-7) and 1×10(-2)-6.3×10(-7) mol/L at 25°C and the pH range of 2.0-9.0 and 2.0-8.0 with anionic slope of 57.32±0.81 and 56.58±0.65 mV/decade, respectively. Electrodes (I) and (II) have lower LODs of 5.8×10(-7) and 6.3×10(-7) mol/L and response times of about 8 and 13 s, respectively. Shelf life of 5 months for both electrodes is adequate. Selectivity coefficients of SDS related to a number of interfering cations, and some inorganic compounds were investigated. There were negligible interferences caused by most of the investigated species. The direct determination of 0.10-13.50 mg of SDS by electrodes (I) and (II) shows average recoveries of 99.96 and 99.85%, and mean RSDs of 0.83 and 1.04%, respectively. In the present investigation, both electrodes were used successfully as end point indicators for determination of SDS in pure pharmaceutical preparations and real spiked water samples. The results obtained using the proposed sensors to determine SDS in solution compared favorably with those obtained by the standard addition method.

Multi-walled carbon nanotube and nanosilica chemically modified carbon paste electrodes for the determination of mercury(II) in polluted water samples

Novel carbon paste ion selective electrodes based on the 1,4-bis(6-bromohexyloxy)benzene (BHOB) ionophore were constructed in order to determine the Hg(II) ion concentration. Multi-walled carbon nanotubes (MWCNTs) and nanosilica modifiers were used for improving the response characteristics of mercury carbon paste sensors. MWCNTs have good conductivity which helps the transduction of the signal in carbon paste electrodes. These potentiometric sensors respond to Hg(II) ions in wide linear concentration ranges of 1 × 10−1 to 1.0 × 10−7 and 1.0 × 10−1 to 1.8 × 10−8 mol L−1 with Nernstian slopes of 28.75 ± 0.46 and 29.92 ± 0.15 mV decade−1 of Hg(II) ions and detection limits of 1 × 10−7 and 1.8 × 10−8 mol L−1 for the MWCNT-CPE (electrode V) and MWCNT/nanosilica-CPE (electrode VII), respectively. The electrodes were pH independent within the ranges of 3.0–7.5 and 2.5–8.5, with a fast response time of about 7 and 4 s, and can be used for at least 110 and 145 days without any considerable divergence in the potentials of electrode (V) and electrode (VII), respectively. The proposed sensors thus allowed a sensitive, selective, simple, low-cost, and stable electrochemical response to Hg(II) ions in the presence of a large number of alkali, alkaline earth, transition and heavy metal ions. Such abilities promote new opportunities for determining Hg(II) ions in a wide range of real samples. The results obtained were compared with those obtained using inductively coupled plasma atomic emission spectrometry (ICP-AES).

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.

Construction and Performance Characteristics of Modified Screen Printed and Modified Carbon Paste Sensors for Selective Determination of Cu(II) Ion in Different Polluted Water Samples

Four new ion-selective electrodes (ISEs), based on N,N′-bis(salicylaldehyde)-p-phenylene diamine (SPD) as ionophore, are constructed for the determination of copper(II) ion. The modified carbon paste (MCPEs; electrodes I and II) and modified screen-printed sensors (MSPEs; electrodes III and IV) exhibit good potentiometric response for Cu(II) over a wide concentration range of 1.0 × 10−6 – 1.0 × 10−2 mol L−1 for electrodes (I and II) and 4.8 × 10−7–1.0 × 10−2 mol L−1 for electrodes (III and IV) with a detection limit of 1.0 × 10−6 mol L−1 for electrodes (I and II) and 4.8 × 10−7 mol L−1 for electrodes (III and IV), respectively. The slopes of the calibration graphs are 29.62 ± 0.9 and 30.12 ± 0.7 mV decade−1 for electrode (I) (tricresylphosphate (TCP) plasticizer) and electrode (II) (o-nitrophenyloctylether o-NPOE plasticizer), respectively. Also, the MSPEs showed good potentiometric slopes of 29.91 ± 0.5 and 30.70 ± 0.3 mV decade−1 for electrode (III) (TCP plasticizer) and electrode (IV) (o-NPOE plasticizer), respectively. The electrodes showed stable and reproducible potentials over a period of 60, 88, 120, and 145 days at the pH range from 3 to 7 for electrodes (II), (III), and (IV) and pH range from 3 to 6 for electrode (I). This method was successfully applied for potentiometric determination of Cu(II) in tap water, river, and formation water samples in addition to pharmaceutical preparation. The results obtained agree with those obtained with the atomic absorption spectrometry (AAS).