Wagiha H. Mahmoud

A novel potassium ion membrane sensor based on rifamycin neutral ionophore.

A novel potentiometric membrane sensor for potassium ion based on the use of rifamycin as a neutral ionophore is described. The sensing membrane is formulated with 2 wt.% rifamycin-SV, 69 wt.% dibutylsebacate plasticizer and 29 wt.% PVC. Linear and stable potential response with near-Nernstian slope of 56.7 +/- 0.2 mV decade(-1) are obtained over the concentration range 1 x 10(-1)-3 x 10(-5) M K(+). The detection limit is 0.3 microg ml(-1) K(+), the response time is 10-30 s and the working pH range is 4-11. Responses of the sensor toward alkali and alkaline earth metal ions are in the order K(+) > Rb(+) > Cs(+) > Na(+) > NH(4)(+) > Ba(2+) > Mg(2+) > Ca(2+) > Sr(2+) > Li(+). The selectivity coefficient data reveal negligible interference from transition metal ions. Direct potentiometric determination of K(+) in the presence of 10-50-fold excess of alkali and alkaline earth metals gives results with an average recovery of 99.1%, and a mean standard deviation of 1.2%. The data agree fairly well with those obtained by flame photometry.

Determination of ranitidine in pharmaceutical preparations using manual and flow injection potentiometry and spectrophotometry

Abstract New, simple and convenient potentiometric and spectrophotometric methods are described for the determination of ranitidine. The potentiometric technique is based on direct measurements of the drug cation with novel PVC matrix membrane sensors incorporating ranitidine-reineckate, tungstophosphate and tungstosilicate ion association complexes as electroactive compounds with 2-nitrophenyl phenyl ether as plasticizing solvent mediator. These sensors exhibit rapid near-Nernstian stable responses for 10−2 − 10−6 M ranitidine over the pH range 4–8, and are used in a flow-through sandwich cell for flow injection determination of the drug. The spectrophotometric method involves the formation of a yellow di(N-nitroso)ranitidine chromophore by reaction of ranitidine with excess nitrite in acetate buffer of pH 4.8 and in the presence of Cu 2+ Br − or micelles as catalyst. Beers law is obeyed at 450 nm over the range 0.3–12 mg ml−1. Determination of ranitidine in a variety of pharmaceutical dosage forms using the proposed potentiometric and spectrophotometric methods shows an average recovery of 98.4% of the nominal values and a mean standard deviation of 0.5%. No interferences are caused by various drug excipients and diluents. The results compare favourably with those obtained by the liquid Chromatographic method of the US Pharmacopoeia.

Ribonucleic acid as a novel ionophore for potentiometric membrane sensors of some transition metal ions

Ribonucleic acid (RNA) is used as a novel ionophore in plasticized poly(vinyl chloride) matrix membrane sensors for some transition metal ions. Membranes incorporating RNA and doped in Cu(2+), Cd(2+) and Fe(2+) display fast near-Nernstian and stable responses for these ions with cationic slopes of 31.1, 31.3 and 35.5 mV per decade, respectively, over the concentration range 10(-6)-10(-2) M and pH range 4-6.5. The cadmium RNA-based sensor shows no interference by Cu(2+), Fe(2+) Hg(2+) and Ag(+), which are known to interfere significantly with the solid-state CdS/Ag(2)S membrane electrode. The copper RNA-based sensor displays general potentiometric characteristics similar to those based on macrocyclic ionophores and organic ion exchangers and has the advantage of a better selectivity for Cu(2+) over some alkaline earth, divalent and transition metal ions. The iron RNA-based membrane sensor exhibits no interference by Hg(2+) and Zn(2+), which are known to interfere with other previously suggested sensors. The nature and composition of the RNA ionophore and its cadmium complex are examined using electrophoresis, Fourier-transform infrared analysis, elemental analysis and X-ray fluorescence techniques.

Extraction-spectrophotometric determination of iron(II) by ternary complex formation with pyrocatechol violet and cetyltrimethylammonium bromide

A method for iron(II) determination based on reaction with Pyrocatechol Violet to form a 1:2 binary complex at pH 5-7 is described and has been extended to an extraction-spectrophotometric procedure for the determination of iron(II) by formation of the 1:2:2 iron(II)-Pyrocatechol Violet-cetyltrimethylammonium bromide ternary complex. The molar absorptivities of the binary and ternary complexes at 595 and 605 nm are 6.55 x 10(4) and 1.35 x 10(5)1.mole(-1).cm(-1), respectively. The method has been successfully applied to the determination of iron in felspar, Portland cement and sodium hydroxide.

PVC matrix membrane electrodes based on cobalt and nickel phenanthroline complexes for selective determination of cobalt(II) and nickel(II) ions

Potentiometric sensors for determining cobalt and nickel ions are described. They are based on the use of cobalt and nickel tris(1,10-phenanthroline)-TPB as electroactive compounds dispersed in plasticized poly(vinyl chloride) matrix. The sensors exhibit fast, near-Nernstian responses for cobalt and nickel-phenanthroline cations over the pH range 3–11 with a slope of 30.3 ± 0.3 mV/concentration decade. In the presence of excess 1,10-phenanthroline reagent, cobalt(II) and nickel(II) ions at concentration levels as low as 4 × 10−6M are accurately determined. The results show an average metal ion recovery of 98.5% with a mean standard deviation of 0.5%. Cobalt in organometallic compounds and nickel in silicate rocks are determined by these sensors and results agreeing fairly well with atomic absorption spectrometry are obtained.

Biomimetic ciprofloxacin sensors made of molecularly imprinted network receptors for potential measurements

A molecularly imprinted polymer (MIP), with special molecule recognition properties of ciprofloxacin CIP), was prepared by thermal polymerization in which ciprofloxacin acted as the template molecule, methacrylic acid (MAA), acrylonitrile (AN) and 2-vinylpyridine (2-VP) acted as the functional monomer and ethylene glycol dimethacrylate (EGDMA) acted as the crosslinker. A biomimetic potentiometric field monitoring device was developed for the assessment of cirofloxacin (CIP) antibiotics based on these newly synthezised imprinted polymers. The sensing elements were fabricated by the inclusion of CIP imprinted polymers in polyvinyl chloride (PVC) matrix. The sensors showed a high selectivity and a sensitive response to the template in an aqueous system. Electrochemical evaluation of these sensors revealed near-Nernstian response with slopes of 29.9 ± 0.7, 27.9 ± 0.5, and 30.3 ± 0.8 mV decade−1 with a detection limit 41.3, 46.3, and 32 μg mL−1CIP with MIP/MAA, MIP/2-VP and MIP/AN membrane based sensors plasticized with DOP, respectively. The effects of lipophilic salts and various foreign common ions were tested. The sensors were easily used in a single channel flow injection system and compared with a tubular detector. The intrinsic characteristics of the detectors in a low dispersion manifold were determined and compared with data obtained under a hydrodynamic mode of operation. Significantly improved accuracy, precision, response time, stability, selectivity and sensitivity were offered by these simple and cost-effective potentiometric sensors compared with other standard techniques. The method had the requisite accuracy, sensitivity and precision to assay CIP in pharmaceutical formulations and biological fluids.

The synthesis, spectral and magnetic properties of the complexes of chromium with chrysenequinone and chrysenequinonemonoxime☆

Abstract Reactions of the chromium hexacarbonyl with chrysenequinone and chrysenequinonemonoxime gave the tris(chrysenesemiquinone)chronium(III), Cr(ChrySQ) 3 , and tris(chrysenesemiquinonemonoxime)chromium(III), Cr(ChrySQM) 3 , complexes. From the stretching frequencies of the carbonyl groups in the IR spectra of the complexes, it was concluded that the ligands bonded to the metal in the semiquinone form. Also, the electronic absorption spectra of the two complexes showed strong UV bands due to metal-to-ligand charge transfer. The magnetic susceptibility determination for the Cr(ChrySQ) 3 complex at 300 K gave a value of 3.261 × 10 −6 e.m.u.g −1 with an effective magnetic moment (μ eff ) of 2.55 μ B . Investigation of Cr(ChrySQ) 3 and Cr(ChrySQM) 3 by EPR spectroscopy at room temperature showed isotropic g values of 1.997 and 1.991 for the two complexes, respectively. The isotropic g values are greater than those observed previously for various o semiquinone chromium complexes. Chrysenequinonemonoxime reacted with Cr(NO 3 ) 3 to give the bis(chrysenequinonemonoximato) (chrysenequinonemonoxime)chromium(III)nitrate. Spectroscopic studies of the complex suggested that the chrysenequinonemonoxime ligand is attached to the metal in both nitroso and oxime forms. Examination of the chromium complexes by cyclic voltammetry showed some reversible or quasireversible redox reactions due to tautomeric interconversions of the semiquinone—catechol couples through electron transfer.

Miniaturized Verapamil Soild-State Potentiometric Sensors Based on Native Ionic Polymers

Abstract. Novel miniaturized carboxylated poly(vinyl chloride) and poly fluoro sulfonate (Nafion) matrix membrane sensors in an all-solid state graphite support were developed, electrochemically evaluated and used for the assay of verapamil drug. These sensors incorporate the native polymers without plasticizer and/or drug-ion pair complex. Upon soaking these sensors in verapamil test solution, electroactive self regenerated membranes are formed and a near-Nernstian potentiometric response is induced for verapamil over the concentration range 1×10−2–1×10−5 M with a cationic slope of 56–57 mV decade−1 of concentration. Inherent advantages of these sensors include fast response (<10 s), long life time (>6 months), good thermal stability (up to 60 °C), high sensitivity (down to 1 μg ml−1), extended working pH range (2–8) and reasonable selectivity. Verapamil could be determined in various dosage forms with an average recovery of 98.8% (st.dev. 0.8%) of the nominal concentration without any significant interferences from various excipients and diluents commonly used in drug formulations.

Determination of iron in aluminium and nickel metals, non-ferrous alloys, feldspar and Portland cement using morin and Triton X-100

A simple and rapid spectrophotometric method for the determination of iron in aluminium and nickel metals, non-ferrous alloys, feldspar and Portland cement is described. The procedure is based on the formation of an iron(III)-morin-Triton X-100 ternary complex at pH 2.6–4. The ternary complex has a molar absorptivity of 6.15 × 104 l mol–1 at 418 nm. The system adheres to Beers law up to 1.1 µg ml–1 of Fe and Sandells sensitivity is 0.0009 µg cm–2 of Fe. The effect of morin and Triton X-100 concentrations, pH, standing time, foreign ions and stoicheiometry are evaluated. The results of the analyses of some synthetic mixtures and standard samples are reported.

Spectrophotometric determination of iron in aluminium metal and some non-ferrous alloys

A new, sensitive and selective spectrophotometric method is suggested for the determination of traces of iron(III) based on complex formation with hematoxylin in presence of cetyltrimethylammonium bromide (CTAB). Addition of CTAB shifted the absorption maximum of the iron-hematoxylin complex from 630 to 640 nm and increased its molar absorptivity from 9.88 × 104 to 1.16 × 105 1·mol−1·cm−1. The method adhered to Beers law up to 0.4 and 0.2 μg/ml of iron in presence and absence of CTAB, respectively. The corresponding values of Sandells sensitivity were 0.5 and 0.6 ng·cm−2. The effect of reagent and surfactant concentrations, pH and standing time were investigated. EDTA, tartrate and sodium fluoride were used as masking agents for most of the interfering ions. The method was successfully used for the determination of iron in aluminium metal and some non-ferrous alloys.