Ashraf A. Mohamed

Highly sensitive and selective catalytic determination of formaldehyde and acetaldehyde

A highly sensitive, simple and selective kinetic method was developed for the determination of ultra-trace levels of formaldehyde and acetaldehyde based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine (DPD) with hydrogen peroxide. The reaction was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of DPD at 510nm, within 30s of mixing the reagents. The optimum reaction conditions were: 20mmolL(-1) DPD, 250mmolL(-1) H(2)O(2), 150mmolL(-1) phosphate, 150mmolL(-1) citrate and pH 6.60+/-0.05 at 25 degrees C. Following the recommended procedure, formaldehyde and acetaldehyde could be determined with linear calibration graphs up to 0.50 and 1.4microg mL(-1) and detection limits, based on the 3S(b)-criterion, of 0.015 and 0.035microg mL(-1), respectively. In addition, analytical data for other 10 aldehydes were also presented. The high sensitivity and selectivity of the proposed method allowed its successful application to rain water, mainstream smoke (MSS) and disposed tips of smoked cigarettes (DTSC). A sample aliquot was directly analyzed for its total water-soluble aldehyde content. A second sample aliquot was heated at 80 degrees C for 10min to expel acetaldehyde and the aliquot was analyzed for its content of other water-soluble aldehydes (expressed as formaldehyde equivalent), and acetaldehyde was determined by difference. The analytical results were in excellent agreements with those obtained following the standard HPLC method based on pre-column derivatization with 2,4-dinitrophenylhydrazine. Moreover, published catalytic-spectrophotometric methods for the determination of aldehydes were reviewed.

Catalytic determination of vanadium using the perphenazine–bromate redox reaction and a citric acid activator

Citric acid was found to have a highly activating effect on the vanadium-catalysed oxidation of perphenazine (PP) with bromate. An extremely sensitive, selective and simple method was developed for the determination of vanadium based on this effect. The reaction rate was followed spectrophotometrically by monitoring the formation of the red oxidation product of PP at 526 nm within 1 min of mixing. Using the recommended procedure, vanadium can be determined up to 6.5 ng ml–1 with a linear calibration graph and a detection limit of 0.08 ng ml–1. A suggested mechanism of the reaction and the activating mechanism of citric acid is presented. The method surpassed the standard Fishman–Skougstad catalytic method in sensitivity, selectivity and speed and was successfully applied to the determination of vanadium in polluted river waters.

A novel kinetic determination of dissolved chromium species in natural and industrial waste water.

A highly sensitive, selective and simple kinetic method was developed for the determination of dissolved chromium species based on the catalytic effect of Cr(III) and/or Cr(VI) on the oxidation of 2-amino-5-methylphenol (AMP) with H(2)O(2). The fixed time and initial rate variants were used for kinetic spectrophotometric measurements by tracing the oxidized product at 400nm for 10min after starting the reaction. Boric acid and Tween-40 exerted pronounced activating and micellar sensitizing effects on the studied redox reaction, respectively. The optimum reaction conditions were: 3.0mmoll(-1) AMP, 0.45moll(-1) H(2)O(2), 0.50moll(-1) boric acid, 4v/v% Tween-40, 10mmoll(-1) phosphate buffer and pH 6.45+/-0.02 at 35 degrees C. Both Cr(III) and Cr(VI) ions exerted the same catalytic effect on the studied reaction. Linear calibration graphs were obtained for the determination of up to 6.0ngml(-1) Cr with detection limits of 0.054 and 0.10ngml(-1) Cr; following the fixed time and initial rate methods, respectively. The proposed method was successfully applied to the speciation and determination of trace levels of dissolved Cr(III) and Cr(VI) in natural and effluents of industrial waste water. The total dissolved Cr(III) and Cr(VI) species was determined first. In a second run, Cr(VI) was determined alone after precipitation of Cr(III) ions in presence of Al(OH)(3) collector, where Cr(III) is then determined by difference. Moreover, published catalytic-spectrophotometric methods for chromium determination were reviewed.

Highly sensitive catalytic determination of molybdenum.

A novel, highly sensitive, selective, and simple kinetic method was developed for the determination of Mo(VI) based on its catalytic effect on the oxidation of 1-amino-2-naphthol-4-sulfonic acid (ANSA) with H(2)O(2). The reaction was followed spectrophotometrically by tracing the oxidized product at 465nm after 30min of mixing the reagents. The optimum reaction conditions were: 10mmol l(-1) ANSA, 50mmol l(-1) H(2)O(2), 100mmol l(-1) acetate buffer of pH 5.0+/-0.05 and at 40 degrees C. Addition of 200microg ml(-1) diethylenetriaminepentaacetic acid (DTPA) conferred high selectivity for the proposed method. Following the recommended procedure, Mo(VI) could be determined with a linear calibration graph up to 2.5ng ml(-1) and a detection limit, based on the 3S(b)-criterion, of 0.027ng ml(-1). The unique sensitivity and selectivity of the implemented method allowed its direct application to the determination of Mo(VI) in natural and industrial waste water. The method was validated by comparison with the standard ETAAS method. Moreover, published catalytic-spectrophotometric methods for the determination of molybdenum were reviewed.

Catalytic spectrophotometric determination of hexavalent chromium

A simple, highly selective and sensitive catalytic method is presented for the determination of CrVI in natural and highly polluted waste-waters. The method is based on the catalytic effect of CrVI on the oxidation of 2-aminophenol (AP) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 430 nm after 10 minutes of mixing the reagents. The optimum reaction conditions are 2 × 10−3 mol l−1 of AP, 0.3 mol l−1 of H2O2 and 2.5 × 10−2 mol l−1 of phosphate buffer (pH 6.45 ± 0.02), at 40°C. The linear range of the calibration graph was up to 7.0 ng ml−1 of CrVI and the detection limit (3Sb) was 0.10 ng ml−1. Interferences of CrIII and FeIII ions were eliminated by a quantitative co-precipitation with Al(OH)3, rendering the method highly selective for CrVI. Spectrophotometric determination of as little as 1.0 ng ml−1 of CrVI in aqueous solutions gave an average recovery of 99.5% with a relative standard deviation of 1.2% (n = 5). The implemented method was conveniently applied to natural and highly polluted industrial waste waters. A comparison of published catalytic-spectrophotometric methods is also presented.

KINETIC DETERMINATION OF VANADIUM USING THE BROMATE OXIDATIVE COUPLING REACTION OF 4-(METHYLAMINO)PHENOL WITH 2,3,4-TRIHYDROXYBENZOIC ACID AND TARTRATE ACTIVATOR

ABSTRACT A new, simple, sensitive and selective kinetic method is developed for the spectrophotometric determination of VV and/or VIV based on its catalytic effect on the bromate oxidative coupling reaction of 4-(methylamino)phenol (MAP) with 2,3,4-trihydroxybenzoic acid (THBA) in the presence of tartrate as an activator. The reagents: 6.4 mmol l−1 MAP, 2.0 mmol l−1 THBA and 160 mmol l−1 bromate were mixed in the presence of an activator-buffer solution of 10 mmol l−1 tartrate (pH = 3.10) and at 35°C. The rate of formation of the oxidative coupling product was followed at 380 and/or 570 nm for 3 min from the addition of bromate. Linear calibration graphs up to 0.75 ng ml−1 of vanadium were obtained with detection limits, based on the 3S b criterion, of 0.019 and 0.026 ng ml−1 at 380 and 570 nm, respectively. The developed method was conveniently applied to the determination of vanadium in tap and ground waters and in human plasma, serum, and urine. Moreover, the nature of the oxidative coupling product was inferred and the kinetics and mechanism of the activating effects of tartrate were elucidated.

Sensitive determination of nitrite using its catalytic effect on the bromate oxidation of prochlorperazine

A highly sensitive and selective catalytic method is described for the determination of trace amounts of nitrite based on its effect on the oxidation of prochlorperazine (PCP) with bromate. The reaction rate was monitored spectrophotometrically by following the formation of the red oxidation product of PCP at 525 nm, within 1 min of mixing the reagents. The optimum reaction conditions were 40 µmol l–1 PCP, 0.20 mol l–1 H3PO4 and 10 mmol l–1 bromate at 25 °C. A 1 mmol l–1 EDTA concentration and 2 µmol l–1 HgII were used as effective masking agents for vanadium and iodide ions, respectively. By using the recommended procedure, the calibration graph was linear up to 70 ng ml–1 of nitrite; the detection limit was 0.8 ng ml–1. The method was applied to the determination of nitrite in rain and polluted river waters.

Catalytic determination of iodide using the promethazine–hydrogen peroxide redox reaction

A highly selective and sensitive spectrophotometric method was developed for the determination of iodide based on its catalytic effect on the oxidation of promethazine hydrochloride (PM) with H2O2. The red oxidation product of PM is monitored at 516 nm for 40 s. Using the recommended procedure, iodide can be determined with a linear calibration graph up to 12 ng ml–1 at 25 °C. The limit of detection is about 0.1 ng ml–1. The mechanism of the reaction is inferred. The method was successfully applied to the determination of iodide in river waters.

Molecular imprinted chitosan-TiO2 nanocomposite for the selective removal of Rose Bengal from wastewater

A new molecularly imprinted polymer (MIP) chitosan-TiO2 nanocomposite (CTNC) was prepared for the selective and quantitative removal of Rose Bengal dye from industrial wastewater. The physicochemical features of the prepared CTNC-MIP nanoparticles were thoroughly investigated. The prepared MIP nanoparticles exhibited high surface area (95.38m2/g) with relatively uniform mesoporous channels that allowed an exceptional uptake of the dye (qm=79.365mg/g) and reflected the high selectivity of the prepared MIP compared to pure chitosan. The dye uptake was investigated using Freundlich, Langmuir, Dubinin Radushkevich and Temkin models. The kinetics of removal was explored by pseudo-first, pseudo second order, Elovich and Weber-Morris models. The Experimental data fitted well into pseudo-second order model, and much well with the Langmuir isotherm confirming the formation of monolayer of dye molecules. The enthalpy of adsorption was (62.279kJmol-1) showing strong interaction of MIP with the dye. The prepared MIP exhibited a good recyclability and stability.

Digital imaging devices as sensors for iron determination

Portable, sensitive and cost-effective sensors represent an unmet need, especially in resource-limited settings and locally deprived communities. Digital imaging devices can fill the gap. Thus, we have tested a desktop scanner, a digital camera and a smartphone to determine iron using three standard colour reactions. Images of reacting solutions were analysed to obtain the RGB (red, green and blue) non-uniform colour space parameters. To improve the calibration linearity, sensitivity, and detection limit, we converted the RGB intensities into six uniform colour space values and two colour differences attributes. The converted signals surpassed the RGB signals and compared well with reference spectrophotometric signals. The simplicity and sensitivity of this approach make digital imaging devices as excellent competitors to field-monitoring instruments and sophisticated spectrophotometers. Our approach was successfully applied to the assessment of iron in Nile river water, soils, plant materials and meat and liver samples.