[Show abstract][Hide abstract] ABSTRACT: Bread loaves randomly sampled from nine outlets and bakeries within Ile-Ife wereanalysed to determine their safety levels for human consumption with respect to bromate and trace metal contents. Bromate determinationwas carried out via spectrophotometric method while trace metals in the digested bread samples were profiledusing Flame Atomic Absorption Spectrophotometer. Bromate levels in the analyzed bread samples ranged from 2.051 ± 0.011 μg/g to 66.224 ± 0.014 μg/g while the tracemetal levels were of the order: 0.03-0.10 μg/g Co = 0.03-0.10 μg/g Pb< 0.23-0.46 μg/gCu <2.23-6.63 μg/g Zn < 25.83-75.53 μg/g Mn.This study revealed that many bread bakers around Ile-Ife had not fully complied with the bromate-free rule stipulated by NAFDAC contrary to the “bromate free” inscribed on the labels of the bread. The bread samples containedboth essential and toxic trace metals to levels that could threaten the health of consumers over prolonged regular consumption.
[Show abstract][Hide abstract] ABSTRACT: This work assessed levels of heavy metals exposure from silver coatings of mobile phones recharge cards of three major companies (designated as A, B and C) with price denominations 100, 200 and 400 from companies A, B and C respectively, which were carefully scratched using a plastic scraper into a glass tube. The coatings were acid digested for total metal concentration, while speciation experiment for Mn, Cu, Cd and Pb was carried out. Total metals and speciation analysis were done using AAS and XRF techniques. The total metal concentration from XRF analysis was in the range: Ca (70-2140 μg/g), K (20–4930 μg/g), Sc (80–270 μg/g), Ti (1530–12580 μg/g), Fe (50–6660 μg/g), Ni (20–2040 μg/g), Cu (20 - 850 μg/g) and Zn (40–460 μg/g). Cr had the lowest concentration (10 μg/g) in A ( 400) while Ti had the highest concentration (12580 μg/g) in C ( 500) for all the coatings analyzed. AAS and XRF results agreed closely except for Fe with higher concentration. A ( 100) contained high concentration of the metals compared with others. Speciation study identified Mn as the most mobile element when present in the environment.
[Show abstract][Hide abstract] ABSTRACT: The determination of heavy metals in consumer products is crucial for the safety appraisal and sources classification of human and environmental exposures. These products contain various undisclosed chemical constituents with no or little known health safety information. The public is generally unaware of these types of everyday exposure from chemical constituents of consumer products and their health consequences. In this study, we recorded a body of proof demonstrating potential harm of consumer goods, by determining concentrations of total cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), iron (Fe), lead (Pb) and nikel (Ni contents in a variety of personal care products (n = 82) commonly used in Nigeria, using flame atomic absorption spectrometer after dry and wet digestion methods. The results of the analysis indicated that the range of Cd was 0.035 ± 0.023–0.467 ± 0.167 ppm, Cr 0.015 ± 0.009–0.435 ± 0.232 ppm, Cu 0.230 ± 0.08–0.603 ± 0.025 ppm, Zn 0.003 ± 0.005–0.743 ± 0.066 ppm, Fe 0.233 ± 0.219–1.401 ± 1.878 ppm, Pb 0.02 ± 0.007–0.2050.129 ppm and Ni 0.035 ± 0.015–0.093 ± 0.06 ppm. The values of Cd and Cr are a cause for alarm because the elements are not allowed in any amount in cosmetics. Despite the fact that zinc is essential in the body, the values obtained in this study deserves safety concerns due to cumulative effect, arising from incessant exposure.
[Show abstract][Hide abstract] ABSTRACT: The effects of various degumming agents on the trace metal concentrations of five nonconventional oils extracted from the seeds of Terminalia catappa, Irvingia gabonensis, Persea americana, Dacryodes edulis and fleshy mesocarp of D. edulis fruit and one conventional oil extracted from Glycine max were studied. The degumming of these oils was done using distilled water, NaCl solution and Ca–Mg salt solution at various concentrations as degumming agents. The findings showed that the degumming ability of the various degumming agents varied from one oil to another, with the degumming efficiency of 100–300 µg/mL NaCl solutions higher than that of 50–250 µg/mL Mg–Ca solutions. For the developing countries, the degumming process outlined in this study is a viable and an affordable alternative to the hi‐tech procedures available in the developed countries. PRACTICAL APPLICATIONSIrvingia gabonensis, Terminalia catappa, Dacryodes edulis and Persea americana are local plants cultivated across Nigeria. Their seeds and fruits have found applications in both human and animal feeding because of their high oil and protein content. However, these nonconventional oil seed sources are prone to chemical rancidity and poor shelf life because of lack of adequate technology in handling and preserving their fruits, seeds and oils. The main application of this study is to come up with cheap technology and efficient process of removing some of the chemical components of the oils responsible for their low shelf life. This could assist the food industries in the developing countries to solve the problems of the high cost of and unavailable technology from the developed nations, and hence, tackle the problem of oil spoilage or rancidity using the findings of this research.
Journal of Food Processing and Preservation 01/2013; 37(5). · 0.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H2SO4) and sodium sulphate (Na2SO4) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF cm−2 (ca 2,119 F g−1) in H2SO4. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.
Journal of Solid State Electrochemistry 01/2013; 17(5). · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Edged plane pyrolytic graphite electrode (EPPGE) was modified with and without Prussian blue (PB) nanoparticles and polyaminobenzene sulphonated single-walled carbon nanotubes (SWCNTPABS) using the chemical deposition method. The electrodes were characterised using microscopy, spectroscopy and electrochemical techniques. Results showed that edged plane pyrolytic graphite-single-walled carbon nanotubes-prussian blue (EPPGE-SWCNT-PB) electrode gave the best dopamine (DA) current response, which increases with increasing PB layers. The catalytic rate constant of 1.69 × 10(5)mol(-1)cm(3)s(-1), Tafel value of 112 mV dec(-1), and limit of detection of DA (2.8 nM) were obtained. Dopamine could be simultaneously detected with ascorbic acid. The electrode was found to be electrochemically stable, reusable and can be used for the analysis of DA in real drug samples.
[Show abstract][Hide abstract] ABSTRACT: The electrochemical oxidation of phenol (Ph), 4-chlorophenol (4-ClPh) and 4-nitrophenol (4-NPh) at a platinum electrode modified with and without multi-walled carbon nanotubes/Prussian blue nanocomposite in a pH 7.0 phosphate buffer electrolyte was investigated by cyclic voltammetry (CV) and impedance measurements. The modified electrodes were characterised using techniques such as transmission electron microscopy (TEM), electron X-ray dispersive spectroscopy (XRD), cyclic voltammetry (CVs) and electrochemical impedance spectroscopy (EIS). The phenol produced an irreversible CV oxidation peak whose potential increased for 4-ClPh and 4-NPh derivatives. Pt-MWCNT-SO3--PB electrode gave the highest electro-oxidation current compared to the other electrodes studied. The oxidation of the phenol compounds was not completely diffusion controlled especially at higher scan rate, and the electrode was characterized by some level of adsorption. The degree of adsorption was depicted by the Tafel values of 4292.4, 663.2 and 203.8 mVdec-1 for Ph, 4-ClPh and 4-NPh respectively. The limits of detection were in the micro molar range and the Gibbs free energy change (Go) due to adsorption was estimated as -33.8, -35.8 and -36.0 kJmol-1 for Ph, 4-ClPh and 4-NPh. Impedance data showed that the MWCNT-SO3--PB film was so porous and behaved as a pseudocapacitor towards the oxidation of the analytes.
International journal of electrochemical science 01/2012; 7. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Supercapacitive properties of Single-walled carbon nanotubes/metal oxides nanocomposites (SWCNT-MO where M=Ni, Fe, Co) have been described. The SWCNT-MO nanocomposites was confirmed with SEM, EDX and XPS techniques. Supercapacitive properties of the modified electrodes in H2SO4 and Na2SO4 electrolytes was investigated using cyclic voltammetry (CV), galvanostatic constant current charge-discharge (CD) and the electrochemical impedance spectroscopy (EIS) techniques. SWCNT-NiO nanocomposite modified electrodes gave better supercapacitive performance with a specific capacitance of 186 mF cm−2 (or 928 F g−1). This value compared quite favourably and even higher than values hitherto reported in several literature.
[Show abstract][Hide abstract] ABSTRACT: A Platinum (Pt) electrode was modified with gold and gold oxide nanoparticles electrodeposited on multi-walled carbon nanotubes. The modified electrodes were characterised with techniques such as Transmission Emission Microscopy (TEM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDX). The electrochemical properties were investigated using cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy. The electrodes were used as analytical probes towards the detection of dopamine (DA) and epinephrine (EP). Results showed that Pt-MWCNT-Au electrode gave the best dopamine and epinephrine current response at lower charge transfer resistance R ct values of 9.1 and 9.4 Ωcm 2 in DA and EP respectively compared with other electrodes. The electrooxidation of the analyte involved adsorbed intermediates with adsorptive capacitance (C ads) and Tafel values of, 331.6 µFcm -2 , 136.4 mVdec -1 in DA; and 225.2 µFcm -2 , 162.8 mVdec -1 in EP. The limit of detection were 78±6.5 nM and 350±28.4 nM while the catalytic rate constant (K) were (13.8±2.4) and (18.9±4.2) x 10 8 cm 3 mol -1 s -1 for DA and EP respectively on the electrode. The limit of detection is favourable for DA detection in biological system where DA exists in µM concentration. The electrode was easy to prepare and was also electrochemically stable such that it could be used for the detection of DA and EP in the presence of interfering species such as ascorbic acid (AA).
Int. J. Electrochem. Sci. International Journal. 01/2011; 6:2826-2844.
[Show abstract][Hide abstract] ABSTRACT: Supercapacitive properties of synthesised nickel oxides (NiO) nanoparticles integrated with multi-walled carbon nanotubes (MWCNT) in a two-electrode coin cell type supercapacitor were investigated. Successful formation of the MWCNT-NiO nanocomposite was confirmed with techniques such as transmission electron microscopy (TEM), scan electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDX) and X-ray diffraction spectroscopy (XRD). The supercapacitance behaviour of both the symmetry and the asymmetry MWCNT-NiO based supercapacitor in 1 M H 2 SO 4 and 1 M Na 2 SO 4 electrolytes was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic constant current charge-discharge (CD) techniques. There was a good correlation between the CV and the CD specific capacitance (SC) values for the asymmetry supercapacitor. Asymmetry supercapacitor (MWCNT-NiO|H 2 SO 4 |MWCNT) gave the highest SC value of 925.9 mFcm -2 (53.9 F g -1). High SC values which are higher than most of those reported in literature were obtained. The electrodes demonstrated high stabilities with no significant changes in SC values over 1000 cycles.
International journal of electrochemical science 01/2011; 6:4760-4774. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nitrite, NO 2 -(in neutral), and NO (in acidic media) were used as analytical probe to investigate the electrocatalytic properties of Prussian blue nanoparticles (PB) modified edge plane pyrolytic graphite (EPPG) electrode. Results indicate that single-walled carbon nanotubes-Prussian blue hybrid (SWCNT-PB) modified electrode demonstrated greater sensitivity and catalysis towards nitrite compared to PB or a SWCNT modified electrode. The current response of the electrode was reduced in the presence of cetyltrimethylammoniumbromide (CTAB) which was used as a stabilising agent. Electrocatalytic oxidation of nitrite occurred through a simple adsorption controlled electrode reaction. The adsorption equilibrium constant β and the standard free energy change ΔG 0 due to adsorption were 4.35 x 10 3 M -1 s -1 (-20.76 kJmol -1) and 15.0 x 10 4 M -1 s -1 (-29.53 kJmol -1) for nitrite and nitric oxide respectively. Despite the adsorption, the EPPGE-SWCNT-PB electrode showed good stability of greater than 80% in the analytes. The electrode's limit of detection and catalytic rate constant were 6.26 µM (4.37 x 10 6 cm 3 mol -1 s -1) and 4.9 µM (6.35 x 10 5 cm 3 mol -1 s -1) for nitrite and nitric oxide respectively. The fabricated electrode is not difficult to prepare and could serve as a potential sensor for nitrite determination in food and environmental samples.
International journal of electrochemical science 01/2011; 6:4388-4403. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, edged plane pyrolytic graphite electrode EPPGE was modified with functionalised single-walled carbon nanotubes and Prussian blue nanoparticles (PB). The modified electrode was characterised by techniques such as TEM, FTIR, XPS, EDX and cyclic voltammetry. The EPPGE-SWCNT-PB platform exhibited enhanced electron transport and catalytic efficiency towards the oxidation of Diethylaminoethanethiol (DEAET) and hydrazine compared with the other electrodes studied. The EPPGE-SWCNT-PB showed good electrochemical stability in the analytical solution, showing limit of detection in the micromolar range and catalytic rate constant of 3.71×106 and 7.56×106 cm3 mol−1 s−1 for DEAET and hydrazine respectively. The adsorption properties of these analytes that impact on their detection at the SWCNT-PB film modified electrode were evaluated and discussed.
[Show abstract][Hide abstract] ABSTRACT: The electrochemical decoration of edge plane pyrolytic graphite electrode (EPPGE) with cobalt and cobalt oxide nanoparticles integrated with and without single-walled carbon nanotubes (SWCNTs) is described. Successful modification of the electrodes was confirmed by field emission scanning electron microscopy (FESEM), AFM and EDX techniques. The electron transfer behaviour of the modified electrodes was investigated in [Fe(CN)6]3−/4− redox probe using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and discussed. The study showed that cobalt nanoparticles modified electrodes exhibit faster electron transfer behaviour than their oxides. The catalytic rate constant (K) obtained at the EPPGE–SWCNT–Co for nitrite at pH 7.4 and 3.0 are approximately the same (∼3 × 104 cm3 mol−1 s−1) while the limits of detection (LoD = 3.3δ/m) are in the μM order. From the adsorption stripping voltammetry, the electrochemical adsorption equilibrium constant β was estimated as (13.0 ± 0.1) × 103 M−1 at pH 7.4 and (56.7 ± 0.1) × 103 M−1 at pH 3.0 while the free energy change (ΔG°) due to the adsorption was estimated as −6.36 and −10.00 kJ mol−1 for nitrite at pH 7.4 and 3.0, respectively.
[Show abstract][Hide abstract] ABSTRACT: Electrochemical sensors using edge-plane pyrolytic graphite electrode (EPPGEs) modified with single-wall carbon nanotubes–iron (III) oxide (SWCNT/Fe2O3) nanoparticles for the sensitive detection of dopamine (DA) are described for the first time. The surface of the EPPGE-SWCNT–Fe2O3 was characterized using field emission scanning electron microscopy, atomic force microscopy and energy dispersive X-ray spectroscopy while the electrochemical properties were investigated using the cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy techniques. When compared with the bare electrode or electrodes without the Fe2O3 nanoparticles, the EPPGE-SWCNT–Fe2O3 gave best response (7 times more than bare EPPGE and 2-fold more than the other two modified electrodes) towards the detection of DA. Also, the EPPGE-SWCNT–Fe2O3 showed the best analytical performance for DA with an electron transfer rate constant of ∼0.26 cm s−1, a sensitivity of 3.44 μA μM−1, a limit of detection of 0.36 μM, a catalytic rate constant of 8.7 × 105 cm3 mol−1 s−1, and a diffusion coefficient of 3.5 × 10−5 cm2 s−1. This electrode can be reliably used to assay DA in its real drug composition.
[Show abstract][Hide abstract] ABSTRACT: This work describes the electron transport and electrocatalytic properties of chemically-synthesized nickel (Ni) and nickel oxide (NiO) nanoparticles supported on multi-walled carbon nanotubes (MWCNT) platforms. Successful modification of the electrodes with the Ni and NiO nanoparticles was confirmed by techniques such as FTIR, FESEM, HRSEM, TEM, XRD, EDX and cyclic voltammetry (CV). The electrocatalytic oxidation of DEAET and hydrazine on the modified electrodes was investigated using CV and electrochemical impedance spectroscopy (EIS) and discussed. Results showed that EPPGE–MWCNT–Ni electrode gave the best electro-oxidation response towards DEAET and hydrazine. The catalytic rate constant and the limit of detection of the electrode to DEAET and hydrazine were 5.93 × 109 cm3 mol−1 s−1 (0.87 μM) and 7.67 × 108 cm3 mol−1 s−1 (0.29 μM), respectively. The electrochemical Gibbs free energy change due to adsorption (ΔG0) for the EPPGE–MWCNT–Ni in DEAET and hydrazine were estimated as −18.14 and −17.21 kJ mol−1, respectively. The electrode has proven to be a potential electrochemical sensor for DEAET and hydrazine.
[Show abstract][Hide abstract] ABSTRACT: Numerous studies have described human exposure to heavy metals from diverse sources in Nigeria, but little is known about the exposure from personal care products, and few or no report is available on the personal care product concentrations of cadmium, chromium, copper and zinc, which have biotic effects. The levels of these elements were determined in 74 samples of 5 different classes of personal care products commonly used in Nigeria using atomic absorption spectrophotometry. Significant levels of Cd, Cr, Cu and Zn were found in all the products. The highest values of Cd (0.553 ppm) and Cu (0.783 ppm) were observed in hair cream, while medicated cream was mostly implicated for Cr (0.383 ppm) and Zn (0.793 ppm). Since no limit relating to cosmetic products is available, it is difficult to ascertain if the values of metals obtained in this study are too high or low; but Cd and Cr are prohibited in any amount in cosmetics. Prolonged use of soaps and creams containing these elements may pose threat to human health and the environment.
Bulletin of Environmental Contamination and Toxicology 09/2009; 84(1):8-14. · 1.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electrocatalytic behavior of diethylaminoethanethiol (DEAET) at nickel nanoparticle-electrodecorated single-walled carbon nanotube (SWCNT-Ni) platform is presented. We demonstrate that the electrocatalytic response is governed by adsorption-controlled kinetics and that adsorptive stripping voltammetry (AdsSV) represents a viable analytical voltammetry for the sensitive detection of this hydrolysis product of a V-type nerve agent.
[Show abstract][Hide abstract] ABSTRACT: The electron transfer behaviour of nickel film-decorated single-walled carbon nanotubes (SWCNTs-Ni) at edge plane pyrolytic graphite electrodes (EPPGEs) was investigated. The impact of SWCNTs on the redox properties of the nickel film was investigated with cyclic voltammetry and electrochemical impedance spectroscopy (EIS). From EIS data, obtained using ferrocyanide/ferricyanide as a redox probe, we show that the electrodes based on nickel and nickel oxide films follow electrical equivalent circuit models typical of partial charge transfer or adsorption-controlled kinetics, resembling the “electrolyte–insulator–semiconductor sensors (EIS)”. From the models, we prove that EPPGE-SWCNT-Ni exhibits the least resistance to charge transport compared to other electrodes (approximately 30 times faster than the EPPGE-SWCNT-NiO, 25 times faster than EPPGE-SWCNT, and over 300 times faster than the bare EPPGE) suggesting the ability of the SWCNTs to act as efficient conducting species that facilitate electron transport of the integrated nickel and nickel oxide particles.
[Show abstract][Hide abstract] ABSTRACT: Runoff was collected from three different roofing materials that are commonly used for roofing in Ile-Ife, Nigeria, between the months of June to August, 2004. The samples were collected in four geographical locations in the town. The run offs were analysed for pH, Temp, TDS, CI- , S042-, PO43-, N032-, EC and some heavy metals both as regards total, dissolved and particulate fractions. Analysis of the heavy metals was done using flame Atomic Absorption Spectrophotometer. The quantity of these parameters varies with the different roofing materials. In terms of dissolved metals, Fe is the most predominant metal with mean values 0.59 ± 0.29, 0.82 ± 0.14, and 1.04 ± 0.27 mg/L for asbestos, ceramic tiles and metal sheets respectively. The tendency of the roofing materials to release dissolved metals is arranged as follows: Zn, Cr and Fe (metal sheet > Ceramic > asbestos); Cd and Pb (asbestos > ceramic > metal sheet). In terms of particulate metals, the concentration of Cd and Pb are higher in the asbestos than other roofing stuffs. The sequence of their predominance in asbestos is as follows: Pb (0.830.55 mg/L) > Cd (0.29 0.07 mg/L). In all the roofs, both particulate and dissolved metals except Zn exceeded WHO permissible limits for drinking water. The high levels of the metals obtained in this study may likely result in consumer complaints since some of the metals are not only carcinogenic but are also liable of impacting bad taste in water.
International Journal of Environmental Science and Technology. 01/2006;
[Show abstract][Hide abstract] ABSTRACT: Electrochemistry of edge-plane pyrolytic graphite electrodes (EPPGEs) modified with Aldrich single-walled carbon nanotubes
(SWCNTs) electro-decorated with metal (Ni, Fe and Co) and their oxides have been studied. The morphology and identity of the
metallic dispersions were examined by scanning electron microscopy and energy-dispersive spectroscopy. We show that SWCNTs
serve as efficient conducting carbon material for electronic communication between metal films and the underlying carbon electrode.
By using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques, it is proved that both EPPGE-SWCNT-Ni
and EPPGE-SWCNT-Fe exhibit comparable electrochemical response in buffered aqueous solution (pH 7.0) and towards electro-oxidation
of hydrazine in Na2SO4 solution. The impedance spectra of these SWCNT-metal hybrids were complicated and follow electrical equivalent circuit model
typical of adsorption-controlled charge transfer kinetics. Hydrazine impedance spectra exhibited inductive loop, characteristic
of Faradaic current being governed by the occupation of an intermediate state. On the other hand, the EIS data obtained in
a simple redox probe, [Fe(CN)6]3−/[Fe(CN)6]4−, showed that EPPGE-SWCNT and EPPGE-SWCNT-Ni followed electrical equivalent circuit models typical of partial charge transfer
or adsorption-controlled kinetics with some resemblance to the behaviour of electrolyte–insulator–semiconductor sensors.
Journal of Solid State Electrochemistry 12(10):1325-1336. · 2.28 Impact Factor