J. Catherine Ngila

Preconcentration of molybdenum, antimony and vanadium in gasolsine samples using Dowex 1-x8 resin and their determination with inductively coupled plasma-optical emission spectrometry.

Strong ion exchangers (Dowex 50W-x8 and Dowex 1-x8) were used for the separation and preconcentration of trace amounts of Mo, Sb and V in gasoline samples. Dowex 1-x8 resin was found to be suitable for the quantitative retention of these metal ions from organic matrices. The elution of the metal ions from Dowex 1-x8 resin was achieved by using 2.0 mol L(-1) HNO3 solution. The Dowex 1-x8 preconcentration and separation method gave an enrichment factor of 120 with limits of detection equal to 0.14, 0.05 and 0.03 μg L(-1) for Mo, Sb and V, respectively. The limits of quantification were found to be 0.48, 0.18 and 0.10 μg L(-1) for Mo, Sb and V, respectively. Under optimized conditions, the relative standard deviations of the proposed method (n=20) were <4%. The accuracy of Dowex 1-x8 preconcentration procedure was verified by the recovery test in the spiked samples of gasoline sample. The Dowex 1-x8 preconcentration method was applied to Conostan custom made oil based certified reference material for the determination of Mo, Sb and V. The results of the paired t-test at a 95% confidence level showed no significant difference. The separation and preconcentration procedure was also applied to the gasoline samples collected from different filling stations.

Functionalized nanometer-sized alumina supported micro-solid phase extraction coupled to inductively coupled plasma mass spectrometry for preconcentration and determination of trace metal ions in gasoline samples

Nanometer-sized alumina functionalized with [3-(2-aminoethylamino) propyl] trimethoxysilane (nano-Al2O3/AAPTMS) was prepared as an adsorbent for preconcentration of trace element ions in gasoline samples. The nano-Al2O3 was characterized by XRD, SEM and BET techniques and the functionalized adsorbent was characterized by ATR-FTIR spectroscopy. The nano-Al2O3/AAPTMS sorbent was used as the packing material in the supported micro-solid-phase extraction (μ-SPE) device. The latter was coupled with inductively coupled plasma mass spectrometry (ICP-MS) for preconcentration and determination of trace elements in gasoline samples. The optimization of the preconcentration system was achieved by a multivariate strategy. Under optimized conditions, limits of detection (LOD) and quantification (LOQ) ranged from 0.2–0.7 ng L−1 to 0.7–2.3 ng L−1, respectively, and a preconcentration factor of 40 was achieved. The validity of the developed μ-SPE-ICP-MS procedure was confirmed by analysis of spiked gasoline samples. The supported μ-SPE-ICP-MS method was applied for quantification of Co, Cr, Mn, Ni and Ti in commercial gasoline samples. The μSPE device coupled with ICP-MS provided improved LOD and LOQ for trace metal analysis in a gasoline matrix and significantly reduced matrix interference.

A single-step microwave-assisted acid extraction of total sulphur in coal samples followed by ICP-OES determination

A rapid microwave-assisted acid extraction (MW-AAE) procedure using a dilute [HNO3–H2O2] mixture followed by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis has been developed for the determination of total sulphur in coal samples. Parameters affecting the MW-AAE such as extractant concentration, microwave temperature, extraction time, coal amount and HNO3 : H2O2 volume ratio were optimized by using a certified reference material (SARM 20) in order to attain total sulphur quantitative recoveries. The optimum conditions for the extraction procedure were found to be 180 °C, 5 min, 3 mol L−1, 3 mol L−1, 0.05 g and 2 : 1 for microwave temperature, extraction time, [HNO3], [H2O2], coal amount and HNO3 : H2O2 volume ratio, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analyzing three coal certified reference materials (SARM 18, 19 and 20) and quantitative recoveries (83–102%) were achieved. Additionally, the precision of the proposed method, expressed in terms of relative standard deviation (n = 15), was satisfactory (≤3%). The method limit of detection (0.026 μg g−1) and method limit of quantification (0.087 μg g−1) for sulphur analysis were relatively good as compared to work reported in the literature.

Pre-concentration of trace elements in short chain alcohols using different commercial cation exchange resins prior to inductively coupled plasma-optical emission spectrometric detection.

Chelex-100, Dowex 50W-x8 and Dowex MAC-3 exchange resins were investigated for separation and pre-concentration of trace amounts of Cd, Cr, Cu, Fe, Mn, Pb, Ti and Zn in alcohols with respect to retention and desorption characteristics. Dowex 50W-x8 was found to be the best sorbent with percentages recoveries >95%. In addition, Chelex-100 appeared to be suitable for the pre-concentration of Cu, Fe and Zn, whereas Dowex MAC-3 was selective for Cu and Fe. Therefore, Dowex 50W-x8 was used for further investigations. The relative standard deviations <4% (n=20), limits of detection and quantification were 0.1-1.2 μg L(-1) and 0.3-1.5 μg L(-1), respectively. The SPE method was validated against a certified reference material and the results were in agreement with certified values. The accuracy of the optimized method was verified by the recovery test in the spiked alcohol samples. The accuracy and spike recovery test for different metal ions were in the range 98-102% and 95-105%, respectively. The optimized method was applied to the separation and pre-concentration of metal ions in different commercial alcohol samples.

Development of a novel and green microwave-assisted hydrogen peroxide digestion method for total sulphur quantitative extraction in coal samples prior to inductively coupled plasma-optical emission spectroscopy and ion-chromatography determination

A green, novel, fast and cost effective procedure has been developed for determination of total sulphur in coal samples based on the use of diluted hydrogen peroxide and microwave irradiation. The resulting digests were then analysed by using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and ion-chromatography (IC). The investigated factors include hydrogen peroxide concentration, microwave temperature, extraction time and coal amount. A certified reference material (SARM 20) was used for the optimization of the influential experimental parameter. It was observed that quantitative recoveries of total sulphur in coal could be attained when microwave temperature, extraction time, [H2O2], and coal amount are 150 °C, 5 min, 3 mol L−1 and 0.05 g, respectively. In addition, the 24 factorial design results demonstrated that the interactions between coal amount and time (BD) as well as coal amount and temperature (BC) were significant at a 95% confidence level. Under optimum conditions, the accuracy of the proposed microwave-assisted hydrogen peroxide digestion (MW-AHPD) method was examined by analysing three coal certified reference materials (SARM 18, 19 and 20) and quantitative recoveries (89–101%) were achieved. Additionally, the precision of the proposed method, expressed in terms of relative standard deviation (n = 15), was satisfactory (≤1.5%). The method detection limit (0.014 μg g−1) and method quantification limit (0.047 μg g−1) for sulphur analysis were relatively good compared to those reported in the literature. The proposed digestion method converted all the sulphur species into sulphates as confirmed by the IC results and it can be routinely applied to replace the standard Eschka method. The P-XRD results confirmed the undigested kaolinite and quartz minerals.

A rapid microwave-assisted acid extraction method based on the use of diluted HNO3-H2O2 followed by ICP-MS analysis for simultaneous determination of trace elements in coal samples

Before coal processing such as pyrolysis, liquefaction, gasification and combustion, it is very crucial to monitor the trace element concentration levels as that determines the coal quality. Therefore, the current study describes the development of microwave-assisted acid extraction (MW-AAE) method for extraction of 15 trace elements in coal samples prior to their determination using inductively coupled plasma-mass spectrometry. Diluted HNO3-H2O2 was used in order to reduce reagents amount used, eliminate matrix interferences caused by concentrated acids and to decrease waste produced in analytical laboratories. The optimisation of the proposed extraction method was carried out by using a full factorial design (24) involving four factors; that is, temperature, extraction time, HNO3 and H2O2 concentrations. The optimum conditions for the MW-AAE procedure were found to be 200°C, 5 min, 5 mol L−1 and 2 mol L−1 for temperature, extraction time, HNO3 and H2O2 concentrations, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analysing three coal certified reference materials (SARM 18, 19 and 20) and recoveries of 80–115% were achieved for V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Zr, Cs, Ba, Pb and U, except for Ti (10–25%) and Hf (27–70%). In addition, the precision of the proposed method, expressed in terms of relative standard deviation (SD) (n = 15), was within the accepted range (≤3.5%). The method detection limits of 0.001–0.57 µg g−1 for all trace elements under the investigation were similar to the literature reported work, except for Ti (4.00 µg g−1).

Alumina–titania (Al2O3–TiO2) hollow fiber sorptive microextraction coupled to inductively coupled plasma mass spectrometry for determination of trace elements in diesel and gasoline samples

An alumina–titania (Al2O3–TiO2) hollow fiber membrane was synthesized using the template method coupled with a sol–gel process. The crystal forms of the mixed oxide hollow fiber was evaluated using X-ray diffraction (XRD). The morphological structure and surface characteristics of the Al2O3–TiO2 hollow fiber were characterized by scanning electron microscopy (SEM) and nitrogen adsorption/desorption BET techniques. The synthesized Al2O3–TiO2 hollow fiber membrane was combined with inductively coupled plasma mass spectrometry for on-line preconcentration and determination of trace amounts of Co, Cr, Mo, Ni, Sb and V in diesel and gasoline samples. The optimization of the experimental parameters affecting the preconcentration and determination of target analytes was performed using a full 24 factorial and central composite designs. Under optimized conditions, limits of detection (LOD) (based on the original sample) and limits of quantification (LOQ) ranged 0.1–0.9 and 0.3–3.0 ng L−1, respectively. The developed method was applied in the determination of trace elements in real diesel and gasoline samples.

Kinetics and Equilibrium Studies for the Removal of Cobalt, Manganese, and Silver in Ethanol using Dowex 50W-x8 Cation Exchange Resin

Organic solvents such as ethanol, find a wide range of applications in fuel, pharmaceutical industries, food industries, and paint formulations, among others. The removal of Ag(I), Co(II), and Mn(II) ions in ethanol by cation exchange resin, Dowex 50W-x8, was investigated. The adsorption characteristics of metal ions onto Dowex 50W-x8 resin were described by Langmuir isotherms. The maximum sorption exchange capacities at 298 K were obtained as 47.4 mg g−1, 52.6 mg g−1, and 58.5 mg g−1 for Ag(I), Co(II), and Mn(II), respectively. The data was also fitted to Temkin and Dubinin-Radushkevich adsorption isotherm models to evaluate other adsorption properties. The ion exchange of silver, cobalt, and manganese on cation exchange resin followed pseudo-second-order kinetics, and the intraparticle diffusion was rate-determining step. The thermodynamic parameters indicated that the sorption of metal ions onto Dowex 50W-x8 resin was spontaneous (negative ΔG°) and endothermic in nature (positive ΔH°) implying that the adsorption capacity increased with increasing temperature. The resin can be regenerated by eluting metal ions with 3.0 mol L−1 HNO3 followed by washing it with 10 mL of Millipore water and 10 mL of 2.0 M NaOH, respectively. The proposed method was applied for metal ion removal in real ethanol samples.

Application of waste tyre-based activated carbon for the removal of heavy metals in wastewater

Abstract This study presents the preparation and characterization of chemically activated carbonaceous materials obtained from waste tyres and the prepared adsorbent was applied for the adsorptive removal of Cd(II) and Pb(II) in the domestic wastewater samples. The activation efficiency of phosphoric acid (H3PO4) and hydrogen peroxide (H2O2) were evaluated and H2O2 was chosen as the appropriate activating agent as compared to phosphoric acid. The developed adsorbent was characterized using the scanning electron microscope (SEM), Brunnuer Emmet Teller (BET) which helped to decide which adsorbent material is best in terms of the surface area and Fourier transform infrared spectroscopy (FT-IR). Two-level fractional factorial design was used for the optimization of parameters affecting the adsorptive removal of Cd(II) and Pb(II). The optimum conditions were found to be 6.5, 0.2 g, 32.5 min and 55 mg L−1, for sample pH, mass of adsorbent, contact time and initial concentration, respectively. Amongst every adsorption isotherms that were used, Langmuir model was preferred due to the highest value of the correlation coefficient (r2). Therefore, the adsorption capacities of Cd(II) and Pb(II) were 201 and 196 mg g−1, respectively. The regeneration studies were performed and the adsorbent was capable of been used ten times and the material was stable with only a slight decrease in the removal efficiency of Cd(II) and Pb(II). Furthermore, the prepared adsorbent prepared was successfully applied for the removal of Cd(II) and Pb(II) in real environmental samples and the inductively coupled plasma optical emission spectroscopy was used for the analysis.

Indirect Amperometric Determination of Selected Heavy Metals Based on Horseradish Peroxidase Modified Electrodes

Due to the high toxicity of heavy metals, it is crucial to detect ultra low levels of the metals, especially in drinking water. The common techniques include spectrometric techniques such as inductively coupled plasmaatomic emission spectroscopy, ICP-AES (Bettinelli et al. 2000; Rahmi et al. 2007; Tuzen et al. 2008) as well as anodic stripping voltammetry (Brainina et al. 2004). Even though ICP techniques have low detection limits (ranges from parts per billion, ppb to parts per trillion, ppt (Berezhetskyy et al. 2008), however, they are unsuitable for in-situ analysis, they are expensive, sophisticated and require skilled operators. For these reasons, the development of alternative techniques such as electrochemical biosensor techniques, offer alternative methods because they are sensitive, low cost and simple to operate (Wang et al. 2009b). Recent developments have shown the use of electrochemical biosensors as indirect methods for detection of Cd2+, Cu2+, Cr3+, Zn2+, Ni2+ and Pb2+ using urease biosensor (Ilangovan et al. 2006; Tsai et al. 2003); Cd2+, Co2+, Zn2+, Ni2+ and Pb2+ using alkaline phosphatase (Berezhetskyy et al. 2008); Cd2+, Cu2+, Zn2+ and Pb2+ by glucose oxidase (Ghica and Brett 2008); Hg2+ using glucose oxidase invertase and mutarose (Mohammadi et al. 2005); Cu2+, Cd2+, Mn2+ and Fe3+ using acetylcholinesterase (Stoytcheva 2002); and Cu2+, Cd2+, Zn2+ and Pb2+ by nitrate reductase (Wang et al. 2009b). Horseradish peroxidase (HRP) biosensor has so far only been reported for detection of mercury (Han et al. 2001). This study sought to extend its application for detection of other metals such as lead, cadmium and copper. We have chosen cadmium due to its similarities with mercury with regards to toxicity as both metals, belong to the same group. In addition, we have also chosen copper and lead because of their common occurrence in environmental matrices (Pb from leaded petrol and Cu from wiring activities). Furthermore, copper is reported to show interaction with biological systems (Cecconi et al. 2002; Uriu-Adams and Keen 2005) and therefore interesting to see how it interacts with HRP enzyme. The main aim of this present work is to investigate the inhibition of HRP enzyme by Cd, Pb and Cu, a phenomenon that can be employed for their indirect determination. Kinetic studies were done to determine the nature of enzyme inhibition (whether it is reversible or irreversible and if reversible whether it is competitive or noncompetitive). The apparent