Philiswa N. Nomngongo

Fractionation of trace elements in agricultural soils using ultrasound assisted sequential extraction prior to inductively coupled plasma mass spectrometric determination.

The main objectives of this study were to determine the concentration of fourteen trace elements and to investigate their distribution as well as a contamination levels in selected agricultural soils. An ultrasonic assisted sequential extraction procedure derived from three-step BCR method was used for fractionation of trace elements. The total concentration of trace elements in soil samples was obtained by total digestion method in soil samples with aqua regia. The results of the extractable fractions revealed that most of the target trace elements can be transferred to the human being through the food chain, thus leading to serious human health. Enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), risk assessment code (RAC) and individual contamination factors (ICF) were used to assess the environmental impacts of trace metals in soil samples. The EF revealed that Cd was enriched by 3.1-7.2 (except in Soil 1). The Igeo results showed that the soils in the study area was moderately contaminated with Fe, and heavily to extremely polluted with Cd. The soil samples from the unplanted field was found to have highest contamination factor for Cd and lowest for Pb. Soil 3 showed a high risk for Tl and Cd with RAC values of greater than or equal to 50%. In addition, Fe, Ni, Cu, V, As, Mo (except Soil 2), Sb and Pb posed low environmental risk. The modified BCR sequential extraction method provided more information about mobility and environmental implication of studied trace elements in the study area.

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.

Speciation of inorganic selenium in environmental samples after suspended dispersive solid phase microextraction combined with inductively coupled plasma spectrometric determination

A rapid and effective suspended dispersive solid phase microextraction (SDSPME) was developed for the speciation of inorganic selenium using alumina nanoparticles functionalized with Aliquat-336. The target analytes were preconcentrated and determined by inductively coupled plasma optical emission spectrometry. Alumina nanoparticles were characterized using XRD, BET, SEM and EDX while the functionalized nano-Al2O3 was characterized by FTIR. The effect of pH of the solution on speciation Se in water samples was optimized separately. It was observed that when the pH values of sample solution ranged from 2.0 to 7.0, successful separation of inorganic Se species was achieved. The percentage recoveries for Se (IV) and Se (VI) were >90% and 5%, respectively. The two-level fractional factorial design was used to optimize experimental parameters affecting the preconcentration system. Under optimal conditions, the enrichment factor (EF), limit of detection (LOD) and limit of quantification for Se (IV) were found to be 850, 1.4ngL(-1,) and 4.6ngL(-1), respectively. Furthermore, intra-day and inter-day precisions expressed in terms of relative standard deviation (RSD) were found to be 1.9% and 3.3%, respectively. The effect of coexisting ions on the recovery of Se (IV) was investigated. The accuracy of the developed method was checked by analysis of standard reference material (NIST SRM 1643e). The optimized method was applied for the determination of targets in surface water samples.

Determination of As, Cr, Mo, Sb, Se and V in agricultural soil samples by inductively coupled plasma optical emission spectrometry after simple and rapid solvent extraction using choline chloride-oxalic acid deep eutectic solvent

A rapid, simple and green ultrasound-assisted extraction method using deep eutectic solvents (DES) for extraction of As, Cr, Mo, Sb, Se and V in soil samples, has been developed. Choline chloride-oxalic acid based DES was used as a solvent. The target analytes were subsequently quantified using inductively coupled plasma optical emission spectrometer (ICP OES). The parameters that affect the extraction of the target analytes was optimized using standard reference material of San Joaquin soil (SRM 2709a). In the optimization step, a two-level full factorial experimental design was used. The factors under investigation include extraction time, sample mass and acid concentration. Under optimized conditions, limits of detection (LOD) and limits of quantification (LOQ) ranged from 0.009 to 0.1 and 0.03-0.3µgg-1, respectively. The repeatability (n=20) estimated in terms of relative standard deviation (%RSD) ranged from 0.9% to 3.7%. The accuracy of the proposed method was carried out using SRM 2709a. The obtained and certified/ indicative values were statistically in good agreement at 95% confidence level. The proposed method applied for quantification of As, Cr, Mo, Sb, Se and V in real soil samples. For comparison, the analytes of interest were also determined using a conventional acid digestion method. According to the paired t-test, the analytical results were not significant differences at 95% confidence level. The method was found to be accurate, precise and environmentally friendly.

Fast microwave-assisted green synthesis of xanthan gum grafted acrylic acid for enhanced methylene blue dye removal from aqueous solution

In the present project, graft polymerization was employed to synthesis a novel adsorbent using acrylic acid (AA) and xanthan gum (XG) for cationic methylene dye (MB+) removal from aqueous solution. The XG was rapidly grafted with acrylic acid (CH2=CHCOOH) under microwave heating. Fourier-transform infrared spectroscopy (FTIR), Proton Nuclear magnetic resonance spectroscopy (1H NMR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Thermal gravimetric analysis (TGA) techniques were used to verify the adsorbent formed under optimized reaction conditions. Optimum reaction conditions [AA (0.4M), APS (0.05M), XG (2gL-1), MW power (100%), MW time (80s)] offer maximum %G and %GE of 484 and 78.3, respectively. The removal ratio of adsorbent to MB+ reached to 92.8% at 100mgL-1. Equilibrium and kinetic adsorptions of dyes were better explained by the Langmuir isotherm and pseudo second-order kinetic model respectively. The results demonstrate xanthan gum grafted polyacrylic acid (mw XG-g-PAA) absorbent had the universality for removal of dyes through the chemical adsorption mechanism.

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).