This paper presents the synthesis and application of 5-(2-hydroxy-4-nitrophenylazo)-rhodanine (HNAR) as a new chromogenic reagent for the determination of gold. Based on the rapid reaction of gold with HNAR and the solid phase extraction of the coloured chelate with a reversed phase polymer-based C18 cartridge, a highly sensitive, selective and rapid method for the determination of gold has been developed. In the presence of 0.05-0.5 mol L-1 of phosphoric acid solution and emulsifier-OP medium, HNAR reacted with gold to form a red chelate of a molar ratio 1:3 (gold to HNAR). This chelate was enriched by the solid phase extraction with a polymer-based C18 cartridge and the retained chelate was eluted from the cartridge with dimethyl formamide (DMF). An enrichment factor of 100 was achieved. In DMF medium, the molar absorptivity of the chelate was found to be 1.51 x 105 L mol-1 cm-1 at 496 nm. Beer's law was obeyed in the range of 0.01~2 µg mL-1. The relative standard deviation for eleven replicates with a concentration of 0.5 µg L-1 level was 2.31%. The detection limit based on three times the standard deviation was 0.01 µg L-1 in the original sample. This method was applied to the determination of gold with good results.
Results of speciation studies of nickel and chromium in wastewater, surface and groundwater systems using flame atomic absorption spectrometry (FAAS), graphite furnace atomic absorption spectrometry (GFAAS) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) are presented. Dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were used as complexing agents for DPAdCSV determination of nickel and chromium, respectively, at a hanging mercury drop electrode (HMDE). Total nickel was in the range 3091-3201 mg L-1 in wastewater from an electroplating plant, 8.1-14.4 µg L-1 in surface water (freshwater) and 6.38-16.95 µg L-1 in groundwater. Total chromium was in the range 34.99-37.03 mg L-1 in electroplating wastewater and 15.8-571.0 mg L-1 in tannery effluents. Trace levels of chromium were detected in surface water (3.09-17.42 µg L-1) and groundwater (18.01-36.39 µg L-1). While most of the metal forms were found to be present in the CSV-labile fraction in the wastewater from the electroplating plant (mean of 67.9% for Ni and 79.8% for Cr), less than 5% of the total metal was present as CSV-labile fraction in tannery effluents, surface and groundwater samples. The tannery effluent was found to have very high complexation capacity (about 3 mg of Cr /L of effluent, i.e. 57.8 µM Cr). This complexing capacity of tannery effluent may have a potential application in environmental remediation.
The sorption of lead on palm kernel fibre, an agricultural waste product, has been studied. The sorption process was studied as a function of initial lead concentration and initial solution pH. The percentage lead removal was found to increase with increasing initial solution pH up to pH 5 and then to decrease as pH was increased to 6. The pseudo-second order kinetic rate model was employed in the analysis of the kinetics of lead uptake onto the palm kernel fibre. The results show that the pseudo-second order model fits the experimental data with high coefficients of determination (r2). The equilibrium sorption capacity was found to be 33.33 mg -1 when 1.0 g of fibre was contacted with 90 mgdm-3 of lead solution at pH 5. Mathematical expressions were derived to relate the pseudo-second order rate constant, k, and the change in solution pH with initial lead concentration.
The emulsification of used lubricating oil as a method of sample preparation, preceding the determination of wear-metals in the oil using ICP-OES, was compared to the preparatory methods of ashing and dilution. The oil samples were treated with acid and emulsified in water (1% w/w) using tetralin as a solvent and Triton X-100 as a surfactant. The performance characteristics (detection limits, accuracy, precision and spike recovery) of the emulsion methodology were evaluated. The calibration for the emulsion method compared favourably with the traditional methods of sample preparation. The detection limits for the emulsion method were lower in certain cases than those for ashing and dilution. The precision was on average approximately 2% RSD or less, except where the sample's concentration value was close to the detection limit.
Throughput of students is a concern for academic departments especially since it will be the basis of a new funding formula for tertiary institutions. In order to reduce content for increased mastery, and ensure student engagement with chemical concepts, tutorials were introduced for two of the second year chemistry sub-disciplines at UCT in the place of some formal lectures. The impact of this innovation was investigated using questionnaires, interviews and a study of opportunistic data such as examination results. Analysis of the data showed that the overall pass rate increased noticeably as did the number of students achieving high marks. Student, tutor and lecturer feedback lent credence to the belief that the improvement was largely due to the introduction of the tutorial scheme. In addition, some noteworthy differences between the sub-disciplines were identified. Some of these differences were attributed to the lecturer's understanding of his own teaching.