On-site preconcentration and trace metal ions determination in the Okavango Delta water system, Botswana

Microcolumns containing 8-hydroxyquinoline azo-immobilized on controlled pore glass were incorporated in a field sampler for on-site collection, isolation and preconcentration of trace metal ions in waters of the Okavango Delta, Botswana. Sequestered trace metal ions were recovered by elution with 0.5 ml of 1.5 M nitric acid, and determined by graphite furnace atomic absorption spectrometry (GFAAS). This sampling and enrichment method minimizes sample contamination, and collection of large volumes of water samples for transporting, over long distances, to analytical laboratories is avoided.Data reported comprise one of the initial surveys on trace metal ion concentrations in waters of the Okavango Delta, Botswana. In waters with more efficient mixing, dissolved metal ion concentrations found were generally low with slightly elevated levels of manganese (7-19 μg l⁻¹), zinc (2.7-4.8 μg l⁻¹), nickel (0.2-2.5 μg l⁻¹) and copper (0.3-2.1 μg l⁻¹). For each trace metal ion, concentration levels seem to reflect zones of varying water conveyance, and show no obvious temporal and spatial variations apart from a slight increment from the inlet in the upper Delta to the outlets in the lower Delta.     

Determination of orthophosphates using a macro segmented flow analyzer (MSFA) based on colorimetric detection

Fabrication of a macro segmented flow analysis (MSFA) system based on reconfiguration of the manifold by adjustment of the sample/reagent ratio, has been found to produce a sensitive method for orthophosphate analysis based on colorimetric detection at 880 nm. Optimization of sample tube length, reaction temperature and molybdate concentration in the carrier solutions has been carried out. The larger sample tube internal diameter led to the combined advantages of better sensitivities, wider working range and higher sample throughput over most existing methods. Using the optimized conditions of 50.0 cm sample tube length (1.6 mm i.d.), 37.0 °C reaction temperature and 0.0113 M molybdate concentration in the carrier solution, the calibration model for orthophosphate standard solutions was found to be linear (y = 0.04895x + 0.003561; correlation coefficient, r²=0.9970) over the working range 0.01-2.00 mg l⁻¹ orthophosphate. The volume of the sample injected was 1.396 ml at a flow rate of 6.0 ml min⁻¹. The sample throughput of this MSFA method was 40 samples per an hour, with a detection limit of 4.0 μg l⁻¹, and %R.S.D.’s below 5%. The MSFA method was successfully applied to analysis of water and wastewater samples.     

Speciation studies of nickel and chromium in wastewater from an electroplating plant

A speciation scheme involving the use of flame atomic absorption spectrometry (FAAS) and differential pulse adsorptive cathodic stripping voltammetry (DPAdCSV) techniques was applied to studies of nickel and chromium in wastewater from a nickel-chrome electroplating plant. Dimethylglyoxime (DMG) and diethylenetriaminepentaacetic acid (DTPA) were employed as complexing agents for adsorptive voltammetric determination of Ni and Cr, respectively. Cr(III) and Cr(VI) were determined by exploiting differences in their reactivity towards DTPA at HMDE. Total dissolved metal content was in the range 2906-3141 and 30.7-31.2 mg l⁻¹ for Ni and Cr, respectively. A higher percentage of the metal was present as labile species (mean value of 67.9% for Ni and 79.8% for Cr) suggesting that strongly binding ligands are not ubiquitous in the sample. About 77.8% of Cr was found to exist in the higher oxidization state, Cr(IV). Results on effect of dilution on lability of the metal forms in the sample using DPAdCSV showed slight peak shifts to a more negative (cathodic) value by −0.036 V for Ni and −0.180 V for Cr with a dilution factor of 100, while peak intensity (cathodic current) remained fairly constant.     

A study of microdialysis sampling of metal ions

A study of the extraction fraction (EF) of metal ions Cd, Cr, Cu, Ni and Pb sampled by microdialysis from a quiescent aqueous solution is presented. A concentric type of microdialysis probe equipped with either one of two polysulfone membranes supplied by different manufacturers or a polyether sulfone membrane, all with a 10 mm effective dialysis length was used for these investigations. EF for metal ions achieved after microdialysis sampling were evaluated for membranes exhibiting a cut-off molecular weight of 3, 5, 10 and 30 kDa. The EF for all metal ions showed a dependency on membrane cut-off as well as membrane material. For Cr EFs of 0.70 and 0.80 were achieved at 1 μl/min using a polysulfone and polyether sulfone membrane, respectively, both with a 30 kDa cut-off molecular weight. Using the polysulfone membrane, Cr showed the highest EF and Pb had the lowest at 0.1. The polyether sulfone membrane achieved an EF of 0.95 for Ni and the lowest EF value was for Cu at 0.35. In these studies it is shown that pH as well as the inclusion of an optimal concentration (0.20 M) of 8-hydroxyquinoline (8-HQ) in the perfusion liquid can enhance the EF of metal ions. Microdialysis was also used to sample for metal ions from wastewater and from whole tomatoes grown using sewage sludge manure in order to demonstrate the potential to apply it to these complicated matrices.     

Coulter particle analysis used for studying the effect of sample treatment in slurry sampling electrothermal atomic absorption spectrometry

This work focuses on the potential of using a Coulter particle analyzer for method development in slurry sampling ETAAS. Plant materials were used as an example; the particle size distributions obtained after grinding in a mixer mill were measured for ground material and slurries prepared from flowers, leaves, stem and roots of the same plant material. Normally the particle size distribution is reported either as number of particles versus size or volume of particles versus size. The advantage of using the latter mode of reporting is demonstrated. It is shown that detailed information about the larger particles is lost when the distribution is reported in terms of the number-percentage. In the present case, 60 min of grinding gave similar size distribution for all the plant materials. All particles had diameters less than 50 μm and the calculated number of particles per mg was 6–8 × 10⁷. It is shown that the ultrasonic agitation used to homogenize the slurries, prior to injection of the sample, also had an effect on the particle size distribution. Received: 16 February 1998 / Revised: 20 July 1998 / Accepted: 26 July 1998     

Association of Molybdenum Ionic Species with Alumina Surface

The adsorption isotherms at 25, 45, and 65 degrees C of molybdenum solutions of concentration ranges between 10(-3) and 3x10(-2) M(Mo) (pH 4-5) on different alumina samples are investigated. The analysis is conducted using a modified Frumkin isotherm which takes a more realistic account of the lateral interaction between adsorbed species and considers that the adsorption takes place on the most basic OH groups on the surface of alumina. The results are discussed in view of the difference in solutions speciation, and the changes in the pH of the remaining supernatant solutions. The solution temperature, PZC of the used aluminas, the configuration of the basic OH groups on their surface, and the pore structure have been shown to intervene effectively. Copyright 2000 Academic Press.     

Coulter particle analysis used for studying the effect of sample treatment in slurry sampling electrothermal atomic absorption spectrometry

This work focuses on the potential of using a Coulter particle analyzer for method development in slurry sampling ETAAS. Plant materials were used as an example; the particle size distributions obtained after grinding in a mixer mill were measured for ground material and slurries prepared from flowers, leaves, stem and roots of the same plant material. Normally the particle size distribution is reported either as number of particles versus size or volume of particles versus size. The advantage of using the latter mode of reporting is demonstrated. It is shown that detailed information about the larger particles is lost when the distribution is reported in terms of the number-percentage. In the present case, 60 min of grinding gave similar size distribution for all the plant materials. All particles had diameters less than 50 μm and the calculated number of particles per mg was 6–8 × 10⁷. It is shown that the ultrasonic agitation used to homogenize the slurries, prior to injection of the sample, also had an effect on the particle size distribution.