Nalini Parthasarathy

Hollow fiber based supported liquid membrane: a novel analytical system for trace metal analysis

Abstract A new versatile tool for speciation of trace metals, in particular Cu, Pb and Cd based on a hollow fiber supported liquid membrane (HFSLM) consisting of 1,10-didecyl diaza 18-crown-6, fatty acid and a mixture of toluene and phenylhexane (1 + 1) has been studied for application in natural water conditions. Two types of single hollow fiber modules i.e. non flow and flow systems for free metal ion separation and preconcentration were used. The effect of target elements, sample volume, target metal concentration, and flow rates of sample solution in the case of the flow system on the preconcentration factor for a given receiver solution volume (ca 50–60 μl) placed in the lumen of the membrane) have been studied. High preconcentration factors in the range 100–3000 for Cu, Pb and Cd, for preconcentration times in the range 5–120 min were found using sample and receiver solution volumes of 250 ml and 60 μl, respectively. Preconcentration factors were found to be independent of the initial concentration of target elements in the sample and dependent on initial sample volume. Long term stabilities of these membranes showed that they are stable for at least seven days of continuous use. The results of these studies suggest that by combining SLM with sensitive analytical detectors e.g., voltammetric ones, detection limits of below 10 −10 mol l −1 can be achieved.

Capabilities of supported liquid membranes for metal speciation in natural waters : application to copper speciation

The transport of Cu2+ through a supported liquid membrane (SLM) consisting of 1,10-didecyldiaza-18-crown-6, a fatty acid and a mixture of toluene and phenylhexane (1 + 1) under natural water conditions was studied. Long-chain fatty acids having various numbers of carbon atoms Cn (n = 10-18) were tested to obtain a reasonably high Cu2+ transport rate. The rate of transport of Cu(II) was found to be fast when lauric acid (n = 12) was included in the membrane phase. The transport Cu2+ by the SLM in the presence of Cu(II) complexants such as Tiron and oxalate was investigated. The results showed that the flux of Cu(II) through the membrane depends specifically on the free metal ions. These results were verified by means of a Cu(II) ion=selective electrode. The SLM was applied to the determination of Cu2+ in fresh waters and the results were compared with those obtained by ultrafiltration.

Combined use of calcium salts and polymeric aluminium hydroxide for defluoridation of waste waters

The combined use of calcium salt and polymeric aluminium hydroxide, P, for treatment of fluoridated waste water has been described. In the proposed method of treatment the calcium ions acts as the precipitant and polymeric aluminium hydroxide as the coagulant. At low fluoride concentrations (2 × 10−3 M) the precipitation reaction of calcium fluoride is a slow process. The residual fluoride concentrations found experimentally approached the theoretically predicted values only at high calcium concentrations (| F | t/ | Ca | I molar ratio = 0.24) and for long equilibration times. The addition of calcium fluoride seeds (approx. 20 mg 1−1) accelerated the precipitation process and the results obtained for the residual fluoride concentrations were close to the theoretically calculated ones regardless of the calcium ion concentration used. Under these conditions fine CaF2 precipitate with poor settleability was formed. The addition of small amounts of polymeric aluminium hydroxide, P, (F/Al molar ratio = 10) greatly facilitates the settleability of the precipitate. The advantage of using P over alum for the removal of fluoride is that less concentration of the former is required and the reproducibility of the results are good. The effect of sulphate on the precipitation of calcium fluoride has been also studied. Tests with fluoride containing waste water collected from aluminium industry showed that fluoride can be effectively removed.

Voltammetric study of humic and fulvic substances V. Interpretation of metal ion complexation measured by anodic stripping voltammetric methods

Abstract The interpretation of anodic stripping voltammetric (ASV) peaks for measuring the complexation reactions of metal ions with aquatic fulvic and humic compounds is difficult due to the simultaneous influence of several different phenomena, in particular the heterogeneous nature of fulvic compounds, the fact that the ligand is not in excess compared with the metal ion during the stripping step, the slow diffusion of the complexes compared with the free metal ions, and the adsorption of fulvic compounds on the electrode. The influences of these phenomena are briefly reviewed with regards to complexation measurements using direct polarographic techniques. The results obtained by ASV on a hanging mercury drop electrode (HMDE), for the complexation of Pb(II) by aquatic pedogenic refractory organic matter (often referred to as pedogenic water fulvic acids), are then described and interpreted on these bases. The relative importance of the above-mentioned phenomena in the ASV mode, together with their influence on stripping polarography curves and on measurements of complexation capacities are discussed. It has been shown that the recording of peak current and potential as a function of electrolysis time is a very powerful means for facilitating a correct interpretation.

Importance of speciation methods in analytical control of water treatment processes with application to fluoride removal from waste waters

Analytical methods of speciation for the control of water treatment processes, particularly for the removal of fluoride by aluminium hydroxide polymers as precipitant, have been discussed. It has been shown that combination of ultrafiltration with spectroscopic methods and fluoride ion-selective electrode offers a powerful means for the control of both the precipitant and pollutant, e.g. fluoride. 27Al n.m.r. has been used for the identification of hydrolytic products of aluminium(III) and the ultrafiltration technique has been applied for the separation of the active polymer. The hydrolytic products were also characterized by timed spectrometric method. The interaction between aluminium hydroxide polymer and fluoride was studied by means of fluoride ion-selective electrode, ultrafiltration and atomic absorption spectrometry. The usefulness of these speciation methods for choosing the best conditions for water treatment process is discussed. By applying them for the removal of fluoride, it was found that the fluoride levels can be brought down to less than 10 mg l−1, the limit set by Swiss regulatory body for discharge of waste water. The importance of using such speciation methods for evaluating the possible impact of the “products” of the water treatment (dissolved species in treated water, discharged solid) is also emphasized.

Study of the behaviour of solid-state membrane electrodes : Part II. Role of adsorption of fluoride ions on fluoride ion-selective electrode and determination of solubility of the membrane☆

Abstract The phenomena limiting the sensitivity of the fluoride-selective electrode are described. Although the interference of electrolyte ions or fluoride impurities can play a part in this lower detection limit, it seems that the adsorption of fluoride ions at the membrane-solution interface and the solubility of the electrode crystal are the two principal parameters. The solubility of the electrode crystal under different conditions was estimated.

Study of the behaviour of solid-state membrane electrodes : Part I. Role of various factors on the limits of sensitivity of chloride and fluoride electrodes

Abstract A study of the behaviour of the chloride-selective electrode in the concentration range below the linear response region, has shown that the nonlinearity is principally due to three factors: the solubility of the membrane, the concentration of chloride impurities and the interference of ions of the background electrolyte or other impurities. Similar studies with fluoride electrodes have shown that, in addition to these factors, other parameters also play an important role.

Cadmium Adsorption by Chlamydomonas reinhardtii and its Interaction with the Cell Wall Proteins

Environmental Context. In natural waters, trace metals levels are largely controlled by microbiology; organisms take up, metabolize, store, and detoxify the metals. However, aquatic organisms may regulate their own uptake via dynamic processes that result in a system that is far from equilibrium. By examining the model title alga with a battery of techniques, a more realistic assessment of metal uptake and metal regulatory processes could be gained. Abstract. Cadmium adsorption by a wild type strain of Chlamydomonas reinhardtii and a cell wall-less mutant was quantified as a function of Cd speciation in a well-defined aqueous medium. For both strains, Cd adsorption to the cell surface was not predicted by a single-site (Langmuirian) model. Indeed, no saturation of the cell wall was observed, even for Cd concentrations in excess of 5 × 10−3 M. A continual production of Cd binding sites appeared to be responsible for the observed increase of Cd adsorption with time. SDS-page separations and measurements of the protein content of algal supernatants demonstrated that organic matter was released by the algae, both in the presence and absence of Cd. Both the nature (e.g. polysaccharides, proteins) and the quantity of exudate production was influenced by the physicochemistry of the external medium. Measurements using the permeation liquid membrane (PLM) and anodic stripping voltammetry (ASV) demonstrated that dissolved cadmium was rapidly complexed by the organic exudates produced by the algae.

A study of the behaviour of solid-state membrane electrodes: Part IV. Experimental studies of the response time

Some ot the factors governing the response time of the fluoride-selective and chloride-selective electrodes have been investigated. The results of E—t and conductance measurements indicate that dissolution and charge-transfer processes control the ion-seiective electrode kinetics. The temperature coefficients of the rate constants for dissolution of the chloride electrode membrane, determined by E—t curves and conductimetric measurements, are similar. The results, and the fact that the dissolution is a second-order process, indicate that surface processes play the predominant role in electrode kinetics near equilibrium.

Role of extracellular compounds in Cd-sequestration relative to Cd uptake by bacterium Sinorhizobium meliloti.

The role of bacterially derived compounds in Cd(II) complexation and uptake by bacterium Sinorhizobium meliloti wild type (WT) and genetically modified ExoY-mutant, deficient in exopolysaccharide production, was explored combining chemical speciation measurements and assays with living bacteria. Obtained results demonstrated that WT- and ExoY-strains excreted siderophores in comparable amounts, while WT-strain produced much higher amount of exopolysaccharides and less exoproteins. An evaluation of Cd(II) distribution in bacterial suspensions under short term exposure conditions, showed that most of the Cd is bound to bacterial surface envelope, including Cd bound to the cell wall and to the attached extracellular polymeric substances. However, the amount of Cd bound to the dissolved extracellular compounds increases at high Cd(II) concentrations. The implications of these findings to more general understanding of the Cd(II) fate and cycling in the environment is discussed.