W. Haerdi

The use of ultrafiltration for the separation and fractionation of organic ligands in fresh waters

Abstract The effects of various experimental conditions on the results obtained by using membrane filtration for the separation and fractionation of organic matter in fresh waters (mainly fulvic and humic substances) are described. The technique used (washing or concentration) and the initial concentration of the organic matter to be filtered are the most critical factors. The technique is used for the fractionation of eight water samples, one sample of peat interstitial water, five water extracts of soil and four water samples obtained by decomposition of leaves. The results are compared. A comparison is also made with results cited in the literature.

Study of the complex formation of copper(II) by humic and fulvic substances

A study of the complexation of copper(II) by fulvic substances, based on ion-selective electrode measurements, is reported. The influences of the copper concentration (10-6 –1O-4 M), fulvic acid concentration (2–100 mg 1-1), pH (3–8) and calcium concentration (10-4–5 × 1O-3 M) are given particular attention. The effects of statistical errors on the measurement of the values of the complex-formation parameters are considered. These parameters are measured for various surface-water samples, aqueous soil extracts, peat water and solutions of organic matter formed by in vitro decomposition of leaves. In general, these parameters vary little with actual source for a particular type of water.

Voltammetric study of humic and fulvic substances: Part I. Study of the factors influencing the measurement of their complexing properties with lead

Abstract A detailed, qualitative, investigation of the behaviour of lead complexes with fulvic substances has been carried out using several polarographic techniques, e.g d.c. polarography, a.c. polarography, normal and differential pulse polarography and cyclic voltammetry. The mercury drop electrode was used for this study. It is shown that under the conditions used (pH∼6) the charge transfer process is reversible, the complexes are labile and the adsorption of fulvic acids and fulvic complexes occurs on the electrode. The implications of these results, with regard to the use of the various amperometric titrations for the measurement of the complexing capacity of natural waters, are discussed.

Extraction of artemisinin and artemisinic acid from Artemisia annua L. using supercritical carbon dioxide.

Artemisinin (an antimalaric compound) and its major precursor artemisinic acid, isolated as the active principles of the medicinal plant Artemisia annua L., were extracted by supercritical fluid extraction (SFE) and analyzed by supercritical fluid chromatography (SFC) using a capillary column, coupled with a flame ionization detector (FID). With optimized operating conditions, artemisinin and artemisinic acid were quantitatively extracted at a flow-rate of 2 ml min-1 in less than 20 min. The supercritical fluid was composed of carbon dioxide and 3% methanol with temperature and pressure fixed at 50 degrees C and 15 MPa, respectively. From the kinetic curves, it appears that the extraction of artemisinin is not limited by the diffusion of the analyte from the plant into the extraction fluid but rather by the elution process. These conditions avoided degradation of the analyte and gave clean extracts ready to be analyzed by SFC. The SFE-SFC-FID method was successfully applied to six samples of A. annua containing various concentrations of artemisinin and artemisinic acid. Results were compared with two conventional liquid solvent extraction processes.

Analysis and characterization of natural organic matters in freshwaters: I. Study of analytical techniques

Several analytical techniques have been studied for the analysis and characterization of humic and fulvic compounds of freshwaters. DOC analysis, thermogravimetry, UV absorbance, fluorescence, cascade ultrafiltration, freezing concentration techniques are particularly discussed. The effects of several important factors, e.g. nature and concentration of organic matters, pH, and concentrations of several important factors, e.g. nature and concentration of organic matters, pH, and concentrations of inorganic constituents (particularly Fe(III), Si(IV), Ca(II), HCO3−) on the analytical results, were studied.Determination of A/DOC, F/DOC and fractionation by cascade ultrafiltration were found to be useful means to characterize the nature of organic matter. But it must be noted that the results of these techniques can be strongly affected by the concentration of fulvic compounds. Adsorption on freshly precipitated CaCO3 could be one of the important processes of elimination of organic matter.

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.

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.

The evaporative light scattering detector : some applications in pharmaceutical analysis

The evaporative light scattering detector allows direct detection of all non-volatile compounds regardless of their chemical structure, and therefore it is a valuable tool to determine compounds without chromophores. This detector can be coupled to liquid chromatography and packed supercritical fluid chromatography. In this article, the principles are described and some examples of application to pharmaceutical analysis are given.

Voltammetric study of humic and fulvic substances: Part III. Comparison of the capabilities of the various polarographic techniques for the analysis of humic and fulvic substances

Abstracts A systematic study of the influence of FA and HA on the current measured by the various polarographic techniques is presented. In most of the techniques (ac polarography, pulse polarography, Kalousek technique) one observes mainly a modification of the capacitive current which may be used for the quantitative analysis of FA. For this purpose the best techniques are ac polarography and the decrease in the polarographic maximum of O 2 . The sensitivity of these techniques is about 1 mg l −1 . A comparison of the results of the last two techniques is given for FA of various origin. Comparison is also made with model compounds in the case of ac polarography.

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.