A.B. Farag

Polyurethane foams and microspheres in analytical chemistry : Improved liquid-solid, gas-solid and liquid-liquid contact via a new geometry of the solid phase

Abstract This review covers the following aspects: the preparation and properties of polyurethane foams and of open-pore polyurethane microspheres; the use of unloaded polyurethane foams for the separation and enrichment of inorganic and organic species in aqueous solution, and for the collection of pesticide vapours in air; and the application of polyurethane foams with physically immobilized reagents (hydrophobie reagents such as organic extractants and chelating agents, heterogeneous ion-exchange foams and inorganic precipitates). Polyurethane foams with anchored functional groups and specially treated polyurethane foams are then discussed. Finally the use of open-pore polyurethane microspheres in gas-solid chromatography, gas-liquid chromatography, and low pressure liquid chromatography is outlined.

Plasticized open-cell polyurethane foam as a universal matrix for organic reagents in trace element preconcentration: Part I. Collection of silver traces on dithizone foam

Abstract The preparation of plasticized foam containing dithizone or zinc dithizonate is described. The foam was used successfully for the rapid and quantitative collection of trace amounts of silver in batch and column experiments. The preconcentration of small amounts of silver from dilute aqueous solutions was found to be possible. The effects of different plasticizers, pH of the aqueous phase, and dithizone concentration in the foam, on the collection rate of silver were critically investigated.

Reversed-phase foam chromatography. Separation of palladium, bismuth and nickel in the tributyl phosphate-thiourea-perchloricacid system

Abstract The feasibility of using TBP-loaded polyurethane foams as column fillings in reversed-phase chromatography was examined and their capacities were determined. Separation of nickel, bismuth, and palladium was achieved. The effect of flow-rate, temperature and ratio of the separated ions on the efficiency of separation was tested. Elution with high flow-rate affected the efficiency of the column at 25° but not at higher temperature (e.g. 35°). Once the column was prepared, it could be used several times without affecting its efficiency.

Plasticized open-cell polyurethane foam as a universal matrix for organic reagents in trace element preconcentration. Part II. Collection of mercury traces on dithizone and diethyldithiocarbamate foams

The analytical suitability of zinc dithizonate foam for the collection and preconcentration of traces of mercury(II) has been examined. The effect of pH, plasticizer and chelating agent concentration on the collection rate of mercury has been critically investigated. The capacity for mercury(II) of a TBP-plasticized zinc dithizonate foam at pH 6 is 23.4 μeq g−1. The effect of plasticizer on the rate of recovery of mercury with sodium thiosulphate solution is also discussed. The preparation of zinc diethyldithiocarbonate foam is described. Traces of mercury(II) can also be collected rapidly and quantitavely by this foam.

Chromofoams qualitative and semi-quantitative tests with chromogenic organic reagents immobilized in plasticized open-cell polyurethane foams

Abstract Polyurethane foams treated with organic reagents in a plasticizer solution can be used for simple, rapid, sensitive, and selective detection and semiquantitative determination of metal ions from dilute aqueous solutions. Batch techniques can be used for simple tests which provide sensitivity as good as, or better than, that attainable by normal spot tests. The application of reagent-treated foam columns for the detection and semiquantitative determination of metal ions from extremely dilute aqueous solutions is advantageous; ions in the p.p.b. range can be detected after passage of 1 l of solution at a fast rate. The use of these techniques for zinc(II) and lead(II) with dithizone, copper(II) with rubeanic acid, and cobalt(II) with thiocyanate-Amberlite LA-l, is described.

Plasticized open-cell polyurethane foam as a universal matrix for organic reagents in trace element preconcentration : Part III. Collection of cobalt traces on 1-nitroso-2-naphthol and diethyldithiocarbamate foams

Abstract The preparation of 1-nitroso-2-naphthol and diethylammonium diethyldithiocarbamate foams is described. The effect of pH, plasticizer and shaking time on the collection efficiency of cobalt(II) on these reagent foams has been investigated. The collection of various concentrations of cobalt(II) on the proposed reagent foams packed in columns is quantitative at flow-rates of 5–6 ml cm-2 min-1.

Polyurethane-pyridylazonaphthol foams in the preconcentration and separation of trace elements

Abstract The feasibility of using PAN—polyether and polyester polyurethane foams in batch and column operations has been examined. The effects of pH, plasticizer and various anions present in the aqueous solution on the extraction behaviour of cobalt, iron and manganese have been investigated. In dynamic systems, the effect of flow rate on the extraction efficiencies of these metal ions has been investigated. The uptake of cobalt(III) and manganese(II) on PAN—polyester foam columns is quantitative at flow rates up to 10 ml min-1 and 2 ml min-1, respectively. The retention of iron(III) by the foam column is not quantitative even at a flow rate of 1 ml min-1. Preconcentration of cobalt and its separation from various concentrations of manganese are successful..

The recovery of gold from thiourea solutions with open-cell polyurethane foams

Abstract The recovery of the gold-thiourea complex from aqueous solutions with TBP-loaded and unloaded polyurethane foams was investigated in batch experiments. The rates of adsorption of the gold complex on various types of loaded and unloaded foams were studied in detail and compared with the rate of adsorption on active carbon. Loaded and unloaded polyurethane foams of the polyether or polyester type behaved similarly to active carbon. The adsorption capacity of the foams was lower than that of active carbon but the use of foam simplifies the procedure by eliminating the filtration process which is necessary with carbon.

Reversed-phase foam chromatography : Chemical enrichment and separation of gold in the tributylphosphate-thiourea-perchloric acid system

Abstract Gold(III) is quantitatively extracted from acidic solution of thiourea into tri- n -butyl phosphate (TBP). The extracted species contains one molecule of thiourea and four molecules of TBP for each atom of gold. On short columns of TBP-loaded polyurethane foam, gold(III) can be separated from many other elements by retention from 0.1 M perchloric acid solution containing 3% thiourea and 1% sodium perchlorate. Flow-rates of 50–60 ml min −1 are possible. Trace amounts of gold can be separated quantitatively from high concentrations of Zn 2+ , Co 2+ , Ni 2+ , Fe 3+ , Sb 3+ , Cu 2+ , Bi 3+ and Pd 2+ , which have a negligible effect on the rate of adsorption of the gold-thiourea complex. The chemical enrichment of gold from dilute aqueous solutions is also possible.

Reversed-phase foam chromatography: Redox reactions on open-cell polyurethane foam columns supporting tetrachlorohydroquinone

Abstract The use of elastic polyurethane foam as a support for chloranil was proved successful. Reductions of cerium(IV), vanadium(V) and iron(II) on foam-filled columns were carried out quantitatively and rapidly. The effect of flow-rate and temperature on the reduction of each metal ion was examined in detail. Cerium(IV) was reduced quantitatively on passing through the foam-redox column at flow-rates of 2–11 ml min -1 at room temperature. The reduction of vanadium(V) and iron(III) was slower; complete reduction occurred only at flow-rates up to 4 and 2 ml min -1 for V(V) and Fe(III), respectively. At 35°, however, it was possible to use flow-rates of 7 and 6 ml min -1 for the quantitative reduction of V(V) and Fe(III), respectively.