Chromotropic acid-functionalized polyurethane foam: A new sorbent for on-line preconcentration and determination of cobalt and nickel in lettuce samples

A chromotropic acid-functionalized polyurethane foam has been developed for use in an on-line preconcentration system for cobalt and nickel determination. The packing material was prepared by covalent coupling of chromotropic acid with the polyurethane foam through an azo group. Co and Ni ions were sorbed in the mini-column, from which they could be eluted directly to the nebulizer-burner system of a flame atomic absorption spectrometer. Elution of cobalt and nickel from the mini-column can be accomplished with 0.50 and 0.75 M HCl solutions, respectively. The enrichment factors obtained were 22 (Co) and 27 (Ni), for 60 s preconcentration time, and 57 (Co) and 59 (Ni), if a preconcentration time of 180 s was used. Under the optimum conditions, the proposed procedure allowed the determination of metals with detection limits of 0.43 (cobalt) and 0.52 microg/L (nickel), respectively, on using preconcentration periods of 180 s. The accuracy of the developed procedure was evaluated by analysis of the certified reference materials NIST 1515 Apple Leaves and NIST 1570a Spinach Leaves. The method was applied to the analysis of lettuce samples. The contents of cobalt in the samples analyzed varied from 0.75 to 0.98 microg/g. Nickel was not detected in the lettuce samples.     

Separation and determination of some trivalent metal ions using rhodamine B grafted polyurethane foam

The incorporation of rhodamine B into polyurethane foam matrix was prepared by mixing the rhodamine B with polyol (polyether) prior to the addition of diisocyanate reagent to form the polyurethane foam material. Rhodamine B grafted polyurethane foam (Rod.B-PUF) was found to be very suitable for the separation and preconcentration of trivalent metal ions e.g. bismuth (III), antimony (III) and iron (III) from thiocyanate solutions. Bismuth and antimony were separated from concentrated acid medium (1–6 M H₂SO₄). Iron (III) was separated from pH 1 to 3. The kinetics of sorption of the Bi (III), Sb (III) and Fe (III) onto the Rod.B-PUF was found to be fast, the extraction is accomplished from 5 to 10 min with average values of half-life of sorption (t_1/2) of 2.9 min. The average values of the Gibbs free energy (ΔG) for the sorption of metal ions onto Rod.B-PUF are ?6.6 kJ mol^?1, which reflect the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Rod.B-PUF was also discussed.     

X-ray fluorescence spectrometric determination of germanium after extraction with polyurethane foam

Germanium is extracted onto polyurethane foam as molybdogermanate, and determined by X-ray fluorescence spectrometry in the dried foam. The extraction is effective between pH 0.5 and 3.7 and as little as 7 μg of germanium can be detected in 100 ml of aqueous solution.     

Gallium trace on-line preconcentration/separation and determination using a polyurethane foam mini-column and flame atomic absorption spectrometry. Application in aluminum alloys, natural waters and urine

A sensitive and selective flow injection time-based method for on-line preconcentration/separation and determination of gallium by flame atomic absorption spectrometry at trace levels was developed. The on-line formed gallium chloride complex is sorbed onto a polyether-type polyurethane foam mini-column, followed by on-line quantitative elution with isobutyl methyl ketone and direct introduction into the flame pneumatic nebulizer of the atomic absorption spectrometer. All chemical and flow variables of the system as well as the possible interferences were studied. The manner of strong HCl solutions propulsion was investigated and established using a combination of two displacement bottles. For 90 s preconcentration time, a sample frequency of 28 h⁻¹, an enhancement factor of 40, a detection limit of 6 μg l⁻¹ and a precision expressed as relative standard deviation (s_r) of 3.3% (at 1.00 mg l⁻¹) were achieved. The calibration curve is linear over the concentration range 0.02-3.00 mg l⁻¹. The accuracy of the developed method was sufficient and evaluated by the analysis of a silicon-aluminum alloy standard reference material. Finally, it was successfully applied to gallium determination in commercial aluminum alloys, natural waters and urine.     

Luminescence determination of europium microquantities after its preconcentration on polyurethane foam

Sorption of the mixed-ligand complexes of europium(III) with thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline (Phen) on polyurethane foam (PUF) has been studied by a luminescence method. The optimum conditions of sorption have been found. The sorbate composition on PUF has been determined (the Eu:TTA:Phen ratio was 1:3:1). Luminescence spectra of the europium complexes in solution and on PUF at 77 K have been investigated. It was concluded that the character of the Eu³⁺ coordination both in solution and on the sorbent is the same. Stability constants for the complexes in solution (lg K = 8.4) and on the sorbent (lg K = 5.5) have been calculated. The decrease of the stability of the complex on PUF is explained by the deformation of the complex molecule in the sorbent phase. Sorption coefficients for europium (245) and scandium (2.35) and the coefficient of selectivity for europium in Sc₂O₃ (102.3) have been determined. A method for the sorption-luminescence determination of europium in Sc₂O₃ with a lower limit of contents determined of 1 × 10⁻⁶⁰% has been developed.     

Preparation and properties of negative ion/polyurethane flexible foam composites

Abstract

In this study, negative ionpowder was modified with a silane coupling agent and then added to the polyurethane flexible foam to prepare NI/PU flexible foam composites by the one-step foaming method. The effects of the amount of negative ion powder on the mechanical properties, thermal properties and release of negative ions were investigated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and negative ion detectors. The SEM results showed that modified negative ion powder could be more uniformly distributed around the cell walls of the polyurethane flexible foam. The thermal stability, tensile strength and resilience of the NI/PU flexible foam composite were improved with the increase of the amount of modified negative ion powder. Increasing the amount of modified negative ion powder could also result in an increase in the release of negative ions, and it reached 5500/cm³ or higher at a negative ion content of 3%.     

Preconcentration and separation of acaricides by polyether based polyurethane foam

This paper reports the preconcentration of some dissolved organic phosphorous and chlorinated acaricides in water by porous polyether based polyurethane foam. Preliminary screening tests on the retention of the tested compounds, i.e., dicofol and bromopropylate, by polyether foams indicated that a very high percent removal of the tested species was obtained. The retention rate was found fast and reaches equilibrium in a few minutes. The various parameters, e.g., pH, extraction media, shaking time, salt effect, temperature and sample volumes affecting the preconcentration of the tested species by the unloaded foam, trioctylamine and trimethylphosphate treated foam have been optimized via batch modes of separation. The unloaded foams were employed in column modes for the retention and recovery of the tested species. The sorption efficiency and recovery of the compounds by the unloaded foams column were found to be up to 97.5%. The height equivalent to a theoretical plate (HETP) obtained by the unloaded foam was found to be in the range 1.1-1.3 ± 0.2 mm. The sorption mechanism of the tested compounds by the foams was discussed.     

Application of a new nanoporous sorbent for extraction and pre-concentration of lead and copper ions

The authors describe a method for the trace determination of copper (II) and lead (II) in water and fish samples using solid-phase extraction via siliceous mesocellular foam functionalised by dithizone. Siliceous mesocellular was functionalised with dithizone, and the resulting sorbent was characterised by scanning electron microscopy, surface area analysis, thermogravimetric/differential thermal analysis and FTIR. Following solid-phase extraction of target ions by the sorbent, copper and lead ions were quantified by flame atomic absorption spectrometry. Factors affecting the sorption and desorption of target ions by the sorbent were evaluated and optimised. The calibration plot is linear in the 1 – 500 μg L^?1 copper (II) and 3–700 μg L^?1 lead (II) concentration range. The relative recovery efficiency in real sample analysis is in the range from 96 to 102%, and precision varies between 1.7 and 2.8%. It is should be noted that the limits of detection for the copper and lead analysis were 0.8 and 1.6 μg L^?1, respectively. Also, the adsorption capacities for copper and lead ions were 120 and 160 mg g^?1, respectively. The obtained pre-concentration factor for the lead and copper ions by the proposed solid-phase extraction was 75. The method was successfully applied to the determination of low levels of copper (II) and lead (II) in tap, Caspian sea, Persian gulf and lake water and also their detection in fish samples.     

Preconcentration and separation of some organic water pollutants with polyurethane foam and activated carbon

Summary Although pesticides and phenols, cause reproductive failure in many areas of the world, there is a no effective means of treating waste water containing these compounds. This work deals with the adsorption of insecticides and phenols from aqueous solution by untreated porous polyurethane foam and activated carbon. Static experiments showed that in comparison with activated carbon a reasonable percentage of the compounds was adsorbed by the foam. Attempts were therefore made to extract these species from aqueous solution by foam column chromatography.The results showed that the adsorption of the compounds was brought about by a mechanism similar to that of solvent extraction. The effect of various experimental conditions such as temperature, extracting medium, pH, contact time, volume of sample flow rate, compound concentration, and eluting solvents on the retention and separation of the compounds has been determined. The height equivalent to a theoretical plate (HETP) was calculated from breakthrough capacity curves and from chromatograms obtained from polyurethane foam columns for the insecticide Dyfonate; values were in the range 2.1–2.3 mm at 10–15 ml min^–1. Extraction of the compounds from natural water, and subsequent recovery, were both found to be complete. The high capacity of polyurethane provides advantages over activated carbon; in particular, large sample volumes can be analyzed at high flow rates.     

Determination of Hg from Cu concentrates by X-ray fluorescence through preconcentration on polyurethane foam

A methodology was developed for the separation and determination of microamounts of mercury from copper concentrate samples by wavelength dispersive X-ray fluorescence (WDXRF) after solid-phase extraction of mercury from iodide medium using polyurethane foam (PUF). The best sorption conditions for the Hg-KI-PUF system were settled using X-ray fluorescence technique after collection of ground PUF on a filter paper by vacuum filtration and direct measurement of the intensity signal of the sorbed mercury on PUF. The main parameters of sorption such as iodide concentration, pH, shaking time and sample dilution effect were studied. The system shows rapid kinetic sorption and maximum X-ray intensity signal was achieved after shaking for 2 min a 0.01 mol l⁻¹ iodide solution containing microamounts of mercury in the pH range from 1.0 to 9.0. Effective sorption up to a volume of 0.9 l allows preconcentration of mercury. A linear fit up to 50 μg mercury was obtained by the plot of the initial mercury mass in the bulk solution (0.5 l) vs. its respective XRF intensity signal measurement on ground PUF after the sorption process. The calibration sensitivity, quantification and detection limits found were 9.09 CPS μg⁻¹, 9.0 and 2.7 μg, respectively. The sorption of many elements was also evaluated under the best conditions. High concentrations of Cu(II) and Fe(III) interfere seriously. Mercury-selective separation could be achieved using citrate or EDTA as masking agent; no interference due to copper matrix samples was observed in citrate medium. This methodology was evaluated by recovery for mercury determination in copper concentrate ore samples supplied by a mining industry and copper sulfate salts; the results were between 98% and 106%.     

Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam

A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0±0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l⁻¹, and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP–AES analysis.     

The determination of molybdenum in water and biological samples by graphite furnace atomic spectrometry after polyurethane foam column separation and preconcentration

A system for molybdenum separation and enrichment aiming its determination in water and biological samples by graphite furnace atomic absorption spectrometry (GFAAS) is proposed. The procedure is based on the sorption of the molybdenum (VI) thiocyanate complex onto a mini-column packed with polyurethane foam (PUF). The elution is accomplished by a 3.0 mol l⁻¹ nitric acid solution. Flow variables were optimized and an enrichment factor of 10 as well as a limit of detection (LOD) (3 s) of 0.08 μg l⁻¹ in the sample solution were achieved. The coefficient of variation showed values of 3 and 2% for molybdenum solutions of 2.0 and 10.0 μg l⁻¹, respectively. The accuracy of the method was confirmed by the good concordance between found and certified values in the analysis of certified reference materials (CRMs) (CASS-3 Nearshore Seawater, NIST 1547 Peach Leaves, NIST 1515 Apple Leaves and NIST 1572 Citrus Leaves). The procedure was also applied for the molybdenum determination in mineral waters as well as in produced water samples. The results obtained for the mineral water samples compared well with those obtained by ICP-MS. Concerning the produced water samples, in spite of their large salinity, recoveries of 90 to 120% at the 1 μg l⁻¹ were observed.     

Fabrication of nano-crystalline cellulose with phosphoric acid and its full application in a modified polyurethane foam

Nano-crystalline cellulose was fabricated in an anhydrous phosphoric acid system with medical absorbent cotton as its raw material. After ammonia neutralization, the whole system with produced phosphates and hydrolyzed saccharides was used as a modifier for preparing polyurethane foam (PUF). The NCC worked as a reinforce material, the phosphates served as flame-retardants, and the hydrolyzed saccharides partly replaced polyol. The addition of the modifier significantly improved mechanical property and flame-retardancy without an inferior thermal conductivity. When the dosage of modifier was 6% of the whole polyol, compressive strength increased 4.29 times, heat release rate dropped to 50.7%, and time to ignition extended to 2.6 times of those of the neat PUF. XRD and TEM analyses proved that the NCC in the modifier was rod-shape cellulose Ⅱ with diameter of 10 nm or so. FTIR analysis confirmed that the modifier well reacted with isocyanate, and SEM results revealed that the flame-retardant PUF had more uniform cells and more regular skeleton structure than the neat PUF.     

The chromatographic behavior of group (IIB) metal ions on polyurethane foam functionalized with 8-hydroxyquinoline

Polyurethane foam functionalized with 8-hydroxyquinoline has been prepared by coupling the foam matrix with 8-hydroxyquinoline (oxine) through an azo spacer. The oxine-bonded foam (Ox PUF) was characterized by use of different tools (UV–Vis spectra, IR spectra, density, and stability). Ox PUF was found to be very suitable for separation and preconcentration of trace metals, e.g. Zn(II), Cd(II), and Hg(II) ions, from wastewater in the pH ranges 2–12, 9–12, and 3–6, respectively. Various conditions influencing the sorption of these metal ions on to Ox PUF were optimized. Extraction of the metal ions was accomplished in 15 to 20 min. Study of the variation of the sorption of the tested metal ions with temperature yielded average values for H, S, and G of 41.99, 158.23, and –5.1 kJ mol^–1, respectively. The capacities of the foam material were 0.27, 0.16, and 0.09 mmol g^–1 for Zn(II), Cd(II), and Hg(II), respectively. Preconcentration factors >50 were achieved (RSD6.18). The quantitative results were obtained from experiments performed using certified reference materials.     

Ultrasonic-assisted leaching of trace metals from sediments as a function of pH

The effects of ultrasonication on the leaching of trace metals form sediments as a function of pH have been investigated using atomic absorption spectrometry. Cu, Pb, Ni, Zn and Mn were leached from sediments by ultrasonic effect using phthalate buffers at pH values of 2.2-6.0. Parameters influencing leaching, such as leaching time, solution matrix, wet or dry sample and final pH were evaluated. Results from ultrasonic leaching experiments were comparable to those of conventional procedure. In addition, this ultrasonic-assisted leaching method reduces the time required for conventional method approximately from 12 h to 25 min. Depending on the metal and sample type, metal removal increased linearly or exponentially with decreasing pH. The accuracy of the method was tested by comparing obtained results with this of conventional method. The average relative standard deviation (R.S.D.) of ultrasonic-assisted leaching method (ULM) varied between 1.71 and 3.00% for N = 36, depending on the analyte. This technique shows promise for studying chemical and biological availability and uptake/release processes for metals in sediment and soil as a function of pH.     

Preparation of novel ion exchange polyurethane foam and its application for separation and determination of palladium in environmental samples

The new strong anion exchanger (PUFIX) from polyurethane foam was prepared by coupling of the primary amine of the foam matrix with ethyl iodide. PUFIX was characterized using different tools (IR spectra, elemental analysis, density and thermal analysis). The sorption properties of the new anion exchanger (PUFIX) and chromatographic behaviour for separation and determination of palladium(II) ions at low concentrations from aqueous iodide or thiocyanate media were investigated by a batch and dynamic processes. The maximum sorption of Pd(II) was in the pH range of 0.3–2. The kinetics of sorption of the Pd(II) by the PUFIX was found to be fast with average values of half-life of sorption (t_1/2) of 3.32 min. The variation of the sorption of Pd(II) with temperature gives average values of ΔH, ΔS, ΔG and ΔE to be −38.3 kJ mol⁻¹, −100.7 J K⁻¹ mol⁻¹, −8.3 and 11.8 kJ mol⁻¹, respectively. The sorption capacity of PUFIX was 1.69 mmol g⁻¹ for Pd(II), preconcentration factors of values ≈250 and the recovery 99–100% were achieved (R.S.D. ≈ 1.24%). The lower detection limit, 1.28 ng mL⁻¹ was evaluated using spectrophotometric method (R.S.D. ≈ 2.46%).     

Determination of lead and cadmium in tap water and apple leaves after preconcentration on a new acetylacetone bonded polyurethane foam sorbent

The present work describes a rapid, cost-effective analytical procedure for the determination of lead and cadmium in environmental samples by off-line preconcentration with polyurethane foam (PUF) functionalised with acetylacetone by covalent coupling through the–N=N–group. The optimum pH ranges for quantitative uptake were 5–7, 6–7 for lead and cadmium, respectively. The kinetics of metal uptake by the new foam was found to be fast, reaching equilibrium in a few minutes. Metal ions were sorbed in the minicolumn, eluted with acid solutions and determined by flame atomic absorption spectrometer (FAAS). Under the optimum conditions, the preconcentration factors obtained were 288 for Cd and 224 for Pb. The limits of detection of the proposed procedure were 0.09 and 0.07 µg L^?1 for Pb and Cd, respectively. The relative standard deviation (RSD) was less than 10%. The accuracy of the method was estimated by using environmental samples that were spiked with Cd and Pb ions. The capacity of the acetylacetone bonded PUF (AA-BPUF) sorbent at optimum conditions has been found to be 4.5, 6.9 µmol g^?1 of sorbent for Pb and Cd, respectively.     

Preconcentration and separation of iron, zinc, cadmium and mercury, from waste water using Nile blue a grafted polyurethane foam

The present work describes a novel method for the incorporation of Nile blue A into polyurethane foam matrix. This foam material was found to be very suitable for the extraction of metal ions from aqueous solutions. The characterization of Nile blue A grafted foam and the effect of halide concentration, pH, shaking time, extraction isotherm and capacity have been investigated. This foam material was found to be suitable for the separation and preconcentration of iron (III), zinc (II), cadmium (II) and mercury (II) from waste water. The extraction was accomplished in (15-20) minutes. Iron was separated from acid medium (2-4 M HCl), zinc from (3-5 M HCl), cadmium from (4-6 M HCl) as thiocyanate complexes and mercury was separated from (1-2 M HCl) as chloride.     

Laboratory investigation of biodegradability of a polyurethane foam under anaerobic conditions

Polyurethane (PU) foams can be used in many remediation applications as an isolation material to prevent the release of hazardous materials into the environment. The integrity of a PU foam was investigated in this study using short-term accelerated laboratory experiments including bioavailability assays, soil burial experiments, and accelerated bioreactors to determine the fate of PU foam in the soil where anaerobic processes are dominant. The experimental results have shown that the studied PU foam is likely not biodegradable under anaerobic conditions. Neither weight loss nor a change in the tensile strength of the PU material after biological exposure was observed. The FT-IR chemical signature of the PU foams was also nearly identical before and after biological exposure. The composition of the PU material (aromatic polyester and polyether PU) used in this study could have played a significant role in its resistance to microbial attack during the short-term accelerated experiments.     

Bioprocess for solubilization of rock phosphate on starch based medium by Paecilomyces marquandii immobilized on polyurethane foam

Paecilomyces marquandii, a phosphate-solubilizing, starch-utilizing filamentous fungus, was immobilized on polyurethane foam (PUF). The immobilized fungus was applied in a repeated batch (six batches) fermentation process to solubilize Hirapur rock phosphate. The fungus was immobilized on PUF cubes and was used for phosphate solubilization in shake flask repeated batch cultivations. The fungus was also immobilized on PUF sheet and utilized in an airlift bioreactor in a repeated batch process. Maximum soluble phosphate (370 μg/ml) was recorded after third batch with 8 g rock phosphate/l. After 12 days of fermentation, a total production of 1,643 μg phosphate/ml was achieved.