Juan M. Sanchez

The selective adsorption of gold (III) and palladium (II) on new phosphine sulphide-type chelating polymers bearing different spacer arms: Equilibrium and kinetic characterisation

Abstract New resins, with a functional group based on triisobutyl phosphine sulphide and containing different spacer arms between the polymeric matrix and the functional group, are evaluated in order to determine and characterise the mechanism of the metal adsorption process. These polymers are selective towards gold and palladium from other noble (Pt, Rh and Ir) and base (Fe, Cu, Ni and Zn) metals. Selectivity is higher in the case of gold (2.8 mmol Au/g resin for polymer 3 and 6.5 for polymer 4) than for palladium (0.5 mmol Pd/g resin for polymer 3 and 0.7 for polymer 4). The application of the Langmuir model to the data permits the determination of the adsorption mechanism, which we found to be a chelating process. The result shows that spacer heteroatoms become involved in the adsorption process. The kinetics of the adsorption is faster for palladium than for gold. The elution of these two metals is accomplished by the use of sodium nitrite and thiourea as eluting compounds.

Comparison of micellar and microemulsion electrokinetic chromatography for the analysis of water- and fat-soluble vitamins

Separation and determination of water- and fat-soluble vitamins by micellar (MEKC) and microemulsion electrokinetic chromatography (MEEKC) are compared. MEKC is only useful in the quantitative analysis of water-soluble vitamins when sodium dodecylsulfate (SDS) is used as the surfactant. However, the separation of mixtures containing water- and fat-soluble vitamins is only achieved by MEEKC using a microemulsion prepared by mixing SDS as the surfactant, butanol as the co-surfactant, octane as the non-polar modifier and propanol as the second co-surfactant. The injection time and the solvent used for the dilution of samples have a significant effect on the analysis of lypophilic compounds. The most reproducible results in the analysis of fat-soluble vitamins are obtained by using the same microemulsion electrolyte as the solvent for samples and an injection time of 10 s.

Headspace needle-trap analysis of priority volatile organic compounds from aqueous samples: Application to the analysis of natural and waste waters

Combining headspace (HS) sampling with a needle-trap device (NTD) to determine priority volatile organic compounds (VOCs) in water samples results in improved sensitivity and efficiency when compared to conventional static HS sampling. A 22 gauge stainless steel, 51-mm needle packed with Tenax TA and Carboxen 1000 particles is used as the NTD. Three different HS-NTD sampling methodologies are evaluated and all give limits of detection for the target VOCs in the ng L⁻¹ range. Active (purge-and-trap) HS-NTD sampling is found to give the best sensitivity but requires exhaustive control of the sampling conditions. The use of the NTD to collect the headspace gas sample results in a combined adsorption/desorption mechanism. The testing of different temperatures for the HS thermostating reveals a greater desorption effect when the sample is allowed to diffuse, whether passively or actively, through the sorbent particles. The limits of detection obtained in the simplest sampling methodology, static HS-NTD (5 mL aqueous sample in 20 mL HS vials, thermostating at 50 °C for 30 min with agitation), are sufficiently low as to permit its application to the analysis of 18 priority VOCs in natural and waste waters. In all cases compounds were detected below regulated levels.

New macroporous polymers for the selective adsorption of gold (III) and palladium (II). I. The synthesis, characterization, and effect of spacers on metal adsorption

New macroporous polymers with a functional group based on triisobutylphosphine sulphide are synthesized and characterized for the selective adsorption of gold and palladium. Five coordinating polymers are prepared from chloromethylated divinylbenzene polystyrene, by either direct attachement of the phosphine sulphide to the polymer or through a spacer chain that is modified to introduce O and S heteroatoms. The influence of the length and composition of the spacer chain on resin capacities is studied. The presence of O and S heteroatoms in the spacer increases the hydrophilicity of the polymers, and it is found to be essential for the adsorption of Au(III) and Pd(II). This is attributed to the coordination of the metal with the heteroatoms of the spacer.

Sorbent-packed needle microextraction trap for benzene, toluene, ethylbenzene, and xylenes determination in aqueous samples.

A needle trap (NT) device filled with Carbopack X as a sorbent material is evaluated for the static headspace analysis of benzene, toluene, ethylbenzene, and xylene (BTEX) compounds in aqueous samples. Injection parameters used with the NT device (e.g. volume of carrier gas and time to open the split valve) are evaluated to determine the mechanism involved during the desorption and transferring of the target compounds into the GC column. Furthermore, different parameters affecting the adsorption capacity of the sorbent are studied (e.g. sampling time and temperature, headspace/sample volume ratio, salting-out, and stirring). The evaluation of the method with aqueous samples shows that repeatability and recoveries with the NT device are equivalent to those obtained using solid-phase microextraction with a carboxen/PDMS (CAR/PDMS) coating. LODs obtained with flame ionization detection are in the range of 10-25 μg/L, and in the range of hundredths of μg/L with MS detection. The method developed is satisfactorily applied to the analysis of aqueous samples obtained from wastewater treatment plants.

Needle microextraction trap for on-site analysis of airborne volatile compounds at ultra-trace levels in gaseous samples.

Different capillary needle trap (NT) configurations are studied and compared to evaluate the suitability of this methodology for screening in the analysis of volatile organic compounds (VOCs) in air samples at ultra-trace levels. Totally, 22 gauge needles with side holes give the best performance and results, resulting in good sampling flow reproducibility as well as fast and complete NT conditioning and cleaning. Two different types of sorbent are evaluated: a graphitized carbon (Carbopack X) and a polymeric sorbent (Tenax TA). Optimized experimental conditions were desorption in the GC injector at 300°C, no make-up gas to help the transport of the desorbed compounds to the GC column, 1 min splitless time for injection/desorption, and leaving the NT in the hot injector for about 20 min. Cross-contamination is avoided when samples containing high VOC levels (above likely breakthrough values) are evaluated. Neither carryover nor contamination is detected for storage times up to 48 h at 4°C. The method developed is applied for the analysis of indoor air, outdoor air and breath samples. The results obtained are equivalent to those obtained with other thermal desorption devices but have the advantage of using small sample volumes, being simpler, more economical and more robust than conventional methodologies used for VOC analysis in air samples.

A Headspace needle-trap method for the analysis of volatile organic compounds in whole blood

Needle trap devices (NTDs) are a relatively new and promising tool for headspace (HS) analysis. In this study, a dynamic HS sampling procedure is evaluated for the determination of volatile organic compounds (VOCs) in whole blood samples. A full factorial design was used to evaluate the influence of the number of cycles and incubation time and it is demonstrated that the controlling factor in the process is the number of cycles. A mathematical model can be used to determine the most appropriate number of cycles required to adsorb a prefixed amount of VOCs present in the HS phase whenever quantitative adsorption is reached in each cycle. Matrix effect is of great importance when complex biological samples, such as blood, are analyzed. The evaluation of the salting out effect showed a significant improvement in the volatilization of VOCs to the HS in this type of matrices. Moreover, a 1:4 (blood:water) dilution is required to obtain quantitative recoveries of the target analytes when external calibration is used. The method developed gives detection limits in the 0.020-0.080μg L(-1) range (0.1-0.4μg L(-1) range for undiluted blood samples) with appropriate repeatability values (RSD<15% at high level and <23% at LOQ level). Figure of merits of the method can be improved by using a smaller phase ratio (i.e., an increase in the blood volume and a decrease in the HS volume), which lead to lower detection limits, better repeatability values and greater sensibility. Twenty-eight blood samples have been evaluated with the proposed method and the results agree with those indicated in other studies. Benzene was the only target compound that gave significant differences between blood levels detected in volunteer non-smokers and smokers.

Extraction of neodymium(III) at trace level with di(2-ethyl-hexyl)phosphoric acid in hexane

ABSTRACT The distribution of neodymium(III) between acidic aqueous nitrate solutions and organic solutions of di(2-ethyl-hexyl)phosphoric acid (D2EHPA) in hexane has been studied for different extractant and metal ratios at constant aqueous ionic strength 0.1 M (Na+,H+-NO3). The distribution data have been evaluated by both graphical and numerical analysis, in order to determine the speciation in the organic phase. The results obtained suggest the formation of two complexes in the organic phase: NdA3-3HA, which is predominant when the extractant/metal ratio is higher than one, and NdA3, which is the main species when the ratio is equal to one. For lower concentrations of extractant it has been found that the possible formation of species at the interface creates difficulties in the modelling of the extraction process.

A Comparison of the Separation Behavior of Some New Coordinating Resins and Commercial Quaternary Ammonium Resins with Reference to Their Separation of Gold(III) and Palladium(II) in Hydrochloric Acid Media

Abstract The adsorption and separation of gold(III) and palladium(II) chlorocomplexes by anion‐exchange and synthesized coordinating resins are evaluated and compared in batch and column operations. New coordinating resins with a functional group based on triisobutyl phosphine sulfide with spacer arms containing coordinating O and/or S atoms are used. For both types of resin, the mechanism of the metal adsorption process is characterized. The highest separation factors at equilibrium conditions are obtained with the coordinating resins. However, the adsorption rate is faster with the ion‐exchange resins. A faster kinetics of the adsorption process is obtained with both types of resin when the temperature is increased, but the total adsorption capacity increases at higher temperatures for the coordinating resins and decreases in the case of ion‐exchange resins. In column operations, the highest separation factors are obtained with the coordinating resin containing ethylene oxide chains as a spacer arm. The quantitative elution of both ions is achieved with all the resins, but it is only possible to obtain a 100% pure palladium fraction with the coordinating resins. These resins are also more selective than ion‐exchange resins, allowing the separation of palladium and gold chlorocomplexes from mixtures containing other noble and base metals.

Speciation of iridium(IV) in hydrochloric acid medium by means of capillary zone electrophoresis and spectrophotometry

Abstract Speciation of iridium(IV) [Ir(IV)] in hydrochloric acid solutions at different proton concentrations (between 1 and 10 −3 M ) has been studied using capillary zone electrophoresis and spectrophotometry in order to determine the number of species that are formed during the aquation and hydrolysis of the hexachloro complex of Ir(IV). The formation of more than seven species was found. The presence of [IrCl 6 ] 2− , [Ir(H 2 O)Cl 5 ] − and [Ir(OH)Cl 5 ] 2− species of Ir(IV) and [Ir(H 2 O)Cl 5 ] 2− and [Ir(OH)Cl 5 ] 3− of Ir(III) give the best explanation of the obtained results. The formation of other species detected in solution can be explained by the formation of dimers of the aquated species by the formation of hydroxo bridges. A spontaneous reduction of Ir(IV) to Ir(III) has been proved in all the solution studied. The extension of this process increases at higher pH values. Other peaks that appear in the electropherograms are associated to the formation of dimers of the aquated species by means of hydroxo bridges.