Enriqueta Anticó

Sensitive and stable monitoring of lead and cadmium in seawater using screen-printed electrode and electrochemical stripping analysis.

Sensitive and stable monitoring of heavy metals in seawater using screen-printed electrodes (SPE) is presented. The analytical performance of SPE coupled with square wave anodic stripping voltammetry (SWASV) for the simultaneous determination of Pb and Cd in seawater samples, in the low microgL(-1) range, is evaluated. The stripping response for the heavy metals following 2min deposition was linear over the concentration range examined (10-2000microgL(-1)) with detection limits of 1.8 and 2.9microgL(-1) for Pb and Cd, respectively. The accuracy of the method was validated by analyzing metal contents in different spiked seawater samples and comparing these results to those obtained with the well-established anodic stripping voltammetry using the hanging mercury drop electrode. Moreover, a certified reference material was also used and the results obtained were satisfactory.

Evaluation of an extraction method in the determination of the 2,4,6-trichloroanisole content of tainted cork

A method based on solvent extraction and GC-electron-capture detection analysis for the determination of 2,4,6-trichloroanisole (TCA) from cork has been evaluated and optimised. Our sample treatment consists of an extraction stage with pentane while the sample and solvent are kept in contact in a mechanical shaker (shake-flask extraction). Different extraction conditions have been tested in order to find the best compromise between efficiency and time of analysis. Different columns were evaluated for use in the concentration and purification step. A silica column was found to give the best performance in terms of recovery of TCA and repeatability. Pentane and mixtures of pentane-diethyl ether at different ratios were tested as eluting agents. It was found that 10 ml pentane allowed the recovery of retained TCA. Finally, the eluate was concentrated and injected into the chromatograph for TCA determination. The optimised chromatographic conditions enabled the quantification of TCA and 2,6-dichloroanisole, which was assayed as the internal standard. The shake-flask extraction method was compared with Soxhlet and ultrasound assisted extraction procedures using pentane as a solvent. Similar results were obtained for the shake-flask and Soxhlet extraction methods, while sonication gave significantly lower recoveries. The optimised shake-flask method was applied to determine the distribution of TCA in naturally contaminated cork bark.

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.

Solvent extraction of yttrium from chloride media by di (2- ethylhexyl) phosphoric acid in kerosene. Speciation studies and gel formation

Abstract The distribution of yttrium(III) between acidic aqueous chloride solutions and organic solutions of di(2-ethylhexyl) phosphoric acid, D2EHPA, in kerosene has been examined as a function of various chemical parameters at constant aqueous ionic strength 2.0 M and different ranges of metal concentration. For low and middle metal concentration, 1.5 × 10−4 − 2.587 × 10−2 M (13–2300mg l−1), the distribution of yttrium has been examined as a function of the extractant concentration and at fixed [H+] of 1.0M. The distribution data has been analyzed by both graphical and numerical methods. The results for the low metal concentration may be explained by the formation of two organic metal species, YA3.2HA and YA3.HA (HA refers to D2EHPA). Equilibrium constants have been determined and they are compared with corresponding constants in nitrate media and with results reported in the literature. Possible mixed extracted complexes containing chloride were rejected by the numerical calculations. Such prediction was confirmed by separate analysis of the chloride content in the organic phase. When the metal concentration is increased, the system shows a major complexity which is attributed to the formation of aggregates in the organic phase. For the highest metal concentration, a gel is observed to form under some of the experimental conditions. These results are discussed in terms of polymeric metal complexes.

Chemical pumping of rhodium by a supported liquid membrane containing Aliquat 336 as carrier

Abstract The mass transfer of Rh(III) from aqueous feed chloride solutions containing SCN − through a solid-supported liquid membrane (SSLM) consisting of Aliquat 336 dissolved in dodecane has been studied. The influence of hydrodynamic conditions as well as the chemical composition of the system on the permeation rate was investigated. Among the reagents tested as carriers, quaternary amines have been shown to be the most effective for the metal transport. Aliphatic organic diluents were chosen to avoid the degradation of the polymeric support, and 1-dodecanol was used as a modifier to increase the solubility of the extractant. The presence of thiocyanate in the feed solution was essential for the extraction of Rh(III). Furthermore, previous heating of the feed solution was necessary in order to form the extractable complex Rh(SCN) 6 3 . Different reducing compounds were tested as stripping agents, and 1.0 M NaHSO 3 solution was found to be the most effective to strip Rh(III) from the organic phase. Under these conditions, transport of Rh(III) through the membrane against its concentration gradient was achieved. The transport behavior of palladium and platinum in the proposed liquid membrane system was also studied. The obtained results reveal the possibility of exploiting the kinetic differences in the chemistry of the platinum group metals in the design of a process for the separation of these three metals.

Adsorption of palladium by glycolmethacrylate chelating resins

Abstract The adsorption of Pd(II) and Cu(II) on macroporous hydrophilic glycolmethacrylate gels with side chains containing 8-hydroxyquinoline (Spheron Oxine 1000), thiol (Spheron Thiol 1000) and salicyl groups (Spheron Salicyl 1000) has been investigated. Palladium is strongly adsorbed by Spheron Oxine and Spheron Thiol resins from a hydrochloric medium. The influence of pH and ionic strength has been determined. The elution of Pd(II) was carried out by using acidified thiourea or potassium thiocyanate solutions. Desorption was most effective for Spheron Oxine resin. The kinetics of metal adsorption by Spheron Oxine 1000 was also studied. The experimental data were analyzed numerically by considering both the forward and the reverse reaction, and corresponding constants are calculated for different initial metal and resin concentrations. Separation of aqueous mixtures of Pd(II) and Cu(II) by using Spheron Oxine is discussed.

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.

On-line determination of trace levels of palladium by flame atomic absorption spectrometry

A preconcentration method is developed for the on-line determination of palladium in complex matrices with flame atomic absorption spectrometry (FAAS). The flow system comprised of a minicolumn filled with polyamine Metalfix-Chelamine resin which is highly selective for Pt(IV), Au(III) and Pd(II). Best preconcentration conditions are established by testing different resin quantities, sample and eluent solution volumes, and adsorption and elution steps flow rates. Sample volumes of 4.7 ml of palladium solutions resulted in an enrichment factor of twenty at the optimum hydrodynamic conditions. This value can be increased by injecting larger volumes of sample solution. The method is sensitive, easy to operate and permitted the determination of sub-mg l(-1) levels of palladium with a detection limit of 0.009 mg l(-1). The resin was used up to 60 times in consecutive retention-elution cycles without any appreciable deterioration in its performance. The applicability of this method was tested by determining the palladium content in synthetic geological samples as well as in the pellet-type used car catalyst reference material.

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.

Monitoring Pb2+ with optical sensing films

Abstract A new lipophilic ionophore, N,N,N′,N′ -tetradodecyl-3,6-dioxaoctane-1-thio-8-oxodiamide (ETH 5493), is characterized in optical sensing films with a view to being used for environmental monitoring. It sufficiently discriminates all alkali and alkaline earth metal ions and, contrary to what is observed with the corresponding dithioamide, does not suffer from irreversible changes upon contact with Ag + and Hg 2+ salts. Different response functions are found for bulk optodes with ratios of chromoionophore/ion exchanger above and below 1.0. The data obtained fit the theoretical response function with a standard deviation of the residuals of 0.0012 absorbance units (AU) without any systematic error. When comparing different membranes, the precision is still high (±0.0029 AU) but the residuals show a certain systematic trend.