Patricia Grinberg

Determination of copper, iron, lead and nickel in gasoline by electrothermal atomic absorption spectrometry using three-component solutions

Abstract An alternative procedure for the determination of copper, iron, lead and nickel in gasoline at μg l−1 levels, by graphite furnace atomic absorption spectrometry is described. The sample is stabilized by the formation of a three-component solution, prepared by mixing appropriate volumes of water, gasoline and n-propanol. This mixture resulted in a one-phase medium, which was indefinitely stable. No changes in the analyte signals were observed over several weeks, proving the ability of long-term stabilization. Appropriate calibration was achieved by using analytical solutions prepared in the same three-component medium or by the analyte addition technique. The palladium and magnesium nitrates modifier in aqueous solution proved to be efficient for iron and lead determination, while no modifier was necessary for copper and nickel. The characteristic masses in the three-component solution medium were 4.6, 18, 5.0 and 26 pg for copper, iron, nickel and lead, respectively. The detection limits (3s) for the whole analytical procedure were 0.4, 3.0, 0.8 and 1.8 μg l−1 for copper, iron, nickel and lead, respectively, in the original sample. Good agreement was observed between the results obtained by the proposed and comparative methods.

Some speculations on the mechanisms of photochemical vapor generation

Possible mechanisms are advanced to account for a number of observations/phenomena associated with the production of volatile metal species arising from photochemical vapor generation in acetic and formic acid media. These systems include mercury, iodine, selenium, iron and nickel as test cases which generate cold vapor, hydrides, methylated and carbonylated species. A model, based on the photochemical generation of free radicals involving ligand to metal charge transfer reductions and oxidations, is consistent with the majority of experimental data, including the identity of the resultant species and the impact of external parameters. This mechanistic framework will hopefully serve to enhance understanding of the technique so as to elicit enhanced performance through development of improved hardware and minimization/control of interferences.

A comparison of alkyl derivatization methods for speciation of mercury based on solid phase microextraction gas chromatography with furnace atomization plasma emission spectrometry detection

Several derivatizing agents were evaluated for use in speciating mercury in biological samples using solid phase microextraction in conjunction with tandem gas chromatography-furnace atomization plasma emission spectrometry (SPME-GC-FAPES). Following digestion with methanolic potassium hydroxide, the pH of the samples was adjusted and NaCl added when necessary. The mercury species were then derivatized with sodium tetraphenylborate or sodium tetrapropylborate and extracted by SPME using a 100 µm PDMS coated fiber. The derivatized species were then separated by GC and detected by FAPES. All experimental parameters were optimized for best separation and analytical response. Propylation proved to be more sensitive, robust and faster than ethylation or phenylation, leading to procedural detection limits of 0.55 ng g−1 for methylmercury, 0.34 ng g−1 for ethylmercury and 0.23 ng g−1 for inorganic mercury. An intra-day and intra-fiber precision of typically 2.2% was achieved whereas long-term (4 months) and inter-fiber reproducibility precision was typically 4.4%. The accuracy of the method was validated by the analysis of Certified Reference Materials (DORM-2, DOLT-2 and TORT-2) from the National Research Council of Canada.

Iridium as permanent modifier in the determination of lead in whole blood and urine by electrothermal atomic absorption spectrometry

Abstract The behavior of Iridium as a thermally deposited permanent modifier for the determination of lead by GFAAS was studied. The iridium coating procedure was optimized using a two-level factorial design. Using the optimized coating procedure, up to 1100 firings were possible with the same coating without sensitivity losses. The system was used in the determination of lead in whole blood and urine. A mixture of 0.1% Triton X-100 and 0.2% nitric acid was used as diluent. Pyrolysis temperature was 800°C for both matrices. Spiked, low-level samples were used for calibration. Under these conditions, no significant difference was found in comparison to the results obtained using a validated conventional modification procedure employing phosphate as modifier. Also, good agreement between found and certified/reference values were observed in the analysis of certified and commercial quality control materials, respectively. Such agreement was observed even using a 1100 times fired Ir coated platform–graphite tube assembly.

Simultaneous determination of Co, Fe, Ni and Pb in carbon nanotubes by means of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry

This work explores the possibilities of solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry for the direct analysis of carbon nanotubes. In particular, the simultaneous determination of Co, Fe, Ni and Pb is intended, as these elements are typically found in these samples as impurities. The results demonstrate that it is possible to find spectral (monitoring of the region between 283.168 and 283.481 nm), furnace (2500 °C for atomization; use of 100 ng Pd as a chemical modifier) and detector (use of side pixels to expand the linear range) conditions that permit the development of a fast and straightforward method for the simultaneous determination of the target elements at the levels at which they are typically found (mg g−1 for Co, Fe and Ni; μg g−1 for Pb) in carbon nanotubes. Limits of detection of 23 pg (Pb), 6 ng (Fe), 65 ng (Ni) and 86 ng (Co) were obtained, which are suitable for this type of sample. In this way, it was feasible to carry out the analysis of the samples investigated (one candidate reference material and three commercially available samples) and achieve accurate results when constructing the calibration curve with aqueous standards. Precision values for 5 solid sample replicates varied between 7 and 15% RSD in most cases. Overall, the proposed method shows important benefits for the cost-effective analysis of such complex samples in routine labs.

Determination of Trace Elements in Fluoropolymers after Microwave-Induced Combustion

An effective approach to the digestion of fluoropolymers for the determination of Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, and Ni impurities has been developed using microwave-induced combustion (MIC) in closed quartz vessels pressurized with oxygen. Samples that were examined included the following: polytetrafluorethylene (PTFE); polytetrafluoroethylene with an additional modifier, perfluoropropylvinylether (PTFE-TFM); and fluorinated ethylene propylene (FEP). A quartz device was used as a sample holder, and the influence of the absorber solution was evaluated. Determination of trace elements was performed by inductively coupled plasma-optical emission and mass spectrometry. Neutron activation analysis (NAA) was used for validation purposes. Results were also compared to those obtained using microwave-assisted acid extraction in high-pressure closed systems. Dilute nitric acid (5 mol L(-1)), which was selected as the absorbing medium, was used to reflux the sample for 5 min after the combustion. Using these conditions, agreement for all analytes was better than 98% when compared to values determined by NAA. The residual carbon content in the digests was lower than 1%, illustrating the high efficiency of the method. Up to 8 samples could be digested within 30 min using MIC, providing a suitable throughput, taking into account the inertness of such samples.

Photochemical vapor generation of iodine for detection by ICP-MS

A systematic evaluation of UV-photochemical generation of volatile iodine species for detection by ICP-MS is described. Several UV-based systems were studied, the most advantageous design being a modified cyclonic spray chamber fitted with a 6 W mercury pen lamp supplying 1 ml min−1 sample to a glass concentric nebulizer. Optimal conditions utilized a 5% v/v solution of acetic acid as the generation medium. The presence of the UV field enhanced signal intensity approximately 40-fold, providing a (blank limited) limit of detection of 0.7 pg ml−1127I+ and a precision of replicate measurement of 4% RSD at 10 ng ml−1 iodine. Using DRC technology and O2 as the reaction gas, suppression of 129Xe+ provided an estimated LOD of 6 fg ml −1129I+ in aqueous samples.

Generation of volatile cobalt species by UV photoreduction and their tentative identification

Generation of volatile cobalt carbonyl was accomplished by exposing a solution of inorganic cobalt, containing low molecular weight organic acids, to UV irradiation. The gaseous products were removed from the liquid phase in a gas–liquid separator and transported to a Pyrex U-tube cryogenic trap. Following cryocondensation of the products using a dry ice–acetone bath, the U-tube was placed in a hot water bath (35–40 °C) and the trapped species were introduced to an ICP-MS for estimation of the efficiency of generation. Alternatively, the gas phase containing the Co species was sampled with a gastight syringe and injected into a GC-MS for species identification. The product, which is stable for periods in excess of 60 minutes, is tentatively identified as a carbonylated cobalt species, generated with an efficiency of 0.3–0.4%

UV photochemical generation of volatile cadmium species

Photochemical generation of a volatile molecular Cd species from an acetic acid medium was accomplished using a thin film generator comprising a 20 W low pressure UV source. Argon gas was used to sweep the product vapor to a quartz tube atomizer heated to 900 °C. No signal was generated below about 770 °C and optimum atomization conditions required addition of 10% hydrogen to the Ar transfer gas, indicative of a thermochemical atomization process similar to that undergone for metal hydrides. UV generation efficiency exceeded 90% but the transfer of the analyte to the detector was problematic and precision of measurement was near 30% RSD. Despite such conditions, an estimated limit of detection was 2 μg l−1.

Determination of U, Th and Pu in natural waters, biological materials and clinical samples by ETV-ICP-MS

A method for the determination of U, Th and Pu in natural water, biological materials and urine samples by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) is described. Carbide formation was minimized using sample vaporization from a tantalum surface for U and additional use of tetrafluoromethane (Freon-23) as a gaseous modifier for Th and Pu. A prior Ca3(PO4)2 co-precipitation provided an enrichment factor of 50, yielding procedural detection limits (LOD) of 0.013, 0.029 and 0.017 pg g−1 for Th, U and Pu, respectively and corresponding absolute LODs of 0.13, 0.29 and 0.17 fg. Recovery of spikes from urine was typically 80%, whereas those from seawater, river water and biological materials averaged 99%. The accuracy of the method was validated by determination of U and Th in NIST SRM 1566b Oyster Tissue and U in a series of NRC natural water CRMs SLRS-4, CASS-4, NASS-5 and SLEW-3. Precision of determination was better than 10% at concentrations of 0.1 ng mL−1.