Edivaldo E. Garcia

Behaviour of arsenic and selenium in an ICP-QMS with collision and reaction interface

The performance of a collision reaction interface (CRI) for minimization of spectral interferences on analytical signals of 75As+ and 76Se+, 77Se+, 78Se+, 80Se+ and 82Se+ isotopes was evaluated by using H2 and He gases introduced through the sampler or skimmer cones of an inductively coupled plasma quadrupole mass spectrometer (ICP-QMS). Different gas flow rates were tested employing reference solutions prepared either in hydrochloric acid or in water soluble tertiary amines (CFA-C) media as carbon source. A hydrogen gas flow rate at 60 mL min−1 introduced through skimmer cone was effective for minimizing polyatomic interferences on 75As+ and Se isotopes, except for 80Se+. The use of He introduced through sampler or skimmer cones had a minor effect on the minimization of interferences when compared to the use of H2 gas. Moreover, it was observed that the gas introduction through the sampler cone had no effect on interferences when using gas flow rates up to 80 mL min−1 for both gases evaluated. Based on these results, it can be recommended to use H2 gas introduced through skimmer cone of the CRI for correcting polyatomic interferences on 75As+ and Se isotopes in matrixes containing up to 2% v v−1 chloride.

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 dysprosium and europium in sheep faeces by graphite furnace and tungsten coil electrothermal atomic absorption spectrometry

Tungsten coil atomizer atomic absorption spectrometry (TCAAS) was used to determine Dy and Eu in acid-digested faeces of sheep. These elements were used as markers in animal nutrition studies. Samples were dried, ground and decomposed using a nitric-perchloric acid mixture. The accuracy of the developed method was evaluated by graphite furnace atomic absorption spectrometry (GFAAS). The results obtained for Eu were validated at a 95% confidence level using a paired t-test. The results for Dy were not validated owing to memory effects caused by carbide formation into the graphite tube. This effect did not occur for Eu. The detection limits for Dy and Eu were 6.9 and 2.1 mug l(-1) by TCAAS, and 2.2 and 5.2 mug l(-1) by GFAAS, respectively. Relative standard deviations (R.S.D.; n=5) were 0.7-3.8 and 0.8-5.6% for Dy and Eu by TCAAS and 0.8-5.4 and 0.3-3.8% for Dy and Eu by GFAAS, respectively. The lifetime of the tungsten coil was around 200 heating cycles, which is three-fold higher than graphite tube lifetime. The proposed method can be used to determine the passage rate of feed through animal digestive tract.

A new strategy for preparation of hair slurries using cryogenic grinding and water-soluble tertiary-amines medium

Abstract The investigation of trace metal contents in hair can be used as an index of exposure to potentially toxic elements. Direct determination of Cd, Cu and Pb in slurries of hair samples was investigated using an atomic absorption spectrometer with Zeeman-effect background correction. The samples were pulverized in a freezer/mill for 13 min, and hair slurries with 1.0 g l −1 for the determination of Cu and Pb, and 5.0 g l −1 for the determination of Cd, respectively, were prepared in three different media: 0.1% v/v Triton X-100, 0.14 mol l −1 HNO 3 , and 0.1% v/v of CFA-C, a mixture of tertiary amines. The easiest way to manipulate the hair samples was in CFA-C medium. The optimum pyrolysis and atomization temperatures were established with hair sample slurries spiked with 10 μg l −1 Cd 2+ , 30 μg l −1 Pb 2+ , and 10 μg l −1 Cu 2+ . For Cd and Pb, Pd was used as a chemical modifier, and for Cu no modifier was needed. The analyte addition technique was used for quantification of Cd, Cu, and Pb in hair sample slurries. A reference material (GBW076901) was analyzed, and a paired t -test showed that the results for all elements obtained with the proposed slurry sampling procedure were in agreement at a 95% confidence level with the certified values. The cryogenic grinding was an effective strategy to efficiently pulverize hair samples.

Determination of sulfur in biodiesel microemulsions using the summation of the intensities of multiple emission lines

A method for the determination of sulfur in biodiesel samples by inductively coupled plasma optical emission spectrometry which uses microemulsion for sample preparation and the summation of the intensities of multiple emission lines has been developed. Microemulsions were prepared using 0.5 mL of 20% v/v HNO(3), 0.5 mL of Triton X-100, 2-3 mL of biodiesel sample, and diluted with n-propanol to a final volume of 10 mL. Summation of the emission intensities of multiple sulfur lines allowed for increased accuracy and sensitivity. The amounts of sulfur determined experimentally were between 2 and 7 mg L(-1), well below legislative standards for many countries. Recoveries obtained ranged from 72 to 119%, and recoveries obtained for the 182.562 nm line were slightly lower. This is most likely due to its lower sensitivity. Using microemulsion for sample preparation and the summation of the intensities of multiple emission lines for the successful determination of sulfur in biodiesel has been demonstrated.

Fractionation of aluminum in commercial green and roasted yerba mate samples (Ilex paraguariensis St. Hil.) and in their infusions.

Different trademarks of green mate and mate tea ( Ilex paraguariensis St. Hil.) were employed in this work, the aim of which was to compare the fractionation of Al from green mate and mate tea (roasted mate) and from their infusions. Using the flame atomic absorption spectrometry technique, contents determined for Al leached to green mate and mate tea infusions varied from 12.8 to 18.1% and from 5.9 to 10.6%, respectively. The concentrations of phenolics in infusions were determined using the Folin-Ciocalteu method, and the presence of melanoidins was also evaluated. The results showed that phenolic compounds are the major contributors to the leached Al in green mate infusions, but melanoidins also contribute in the case of infusions prepared from the mate tea. By employing a chelating resin batch procedure, it was observed that Al was predominantly in relatively inert forms, mainly in the case of mate tea infusions (50-70%).