Catarinie D. Pereira

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.

Biomonitoring of lead in Antarctic lichens using laser ablation inductively coupled plasma mass spectrometry

A method for direct determination of Pb by LA-ICP-MS in lichen samples collected in a heavily anthropogenically impacted area of Maritime Antarctica was developed. The lichen samples were cryogenically ground and digested with nitric acid and hydrogen peroxide. Lead determination by solution-based ICP-MS was validated by the use of 2 certified reference materials. Once the Pb concentrations were measured with adequate accuracy and precision, a method for its direct determination by LA-ICP-MS was developed. The laser ablation parameters were optimized by the use of a Doehlert design matrix. The final optimized conditions were: laser energy (60%), spot size (150 μm) and repetition rate (10 Hz). Lead concentration of the analyzed lichen samples were plotted against the intensity of the lead isotopes (208Pb, 207Pb and 206Pb) determined by LA-ICP-MS. Satisfactory linear correlation factors were obtained when 13C was used as internal standard. Lead distribution profiles in lichen thalli cross-sections were also obtained. By these results, LA-ICP-MS emerges as a potential analytical tool for Pb concentration estimation in lichen samples. Minimum amount of sample required, bioimaging capability, high analytical throughput, and minimization of waste generation are the major analytical features of this approach. The significant differences between the Pb concentration in the lichen samples from the control site (1.12 ± 0.05 mg kg−1) and from the impacted points (mean = 5.03 ± 0.57 mg kg−1) permitted qualify these organisms as good biomonitors. Elemental bioimaging of lichens demonstrated that the medulla region of lichen thalli is consistently the main atmospheric lead bioaccumulating lichen tissue.

Correction of matrix effects for As and Se in ICP OES using a Flow Blurring® multiple nebulizer

A new and efficient multiple nebulizer based on Flow Blurring® hydrodynamics (FBMN) has been employed for elemental analysis. The aerosol generated by the FBMN has been characterized and compared with a conventional pneumatic nebulizer (MicroMist®, MM). Both nebulizers have been operated with the same cyclonic spray chamber for comparison. At a solution flow rate of 300 μL min−1 and a nebulizer gas flow rate of 0.60 L min−1 the aerosol produced by the FBMN is formed by droplets smaller than 53 μm, and the Sauter mean diameter (D3,2) and the median diameter (D50) of the primary aerosols are 16.3 and 16.8 μm, and 20.4 and 23.3 μm with the FBMN and MM, respectively. The sample introduction system based on the FBMN successfully corrects matrix effects in As and Se determination by inductively coupled plasma optical emission spectrometry. The FBMN makes feasible the implementation of an on-line internal standard (I.S.) strategy by mixing the I.S. solution with analytical reference solutions or a sample solution directly in the spray chamber. It has been demonstrated that the combination of FBMN and In as an internal standard leads to better accuracy for determining As in a lake sediment.

Evaluation of a Collision-Reaction Interface (CRI) for Carbon Effect Correction on Chromium Determination in Environmental Samples by ICP-MS

Spectral interferences in inductively coupled plasma quadrupole mass spectrometry (ICP-MS) may affect several trace element analyses. In this work, the performance of a collision-reaction interface (CRI) for correction of spectral interferences on chromium determination at m/z 52 affected by 40Ar12C+ in a rich-carbon medium was evaluated. Hydrogen or He gases were introduced through sampler or skimmer cones of the CRI for promoting collisions and reactions. Background equivalent concentrations (BEC) and signal-background ratios (SBR) were the chosen parameters for evaluating CRI performance. It was observed that the introduction of both gases through the sampler cone was not effective considering the maximum gas flow rate evaluated at 140 mL min−1. The best condition to reduce polyatomic interferences caused by carbon containing species was obtained while introducing 60 mL min−1 of H2 through the skimmer cone. The trueness of the developed procedure was checked by 52Cr+ determination in certified reference materials. Sequential extractions in acetic acid and ammonium acetate (carbon sources) media, according to the Bureau Communautaire de Référence (BCR) of the Commission of the European Communities, was employed for BCR 701 (Lake Sediment) and microwave-assisted digestion was applied for Sewage Sludge from Industrial Origin (BCR 146 R). The feasibility of the CRI to overcome spectral interferences caused by molecular ions containing carbon on 52Cr+ determined by ICP-MS was demonstrated.