Cíntia S. Silva

Publications (4)6.07 Total impact

• Article: Direct determination of iron in sand using solid sampling graphite furnace atomic absorption spectrometry

  Cíntia S. Silva, Cassiana S. Nomura, Joaquim A. Nóbrega, Pedro V. Oliveira
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  ABSTRACT: A fast and reliable method for the direct determination of iron in sand by solid sampling graphite furnace atomic absorption spectrometry was developed. A Zeeman-effect 3-field background corrector was used to decrease the sensitivity of spectrometer measurements. This strategy allowed working with up to 200 µg of samples, thus improving the representativity. Using samples with small particle sizes (1–50 µm) and adding 5 µg Pd as chemical modifier, it was possible to obtain suitable calibration curves with aqueous reference solutions. The pyrolysis and atomization temperatures for the optimized heating program were 1400 and 2500 °C, respectively. The characteristic mass, based on integrated absorbance, was 56 pg, and the detection limits, calculated considering the variability of 20 consecutive measurements of platform inserted without sample was 32 pg. The accuracy of the procedure was checked with the analysis of two reference materials (IPT 62 and 63). The determined concentrations were in agreement with the recommended values (95% confidence level). Five sand samples were analyzed, and a good agreement (95% confidence level) was observed using the proposed method and conventional flame atomic absorption spectrometry. The relative standard deviations were lower than 25% (n = 5). The tube and boat platform lifetimes were around 1000 and 250 heating cycles, respectively.
  Microchimica Acta 03/2008; 161(1):109-114. · 3.03 Impact Factor
• Article: Electroanalysis of Crude Oil and Petroleum-Based Fuel for Trace Metals:  Evaluation of Different Microwave-Assisted Sample Decompositions and Stripping Techniques

  Rodrigo A. A. Munoz, Paulo R. M. Correia, Angerson N. Nascimento, Cíntia S. Silva, Pedro V. Oliveira, Lucio Angnes
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  ABSTRACT: Electroanalytical stripping techniques have been well-used for trace-metal determinations, because of their remarkable sensitivity and selectivity. However, when these techniques are applied for organic materials, such as crude oil and petroleum-based fuels, the samples must be decomposed. This paper evaluates the use of different microwave ovens for the decomposition of crude oil and diesel fuel to determine the content of copper, lead, mercury, and zinc in the digestates. A focused-microwave (FM) oven using H2SO4/HNO3/H2O2, operated at atmospheric pressure, and a closed-vessel microwave (CVM) oven using HNO3/H2O2, operated under pressure in a vessel, were evaluated. Square-wave stripping voltammetry (SWSV) and stripping chronopotentiometry (SCP) at gold film electrodes were applied for copper, lead, and mercury. Potentiometric stripping analysis (PSA) at mercury film electrodes was applied for copper, lead, and zinc. SWSV was more affected by residual organic matter, especially for lead determination. SCP presented higher sensitivity for copper and mercury at gold electrodes. PSA at mercury electrodes was preferred for lead and zinc determination. Better detection limits were attained for FM-digested solutions, after 0.8−1.0 g of sample can be digested, in contrast to the low quantities (0.10−0.25 g) used when pressurized vessels were explored. Nevertheless, the loss of mercury was verified when samples were decomposed in the FM oven.
  12/2006;
• Article: Potentiometric Stripping Analysis for Simultaneous Determination of Copper and Lead in Lubricating Oils After Total Digestion in a Focused Microwave-Assisted Oven

  Rodrigo A. A. Munoz, Cíntia S. Silva, Paulo R. M. Correia, Pedro V. Oliveira, Lúcio Angnes
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  ABSTRACT: The determination of metals in lubricating oil has been used as an important means of preventing components failures, to provide environmental information, and to solve criminal issues. In this study derivative potentiometric stripping analysis (DPSA) was used for the simultaneous determination of copper and lead in lubricating oils of vehicular engines. The samples were completely digested in a focused microwave-assisted oven using a powerful oxidant mixture (HNO3, H2SO4, H2O2). The optimized heating program to digest about 1mL of lubricating oil takes 45minutes. The residual carbon content after digestion was below 0.3%m/m for all samples. Copper and lead were also determined by graphite furnace atomic absorption spectrometry (GFAAS), and the results obtained were in good agreement with those obtained by electrochemical measurements. Recoveries of 94–109 and 93–103%, for copper and lead, respectively, were obtained for new and used lubricating oil samples.
  Microchimica Acta 03/2005; 149(3):199-204. · 3.03 Impact Factor
• Article: Bovine liver sample preparation and micro-homogeneity study for Cu and Zn determination by solid sampling electrothermal atomic absorption spectrometry

  Cassiana S. Nomura, Cíntia S. Silva, Ana R.A. Nogueira, Pedro V. Oliveira
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  ABSTRACT: This work describes a systematic study for the bovine liver sample preparation for Cu and Zn determination by solid sampling electrothermal atomic absorption spectrometry. The main parameters investigated were sample drying, grinding process, particle size, sample size, microsample homogeneity, and their relationship with the precision and accuracy of the method. A bovine liver sample was prepared using different drying procedures: (1) freeze drying, and (2) drying in a household microwave oven followed by drying in a stove at 60 °C until constant mass. Ball and cryogenic mills were used for grinding. Less sensitive wavelengths for Cu (216.5 nm) and Zn (307.6 nm), and Zeeman-based three-field background correction for Cu were used to diminish the sensitivities. The pyrolysis and atomization temperatures adopted were 1000 °C and 2300 °C for Cu, and 700 °C and 1700 °C for Zn, respectively. For both elements, it was possible to calibrate the spectrometer with aqueous solutions. The use of 250 μg of W + 200 μg of Rh as permanent chemical modifier was imperative for Zn. Under these conditions, the characteristic mass and detection limit were 1.4 ng and 1.6 ng for Cu, and 2.8 ng and 1.3 ng for Zn, respectively. The results showed good agreement (95% confidence level) for homogeneity of the entire material (> 200 mg) when the sample was dried in microwave/stove and ground in a cryogenic mill. The microsample homogeneity study showed that Zn is more dependent on the sample pretreatment than Cu. The bovine liver sample prepared in microwave/stove and ground in a cryogenic mill presented results with the lowest relative standard deviation for Cu than Zn. Good accuracy and precision were observed for bovine liver masses higher than 40 μg for Cu and 30 μg for Zn. The concentrations of Cu and Zn in the prepared bovine liver sample were 223 mg kg− 1 and 128 mg kg− 1, respectively. The relative standard deviations were lower than 6% (n = 5). The accuracy of the entire procedure was checked with bovine liver from NIST (1577b) and determination of Cu and Zn using flame atomic absorption spectrometry after microwave-assisted sample digestion.
  Spectrochimica Acta Part B: Atomic Spectroscopy.