Quantification of ytterbium in road dust applying slurry sampling and detection by high-resolution continuum source graphite furnace atomic absorption spectrometry

https://doi.org/10.1016/j.sab.2020.105938Get rights and content

Highlights

  • Determination of Yb in road dust sample by HR-CS-GFAAS is first reported.

  • Tungsten as permanent chemical modifier was effective in eliminating memory effects.

  • Doehlert design was used to optimize the slurry preparation of road dust.

  • Slurry sampling was advantageous compared to acid digestion for Yb determination.

Abstract

In this work, the determination of ytterbium in road dust samples, employing a simple and fast methodology, based on sample preparation as slurry and analysis by high resolution-continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS), is purposed. The determinations were carried out on the Yb main line, 398.799 nm, using an integration time of 5.0 s. The optimum condition for the slurry preparation of road dust samples was established through a Doehlert matrix for two variables, which employed a HNO3 concentration of 0.24 mol L−1 and homogenization time of 34 min, using ultrasonic bath. The temperatures applied to the graphite furnace were optimized, wherein the pyrolysis and atomization temperatures were 1200 °C and 2700 °C, respectively, using 250 μg of W as permanent chemical modifier. To investigate possible matrix interferences in the determination of Yb in road dust samples, external calibration and standard addition curves were compared. The comparison between slopes of the external and standard addition calibration curves showed difference of about 7.0%, an indication of absence of matrix effects for determination of Yb in road dust samples. The limit of detection (LOD) and limit of quantification (LOQ) were 22 and 72 ng g−1, respectively, with a characteristic mass of 6.0 pg. The accuracy was confirmed through analyses of three certified reference materials (CRM): Trace Elements in Soil Containing Lead From Paint (NIST 2586), Rock (NCS DC 73301) and Geochemical Soil (TILL-1), and the good agreement between the found and certified values was obtained, 99 ± 4 to 104 ± 2%, corroborating the accuracy of the analytical method. The precision was expressed as relative standard deviation (RSD) for measurements in triplicate, being lower than or equal to 10.0%. The analytical method was used for Yb determination in eight samples of dust collected in an urban area of Salvador and Jaguaquara, Bahia State, Northeast, Brazil. The concentrations obtained for Yb ranged from 172 ± 13 to 2065 ± 122 ng g−1. Thus, the proposed analytical method presents the characteristics of being fast, precise and accurate for the determination of Yb in road dust samples, employing slurry sampling and detection by HR-CS-GFAAS.

Introduction

Ytterbium is one of the so-called “rare earth elements” (REE), which corresponds to the series of lanthanides plus scandium and yttrium [[1], [2], [3]]. As other REE's, ytterbium has arisen great interest and economic concern, as it plays a crucial role for the high-tech industry. The field of its application is vast, due to its unique physical and chemical properties, it has been widely used in various types of industrial products, such as lasers, optical fiber, solar panels, catalysts, among other products of high technology [[4], [5], [6]].

The interest in REE has increased global demand, and consequently an interest in the anthropogenic contribution, which may affect the distribution pattern of ytterbium, bringing risks to the environment and the human health [7]. In this sense, ytterbium-containing compounds can be potentially hazardous due to their toxicological effects, such as irritation of the skin and eyes, and possibly it is teratogenic, being able to cause damage to the structure of the embryo or fetus during pregnancy [8,9].

In view of this environmental problem, the determination of ytterbium in environmental matrices, such as road dust is necessary to assess the risks inherent to the environment and human health, but its determination is not trivial due to the low concentrations of Yb and the concomitant elements present in high concentrations in this matrix [[10], [11], [12]].

For determination of Yb in road dust, the presence of refractory silicates and aluminates, in the chemical composition of the sample, requires the use of a mixture of complexing acids (such as HF and HCl), besides oxidants acids (HNO3 and HClO4), in the preparation step. However, the use of HClO4 makes the procedure dangerous, due to the risk of explosions, and the use of HF, which can cause severe burns, promotes the formation of Yb fluoride, requiring the use of boric acid to complex the fluoride and release the analyte into the solution [[13], [14], [15], [16]].

Problems related to the sample preparation of road dust, containing high content of silicates, do not stop only in acid digestion, sample treatment through alkaline fusion, which has been considered an alternative procedure, also presents some disadvantages, such as greater consumption of reagents and high dilution factor of the sample, making it difficult the determination of ytterbium by low sensitive spectroanalytical techniques [17].

According to reports in literature, inductively coupled plasma optical emission spectrometry (ICP-OES), a simultaneous multi-element technique with a wide concentration range, presents low sensitivity and spectral interferences for determination of Yb. On the other hand, inductively coupled plasma mass spectrometry (ICP-MS) is suitable for determining Yb, due to its high sensitivity, precision, fastness, lower detection limit than ICP-OES, and a wide dynamic linear range. However, when it comes to the determination of REEs, there is evidence of important isobaric interferences, with the spectral overlap of light REE oxides (low mass) on heavy REE (high mass) [18,19].

The analysis of the sample in the form of slurry and detection by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS) is effective when compared to methods based on inductively coupled plasma (ICP), mainly due to a pyrolysis step, which removes the components of the matrix before the atomization step, and the lower probability of obstruction of the sample introduction system [[20], [21], [22], [23]]. An additional advantage of HR-CS-GFAAS is the ability of background correction and visualization of the entire spectral environment in the vicinity of the analytical line, especially for samples presenting excessive background due to a relatively large amount of matrix within the graphite furnace, as for example sewage sludge sample [21,24,25].

Slurry sampling provides advantages that contribute to analysis by HR-CS-GFAAS. Slurry is a dispersion of solid in a liquid phase, it can be easily injected as solution in the graphite furnace, enabling the direct determination of the analyte, demanding a short time for preparation and mitigating contamination risks, when compared to acid decomposition methods [20,21,26].

However, some problems can occur in HR-CS-GFAAS, as well as, in other techniques such as electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) and graphite furnace atomic absorption spectrometry (GF AAS): high atomization or vaporization temperature, a longer integration time, severe memory effect due to the formation of stable REE carbides and reduction in the graphite furnace lifetime [[27], [28], [29]]. Goltz et al. [29] reported the use of W as permanent chemical modifier to attenuate the memory effect in the determination of REE by ETV-ICP-MS. Shizhong et al. [30] reported the use of 1-(2′-pyridylazo)-2-naphthol as chemical modifier to promote the formation of volatile oxides for the determination of Yb by ETV-ICP-OES at low vaporization temperature. The summary of the different analytical methods for determination of REE were reviewed by several authors [18,31,32].

In this context, this work aims to optimize a simple and fast analytical method on laboratory routine for determination of Yb in road dust sample using preparation in the form of slurry and detection by HR-CS-GFAAS, avoiding sample dissolution and the use of harmful reagents.

Section snippets

Instrumentation

An analytical balance (model AG 285, Mettler Toledo, Greifensee, Switzerland) was employed to weigh the sample masses. An ultrasonic bath (model EASY 30H, Elma, Hohentwiel, Germany) was used to prepare the samples in the form of slurries in 15 mL polypropylene tubes (Sarstedt, Newton, NC, USA). A microwave oven (Mars 6 OneTouch, CEM, Matthews, USA) was used for microwave-assisted sample digestion, as a comparative procedure of the road dust sample preparation.

The measurements were carried out

Investigation of pyrolysis and atomization temperature curves for determination of Yb

To obtain the pyrolysis and atomization temperature curves, the sample coded as 1-CS was used. Pyrolysis and atomization temperature curves were obtained as follows: (i) only with sample 1-CS; (ii) only with the standard solution of Yb 10 μg L−1 (mass: 200 pg); (iii) with a standard solution of Yb 10 μg L−1 (mass: 200 pg) in the presence of 10 μL of Pd 1000 μg mL−1 (mass: 10 μg Pd); (iv) with standard solution of Yb 10 μg L−1 (mass: 200 pg) in the presence of 250 μg W, thermally deposited in

Conclusions

The proposed methodology proved to be fast, precise, accurate and simple for determination of Yb in road dust samples by HR-CS-GFAAS. Among the main advantages of the proposed procedure, the use of slurry sampling, for the determination of rare earth elements, is easy to handle and low cost when compared to conventional methods of sample preparation (microwave-assisted digestion), which include the use of concentrated mineral acids, such as HF.

The use of 10 μg W as permanent chemical modifier

Acknowledgments

The authors are grateful for the infrastructure, scholarships and financial resources for research provided by the Fundação de Amparo à Pesquisa do Estado da Bahia (FAPESB, Salvador, Brazil) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brasília, Brazil). This study was also financed in part by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES, Brasília, Brazil) – Finance Code 001.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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