Titanium dioxide nanotubes as solid-phase extraction adsorbent for on-line preconcentration and determination of trace rare earth elements by inductively coupled plasma mass spectrometry

doi:10.1016/j.microc.2013.02.010

Microchemical Journal

Volume 110, September 2013, Pages 89-93

https://doi.org/10.1016/j.microc.2013.02.010 Get rights and content

Highlights

•
Titanium dioxide nanotubes (TDNTs) were used as an adsorbent for preconcentration/separation of trace rare earth element.
•
TDNTs provide very attractive features such as large surface area, high chemical stability, non-toxicity and low cost.
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This method has the advantages of high adsorption capacity, low detection limit, good precision, sensitivity and accuracy.

Abstract

In this work, a novel method was developed for the determination of trace rare earth elements in biological and environmental samples by inductively coupled plasma mass spectrometry (ICP-MS) after on-line preconcentration/separation with a titanium dioxide nanotube packed microcolumn. The adsorption behaviors of the analytes on titanium dioxide nanotubes were studied systematically. The effects of the experimental parameters, including pH, sample solution flow rate and volume, eluent concentration and volume and interfering ions, on the recoveries of the analytes were examined in detail. Under the optimum conditions, the detection limits of this method ranged from 0.19 pg mL^− 1 (Lu) to 1.2 pg mL^− 1 (La) with an enrichment factor of 100, and the relative standard deviations (RSDs) for the determination of REEs were less than 5.0% (n = 9, c = 1.0 ng mL^− 1). The linear range of calibration curve spanned three orders of magnitude. This method was validated using a certified reference material of tea leaves, and successfully applied for the determination of trace light (La and Ce), medium (Eu and Gd) and heavy (Lu and Yb) rare earth elements in real samples with recoveries of 95.5–103%.

Introduction

It is well known that rare earth elements (REEs) have received an increasing amount of attention in high-technology fields ranging from superconductors, super-magnets, cathode-ray tubes, catalysts, diagnosis reagent of magnetic resonance imaging and laser materials to fertilizers in agriculture [1], [2], [3]. As a result, REEs are widely spread in the environment, and may enter the bodies of human beings via the food chain from environmental media such as water, soil and air [4], [5]. Several investigations have demonstrated that continuous exposure to REEs, even at a low concentration level, could cause adverse health effects. It was reported that long-term intake of low-dose REEs may lead to accumulation in the bone structure, changes in the bone tissue, and aberration of bone marrow cells and may even bring about the generation of genetic toxicity in bone marrow cells [6], [7], [8]. REEs can invade the central nervous system because they are susceptible to cerebral cortex and cause subclinical damage [9]. Therefore, the determination of trace REEs in biological and environmental samples has attracted considerable interest.

Inductively coupled plasma mass spectrometry (ICP-MS) has become one of the most appropriate techniques for the determination of trace/ultra-trace elements because of its excellent analytical features such as high sensitivity, low detection limit, wide linear range and rapid multi-elemental detection capability. ICP-MS, however, frequently suffers from problems with the effects of complicated matrices, including spectral interference and non-spectral interference. And sometimes it is quite difficult or even impossible to determine trace/ultra-trace elements at extremely low concentration levels directly by ICP-MS. In order to achieve an accurate and reliable analytical result, an efficient preconcentration and separation procedure is usually required prior to the determination. Up to date, a number of methods, including solvent extraction, coprecipitation, ion exchange, cloud point extraction, solid extraction, capillary microextraction and chromatography have been developed as pretreatment techniques to eliminate matrix interference and to preconcentrate trace elements for their determination by ICP-MS [10], [11], [12], [13], [14], [15], [16], [17]. Of the procedures mentioned above, solid-phase extraction (SPE) has received an increasing attention in the separation/preconcentration of trace elements and elimination of matrix interference because of (i) its high concentration factor, (ii) its simple operation, (iii) its ability to handle large volume samples in a closed system free from contamination, (iv) its rapid phase separation, and (v) the possibility of combining it with different analytical techniques [18], [19], [20]. It is worth noting that an adsorbent material plays a fundamentally crucial role in solid phase extraction technique to improve the analytical performance of a method. Thus, the development of a new adsorbent material with high selectivity and sensitivity is forever of interest to analysts.

In recent years, nanostructure material as a new adsorbent for the preconcentration/separation of substances has drawn growing attention in analytical sciences owing to its small size, large specific surface area, excellent mechanical strength, high chemical stability, and unique electrical properties. Some nanometer-sized substances have been successfully used as solid-phase extractants for preconcentration/separation of metal and nonmetal ions as well as adsorption of organic compounds [21], [22], [23], [24], [25], [26], [27], [28], [29]. Titanium dioxide nanotubes (TDNTs), as a new and excellent material, have attracted wide attention. It was proved that they have a larger surface area than titanium dioxide nanoparticles and carbon nanotubes [29], [30]. In addition, they provide very attractive features such as high chemical stability, durability, corrosion-resistance, non-toxicity and low cost. All of the facts mentioned above reveal to us that TDNTs may have a great analytical potential as an effective solid phase extraction adsorbent. To the best of our knowledge, however, there have been very few reports on this topic so far [31].

The purpose of this work is to investigate the feasibility of TDNTs as SPE adsorbents for the preconcentration and determination of trace REEs. On the basis of the experimental results obtained, a novel method using a microcolumn packed with TDNTs coupled with inductively coupled plasma mass spectrometry (ICP-MS) was developed for in-line and simultaneous determination of the trace REEs (La, Ce, Eu, Gd, Lu and Yb) in biological and environmental samples.

Section snippets

Instrumentation

An X-7 ICP-MS system (Thermo Elemental Corporation, USA) was used for the determination of REEs. The optimum operating conditions for ICP-MS are summarized in Table 1. The ion lens settings, nebulizer flow rate, and torch position of the instrument were optimized daily in order to obtain the maximum ¹¹⁵In count rate.

A HL-2 peristaltic pump (Shanghai Qingpu Huxi Instrument Factory, China) coupled with a self-made polytetrafluoroethylene (PTFE) microcolumn (20 mm × 3.0 mm id), packed with TDNTs, was

Effect of pH on adsorption

In this work, the pH value plays an essential role with respect to the adsorption of analytes on TDNTs, since it affects the surface charge and speciation of the adsorbent. Thus, the effect of pH on the retention of analytes on the column of TDNTs was studied. The sample solutions were adjusted to a pH range of 1.0–9.0 with HNO₃ and NH₃·H₂O, and then passed through the microcolumn. The retained ions were stripped off from the column, and measured by ICP-MS as described in the recommended

Conclusions

In this work, titanium dioxide nanotubes (TDNTs) were used as solid phase extractor for in-line preconcentration/separation and determination of trace/ultra-trace rare earth elements (REEs) in biological and environmental samples by ICP-MS. The adsorption behavior of REEs on TDNTs was investigated systematically. The analytes can be retained on TDNTs in the pH range of 7.0–9.0, desorbed quantitatively with 2 mL of 1.0 mol L^− 1 HNO₃, and no carryover is observed in the next analysis. An enrichment

Acknowledgments

Financial support from the Nature Science Foundation and the Education Department Foundation of Hubei Province in China is gratefully acknowledged.

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Titanium dioxide nanotubes as solid-phase extraction adsorbent for on-line preconcentration and determination of trace rare earth elements by inductively coupled plasma mass spectrometry

Highlights

Abstract

Introduction

Section snippets

Instrumentation

Effect of pH on adsorption

Conclusions

Acknowledgments

Environ. Pollut.

Microchem. J.

Microchem. J.

Anal. Chim. Acta

Anal. Chim. Acta

Microchem. J.

Anal. Chim. Acta

Spectrochim. Acta B

Microchem. J.

At. Spectrosc.

Microchem. J.

Microchem. J.

Anal. Chim. Acta

Talanta

Determination of trace level lanthanides and thorium by inductively coupled plasma atomic emission spectrometry in different types of geological, red mud, and coal fly ash samples after separation as oxalates using calcium as carrier

At. Spectrosc.

Effect of agricultural use of phosphogypsum on trace elements in soils and vegetation

Sci. Total. Environ.