Study of carbon nanotubes and functionalized-carbon nanotubes as substrates for flow injection solid phase extraction associated to inductively coupled plasma with ultrasonic nebulization

A retrospective and prospective of the use of bio- and nanomaterials for preconcentration, speciation, and determination of trace elements: a review spanning 25 years of research

This review covers the investigations carried out with my colleagues and students during the last 25 years aimed at the development of analytical procedures for the preconcentration and/or speciation analysis of trace and ultra-trace elements using bio- and nanosorbents employing different methodologies, analytical techniques, and instrumental approaches. In the last years, an important part of this research was based on the use of nanomaterials for preconcentration and/or speciation studies. For their properties, they constitute a break point in the evolution of analytical chemistry. Special attention was paid to carbon nanotubes (CNTs) that resulted effective sorbents in flow systems using different immobilization strategies to improve their sorption capabilities. They resulted unique tools for on-line solid-phase (micro)extraction methods providing the appropriate selectivity (clean-up) and sensitivity (preconcentration) to reach the expected levels of many elements in matrices of biological or environmental interest. The performance of the different substrates, their strengths and weaknesses for the determination of trace elements, and their species in different matrices by a variety of analytical techniques are discussed in detail, along with perspectives and possible challenges in future development. This survey contains 96 references and covers primarily the literature published over the last 25 years by our research group. Relevant publications on the topics discussed were also included.

Restricted access carbon nanotubes for direct extraction of cadmium from human serum samples followed by atomic absorption spectrometry analysis

In this paper, we propose a new sorbent that is able to extract metal ions directly from untreated biological fluids, simultaneously excluding all proteins from these samples. The sorbent was obtained through the modification of carbon nanotubes (CNTs) with an external bovine serum albumin (BSA) layer, resulting in restricted access carbon nanotubes (RACNTs). The BSA layer was fixed through the interconnection between the amine groups of the BSA using glutaraldehyde as cross-linker. When a protein sample is percolated through a cartridge containing RACNTs and the sample pH is higher than the isoelectric point of the proteins, both proteins from the sample and the BSA layer are negatively ionized. Thus, an electrostatic repulsion prevents the interaction between the proteins from the sample on the RACNTs surface. At the same time, metal ions are adsorbed in the CNTs (core) after their passage through the chains of proteins. The Cd(2+) ion was selected for a proof-of-principle case to test the suitability of the RACNTs due to its toxicological relevance. RACNTs were able to extract Cd(2+) and exclude almost 100% of the proteins from the human serum samples in an online solid-phase extraction system coupled with thermospray flame furnace atomic absorption spectrometry. The limits of detection and quantification were 0.24 and 0.80 μg L(-1), respectively. The sampling frequency was 8.6h(-1), and the intra- and inter-day precisions at the 0.80, 15.0, and 30.0 μg L(-1) Cd(2+) levels were all lower than 10.1% (RSD). The recoveries obtained for human blood serum samples fortified with Cd(2+) ranged from 85.0% to 112.0%. The method was successfully applied to analyze Cd(2+) directly from six human blood serum samples without any pretreatment, and the observed concentrations ranged from <LOQ to 2.52 µg L(-1).

Grafting 3-mercaptopropyl trimethoxysilane on multi-walled carbon nanotubes surface for improving on-line cadmium(II) preconcentration from water samples

In the present study, the performance of multi-walled carbon nanotubes (MWCNTs) grafted with 3-mercaptopropyltrimethoxysilane (3-MPTMS), used as a solid phase extractor for Cd(2+) preconcentration in a flow injection system coupled to flame atomic absorption spectrometry (FAAS), was evaluated. The procedure involved the preconcentration of 20.0 mL of Cd(2+) solution at pH 7.5 (0.1 mol L(-1) buffer phosphate) through 70 mg of 3-MPTMS-grafted MWCNTs packed into a minicolumn at 6.0 mL min(-1). The elution step was carried out with 1.0 mol L(-1) HCl. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to estimate the extent of the MWCNT chemical modification. The 3-MPTMS-grafted MWCNTs provided a 1.68 times improvement in the sensitivity of the Cd(2+) FAAS determination compared to the unsilanized oxidized MWCNTs. The following parameters were obtained: preconcentration factor of 31.5, consumptive index of 0.635 mL, sample throughput of 14 h(-1), and concentration efficiency of 9.46 min(-1). The analytical curve was constructed in the range of 1.0-60.0 μg L(-1) (r=0.9988), and the detection and quantification limits were found to be 0.15 μg L(-1) and 0.62 μg L(-1), respectively. Different types of water samples and cigarette sample were successfully analyzed, and the results were compared using electrothermal atomic absorption spectrometry (ETAAS) as reference technique. In addition, the accuracy of proposed method was also checked by analysis of certified reference material NIST SRM 1573a (tomato leaves) and standard reference material NIST SRM 1643e (trace elements in natural waters).