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In this paper the combination of dispersive micro solid-phase extraction (DMSPE), using multiwalled carbon nanotubes (MWCNTs) as solid sorbents, with total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for preconcentration and determination of lead and cadmium ions in water samples. The proposed sample preparation is quite simple and economic. After the sorption processes of the metals on the MWCNTs, the aqueous sample is separated by centrifugation and the metal loaded MWCNTs are suspended using a small volume of an internal standard solution and analyzed directly by TXRF. Parameters affecting the extraction process (complexing agent, pH of the aqueous sample, amount of MWCNTs) and TXRF analysis (volume of the deposited suspension on the reflector, drying mode, and instrumental parameters) have been carefully evaluated to test the real capability of the developed methodology for the determination of Cd and Pb at trace levels. For both elements the linear range is observed up to 50 ng mL−1. Under optimized conditions detection limits are 1.0 ng mL−1 and 2.1 ng mL−1 for Cd(ii) and Pb(ii) ions, respectively. Both of the examined elements can be determined with quantitative recoveries (ca. 100%) and with an adequate precision (RSD = 6.0% and 10.5% for Cd(ii) and Pb(ii), respectively). Our results give insight into the possibilities of the combination of DMSPE and TXRF for trace metal determination in different types of environmental waters (sea, river and waste water). [ABSTRACT FROM AUTHOR]

The rapid development in nanomaterials and nanotechnologies has provided many new opportunities in the area related to analytical chemistry. In this paper the unique properties of these materials were used in order to preconcentrate heavy metals prior to detection by spectroscopic techniques. A novel, simple and highly reliable method for the preconcentration of trace amounts of chromium, manganese, cobalt, nickel, copper and zinc using electrochemically assisted sorption on oxidized multiwalled carbon nanotubes (MWCNTs) is developed. The proposed method is based on the application of an electric field to support the sorption process on oxidized MWCNTs. The proposed method was used to preconcentrate trace elements from water of pH = 4. After the preconcentration process, oxidized MWCNTs were directly measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer that reduces the number of chemicals required and minimizes sample handling. Besides EDXRF, any spectroscopy technique allowing the measurement of solid samples can be applied. The various parameters including pH of the solution, amounts of oxidized MWCNTs, sample volume and the influence of voltage as well as the time of assisted electric field on the sorption process were investigated for the optimization of the analytical procedure. Under optimized conditions the proposed preconcentration method offers a high recovery of 99% (Cr), 97% (Mn), 94% (Co), 96% (Ni), 92% (Cu) and 93% (Zn) and good precision of sample preparation (RSD) within 3.5–7%. If measurements are performed using the EDXRF spectrometer, the detection limits are 1 ng mL−1, 5 ng mL−1, 5 ng mL−1, 7 ng mL−1, 1 ng mL−1, 8 ng mL−1 for Cr(iii), Mn(ii), Co(ii), Ni(ii), Cu(ii) and Zn(ii), respectively. [ABSTRACT FROM AUTHOR]

Ultrasound-assisted solid-phase extraction (SPE) with multiwalled carbon nanotubes (MWCNTs) as a solid sorbent and 1-(2-pyridylazo)-2-naphthol (PAN) as a chelating agent was developed for the determination of trace and ultratrace amounts of Cd(ii) ions in aqueous samples. The solution containing Cd(ii) complexed with PAN was passed through the syringe filter with a PVDF membrane loaded with 25 mg of MWCNTs. The elution process was performed with 2.0 mL of 2.0 mol L−1 HNO3 with assistance of sonication. In order to obtain the high recovery of the Cd(ii) ions, the proposed procedure was optimized for various analytical parameters such as pH, amounts of PAN, sample volume, and elution conditions such as volume and concentration of eluent and influence of sonication and temperature. The investigation shows that sonication considerably improves the recovery, whereas temperature does not influence the elution process. Under optimized conditions Cd(ii) ions can be determined with very good recovery (99 ± 3%), precision (RSD = 3.2%) and detection limit (0.3 ng mL−1) for an enrichment factor of 50. The effect of common coexisting ions was also investigated. Cd(ii) can be determined in the presence of heavy metal ions and alkali metals. The proposed ultrasound-assisted SPE was applied for the determination of Cd(ii) in water samples and biological samples (Lobster Hepatopancreas). [ABSTRACT FROM AUTHOR]

A methodology based on dispersive micro solid-phase extraction (DMSPE) using multiwalled carbon nanotubes (MWCNTs) as solid sorbent prior to measurement with energy-dispersive X-ray fluorescence (EDXRF) spectrometry is proposed. The procedure consists of chelating of nickel, cobalt, copper, and lead ions with ammonium pyrrolidinedithiocarbamate (APDC) and posterior adsorption of metal chelates on MWCNTs (1 mg) dispersed in the aqueous samples (100 mL). DMSPE promotes immediate interaction between the metal chelates and MWCNTs and shortens time of sample preparation in comparison with classical solid-phase extraction. After microextraction process, MWCNTs are collected onto filter and directly measured by EDXRF. With this technique, the direct quantification of metal species held in solid materials is possible and, therefore, the elution step can be avoided. The effects of various experimental parameters such as pH of the solution, amounts of MWCNTs and APDC, sample volume, and time of stirring were investigated. With the best analytical conditions (1 mg of MWCNTs, 2 mg of APDC, 100 mL sample volume, pH = 7, and 5 min time of stirring), Co(II), Ni(II), Cu(II), and Pb(II) can be simultaneously determined with very good recoveries (101%, 98%, 96%, 99%, respectively) and detection limits (0.43, 0.11, 0.46, 0.15 ng mL−1, respectively). The method was applied in determination of trace metal ions in tap water and wastewater samples. [ABSTRACT FROM AUTHOR]

Abstract: The preconcentration of trace elements on multiwalled carbon nanotubes (MWCNTs) followed by a wavelength-dispersive X-ray fluorescence analysis (WDXRF) has been investigated. The proposed preconcentration procedure is based on the sorption of trace elements on MWCNTs dispersed in analyzed solution. After sorption, the MWCNTs with the metal ions were collected onto the filter, and then the preconcentrated elements were determined directly by WDXRF. The preconcentration method was optimized, and in consequence, in order to obtain satisfactory recoveries using 100mL of samples, the sorption process was performed with 1mg of MWCNTs within 5min. Some conditions of the preconcentration process such as the pH of analyte solution, amounts of MWCNTs, the volume of the sample, the contact time between analytes and MWCNTs (stirring time), and the effects of foreign metals are discussed in detail in the paper. Adsorption onto raw and oxidized MWCNTs was also studied. The proposed procedure allows obtaining the detection limits of 0.6, 0.6, 1.0, 0.7, 0.6, 0.5, 0.9 and 1.9ngmL−1 for Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II), respectively. The recoveries of determined elements were about 100%. Because the analytes are not eluted from the sorbent before WDXRF analysis, the risk of contamination and loss of analytes is reduced to minimum. Moreover, because the samples are analyzed as a thin layer, the matrix effects can be neglected. The proposed preconcentration method using MWCNTs coupled with WDXRF spectrometry was successfully applied to determine trace elements in natural water samples. [Copyright &y& Elsevier]