This review focuses on the use of functionalized carbon nanotubes (CNTs) on the development of preconcentration methods with substantial contributions on selectivity and sensitivity for metal ions determination. CNTs have been usually employed in the development of preconcentration/speciation coupled to spectroanalytical techniques for ions determination at trace levels in different kind of samples. With regard the electroanalytical ones, this material has been widely used in adsorptive voltammetry procedures. Despite intrinsic features of CNTs, they suffer from poor dispersion in aqueous medium and wettability, thus making them very useful for sorption of hydrophobic metallic complex, but few indicated for metallic ions. Thus, different syntheses strategies, purification and chemical and physical approaches for surface functionalization/modification have been reported for improving the applicability of CNTs for a wide range of analytes. Therefore, apart from the brief description of the main physical and chemical characteristics of the carbon nanotubes, this review report the critical evaluation of main applications of modified CNTs as solid phase and as electrodic material for metal ions determination in environmental samples, food and biological using spectroanalytical techniques such as flame and graphite furnace atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry and electroanalytical mainly the adsorptive voltammetric ones.

Chemical imprinting technology has been widely used as a valuable tool in selective recognition of a given target analyte (molecule or metal ion), yielding a notable advance in the development of new analytical protocols. Since their discovery, molecularly imprinted polymers (MIPs) have been extensively studied with excellent reviews published. However, studies involving ion imprinted polymers (IIPs), in which metal ions are recognized in the presence of closely related inorganic ions, remain scarce. Thus, this review involved a survey of different synthetic approaches for preparing ion imprinted adsorbents and their application for the development of solid phase extraction methods, metal ion sensors (electrodes and optodes) and selective membranes.

The present work purposes the preparation of a silica gel sorbent organically modified with 2-aminoethyl-3-aminobutylmethyldimethoxysilane (AAMDMS) and imprinted with Cu2+ ions by means surface imprinting technique and its use for selective on-line sorbent preconcentration of Cu2+ ions with further UV-VIS spectrophotometric determination by flow injection analysis. The Cu2+-imprinted silica gel, when compared with non imprinted silica gel and silica gel, showed from the binary mixture of Cu2+/Ni2+ relative selectivity coefficient (k') of 6.84 and 5.43 and 6.64 and 19.83 for the mixture Cu2+/Pb2+, thus demonstrating higher selectivity of Cu2+-imprinted silica gel towards Cu2+ ions. Under optimized condition, the on-line preconcentration method provided detection limit of 3.4 μg L-1 and linear range ranging from 30.0 up to 300.0 μg L-1 (r = 0.995). The accuracy of method was successfully assessed by analyzing different kind of spiked water samples with recovery values ranging from 92.2 up to 103.0%.

Este estudo envolve a preparação de um polímero orgânico-inorgânico impresso com íon (IIP) para o enriquecimento seletivo de Ni2+ em soluções aquosas com posterior determinação por GF AAS. A rede polimérica híbrida foi preparada a partir de uma mistura do monômero funcional, 2-aminoetil-3-aminobutilmetildimetoxissilano e tetraetoxissilano como agente de ligação cruzada, contendo Ni2+ e brometo de cetiltrimetilamônio como moldes. Os polímeros foram caracterizados por IV, TG e MEV. A capacidade máxima adsortiva do IIP para os íons Ni2+, determinada pelo modelo linear de Langmuir, foi de 5,44 mg g-1. Quando o coeficiente de seletividade iônica do IIP foi comparado com os coeficientes de seletividade do NIP (non imprinted polymer) e IIP2 (ion imprinted polymer na ausência do surfactante), a partir das misturas binárias de Ni2+/Cu2+, Ni2+/Co2+, Ni2+/Cd2+ e Ni2+/Zn2+, os respectivos valores do coeficiente de seletividade relativo (k') foram 36,54 e 3,55, 1,22 e 2,03, 4,43 e 1,42, 28,60 e 1,74, demonstrando maior seletividade do IIP para os íons Ni2+. O método proposto forneceu um limite de detecção de 0,16 µg L-1 e foi aplicado com sucesso na determinação de Ni2+ em amostras de águas enriquecidas e fitoterápico (Gingko Biloba) com valores satisfatórios de recuperação.

This study involves the preparation of an ion imprinted organic-inorganic polymer (IIP) for selective sorbent enrichment of Ni2+ from aqueous solutions with further determination by GF AAS. The hybrid polymeric network was prepared from a mixture of 2-aminoethyl- 3-aminobutylmethyldimethoxysilane as functional monomer, and tetraethoxysilane as crosslinking agent, containing Ni2+ and cetyltrimethylammonium bromide as templates. The polymers were characterized by IR, TG and SEM. The maximum adsorptive capacity of IIP towards Ni2+ ions, determined by linear Langmuir model, was found to be 5.44 mg g-1. When the selectivity coefficient of IIP was compared with the selectivity coefficient of NIP (non imprinted polymer) and IIP2 (ion imprinted polymer in the absence of surfactant), from the binary mixtures of Ni2+/Cu2+, Ni2+/Co2+, Ni2+/Cd2+ and Ni2+/Zn2+, values of relative selectivity coefficient (k') were 36.54 and 3.55, 1.22 and 2.03, 4.43 and 1.42, 28.60 and 1.74, respectively, demonstrating higher selectivity of IIP for Ni2+ ions. The proposed method provided a limit of detection of 0.16 µg L-1 and was successfully applied for Ni2+ determination in spiked water samples and in a phytoterapic product (Gingko Biloba) with satisfactory recovery values.