Article pubs.acs.org/ac
Highly Ordered Binary Assembly of Silica Mesochannels and Surfactant Micelles for Extraction and Electrochemical Analysis of Trace Nitroaromatic Explosives and Pesticides Fei Yan,∥ Yayun He,∥ Longhua Ding, and Bin Su* Institute of Microanalytical Systems, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310058, China S Supporting Information *
ABSTRACT: The rapid and sensitive detection of nitroaromatic compounds is of great significance for human health, the environment, and public security. The present work reports on the extraction and electrochemical analysis of trace nitroaromatic compounds, such as explosives and organophosphate pesticides (OPs), using the indium tin oxide (ITO) electrodes modified with a highly ordered and aligned binary assembly of silica mesochannels and micelles (BASMM). With a pore diameter of ca. 2−3 nm, silica mesochannels (SMs) perpendicularly oriented to the ITO electrode surface can provide hard and robust supports to confine the soft cylindrical micelles formed by the aggregation of cationic surfactants, namely, cetyltrimethylammonium bromide (CTAB). Due to the organized self-assembly of hydrocarbon tails of CTAB surfactants, each micelle has a hydrophobic core, which acts as an excellent adsorbent for rapid extraction and preconcentration of trace nitroaromatic compounds from aqueous solutions via the hydrophobic effect. Furthermore, the cylindrical micelles are directly in contact with the underlying electrode surface, to which extracted compounds can freely diffuse and then be reduced therein, thus allowing their determination by means of voltammetry. Using the BASMM/ITO sensor, electrochemical analysis of trace nitroaromatic explosives, including 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol, 2,6-dinitrotoluene, 3-nitrophenol, and nitrobenzene, and OPs, such as paraoxon, methyl parathion, and fenitrothion, was achieved with a fast response, wide linear range, high sensitivity, and low detection limit at the ppb level. TNT and paraoxon in real apple, tea, and water samples were also determined. By combining the heterogeneous extraction and determination in one ordered binary nanostructure, the BASMM sensor provides a very simple, rapid, and cost-effective way for analysis of nitroaromatic compounds and can be extended to a wide range of lipophilic yet redox-active analytes.
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graphene,29,30 carbon nanotubes,31,32 cyclodextrin,18,33 molecularly printed polymer,34,35 and nanoparticles,36,37 is currently at the forefront of ultratrace electrochemical sensors for nitroaromatic explosives and OPs, because they exhibit effective enrichment performance to improve the sensitivity and the detection limit. Mesoporous silica materials have attracted considerable attention because of their robust nanostructure and many extraordinary properties including exceptional long-range order, controlled pore size, and high surface area.38−42 They are attractive as adsorbents and allow molecular diffusion.43−46 However, mesoporous silica materials usually have a low affinity for organics due to the high density of silanol groups on the surface. Therefore, surface modification of mesoporous silica to improve its hydrophobicity is often required. Compared to postsynthesis grafting by the addition of alkyl groups to the pore walls, as-synthesized mesoporous silica retaining surfactant micelles inside their pore channels has the advantages of controllability and ease of operation.47 Micelles are formed in
rowing interest has been aroused in the development of rapid, simple, low-cost, and sensitive methods for determination of ultratrace nitroaromatic compounds, such as explosives and organophosphate pesticides (OPs). The explosives, e.g., 2,4,6-trinitrotoluene (TNT), 2,6-dinitrotoluene (DNT), 2,4,6-trinitrophenol (TNP), 3-nitrophenol (NP), and nitrobenzene (NB) (see Scheme S1, Supporting Information), are of great concern with regard to public security and human health problems.1,2 OPs, e.g., paraoxon, parathion, and fenitrothion (see Scheme S2, Supporting Information), have been widely used for pest control in agriculture and are toxic and carcinogenic to human beings due to their serious bioaccumulation and persistence in the environment.3,4 So far, fluorescence,5−9 luminescence,10−13 electrochemistry,14−20 mass spectrometry,21,22 and capillary electrophoresis in connection with electrochemical detection23−25 have been widely employed for the detection of nitroaromatic compounds. Among them, electrochemical sensors have received considerable attention due to their high sensitivity, extended dynamic range, low cost, and convenient availability.26−28 The redox active properties of nitroaromatic explosives and OPs also make the electrochemical determination feasible and preferable. In addition, the use of nanomaterials, such as © 2015 American Chemical Society
Received: January 26, 2015 Accepted: March 27, 2015 Published: March 27, 2015 4436
DOI: 10.1021/acs.analchem.5b00433 Anal. Chem. 2015, 87, 4436−4441
Article
Analytical Chemistry
Scheme 1. Illustration of the Extraction and Electrochemical Analysis of Nitroaromatic Explosives and OPs at the BASMM/ITO Electrode
and potassium hydrogen phthalate (KHP) were ordered from Aladdin. TNP (1.00 mg/mL in acetonitrile) was obtained from J&K Chemicals. The stock solutions of explosives and OPs were prepared with methanol and ethanol, respectively, and stored at 4 °C for use. ITO coated glasses (surface resistivity
