Preparation of magnetic metal organic frameworks adsorbent modified with mercapto groups for the extraction and analysis of lead in food samples by flame atomic absorption spectrometry.

A novel magnetic metal organic frameworks adsorbent modified with mercapto groups was synthesized and developed for extraction and spectrophotometric determination of trace lead. The adsorbent was characterized by Fourier transforms infrared spectrometer, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The results indicated the adsorbents exhibited high adsorption capacities for lead due to the chelation mechanism between metal cations and mercapto groups. Meanwhile, the lead sorption onto the adsorbents could be easily separated from aqueous solution using a magnetic separation method. Under the optimal conditions, a linear calibration curve in the range from 1 to 20 µg L(-1) was achieved with an enrichment factor of 100. The limits of detection and quantitation for lead were found to be 0.29 and 0.97 µg L(-1), respectively. The developed method was successfully applied to the determination of trace amounts of lead in food samples and certified reference material with satisfactory results.

Carbon functionalized metal organic framework/Nafion composites as novel electrode materials for ultrasensitive determination of dopamine.

Carbon functionalized metal organic frameworks (C/Al-MIL-53-(OH)2) were successfully prepared for the first time by a solvothermal technique and characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectrometry, and scanning electron microscopy. This composite was coated with a Nafion film so as to form a Nafion/C/Al-MIL-53-(OH)2 modified glassy carbon electrode. The modified electrode was then used as a novel electrocatalyst for dopamine (DA) oxidation in phosphate buffer solution. Due to the synergistic effects of the different materials, including the high conductivity of carbon, the large surface area of Al-MIL-53-(OH)2, and the film-forming ability of a cation-exchange polymer, the modified electrode exhibited a remarkable enhancement effect on voltammetric response of DA. Under the optimal conditions, the response peak currents had a linear relationship with the DA concentration in the range from 3.0 × 10-8 to 1.0 × 10-5 mol L-1. The limits of detection and quantitation for DA were found to be 0.8 × 10-8 mol L-1 and 2.6 × 10-8 mol L-1, respectively. The analytical utilities of the proposed biosensor were achieved by analyzing the content of DA in biological fluids.

Metal-organic frameworks and ß-cyclodextrin-based composite electrode for simultaneous quantification of guanine and adenine in a lab-on-valve manifold.

In this work, a novel chemically modified electrode is constructed based on metal-organic frameworks and ß-cyclodextrin (Cu3(BTC)2/ß-CD, BTC = benzene-1,3,5-tricarboxylate) composite material. The electrode was used for simultaneous determination of guanine and adenine in a sequential injection lab-on-valve format and exhibited sensitive responses to guanine and adenine oxidation due to the π-π stacking interaction of Cu3(BTC)2 and the inclusion behavior of ß-CD. The analytical performance was assessed with respect to the supporting electrolyte and its pH, accumulation time and accumulation potential, and the fluid flow rates. Under optimal conditions, linear calibration ranges for both guanine and adenine were from 1.0 × 10(-7) to 1.0 × 10(-5) mol L(-1), and detection limits (S/N = 3) were found to be 5.2 × 10(-8) and 2.8 × 10(-8) mol L(-1), respectively. The proposed sensor showed advantages of high sensitivity, simple sample preparation protocol, enhanced throughput and good reproducibility. Finally, the practical application of the proposed sensor has been performed for the determination of guanine and adenine in real samples with satisfactory results.

Construction of an electrochemical sensor based on amino-functionalized metal-organic frameworks for differential pulse anodic stripping voltammetric determination of lead.

Metal-organic frameworks composite materials have received tremendous attention because of their versatile structures and tunable porosity for various applications. Herein, amino-functionalized metal-organic frameworks (NH2-Cu3(BTC)2; BTC=benzene-1,3,5-tricarboxylate) was prepared and used as a novel electrode modifier for the determination of trace levels of lead. NH2-Cu3(BTC)2 shows quite a good capability for the efficient adsorption of lead from aqueous solutions. The parameters affecting the electrochemical process, such as electrolyte solution pH, the amount of NH2-Cu3(BTC)2 suspension, accumulation potential and accumulation time, were investigated in detail. Under the optimal conditions, the electrochemical sensor exhibited a linear response to the concentration of lead in the range of 1.0×10(-8)-5.0×10(-7) mol L(-1) (R(2)=0.9951) with a detection limit of 5.0×10(-9) mol L(-1). The relative standard deviation of 11 successive scans was 3.10% for 1.0×10(-8) mol L(-1) lead. The method was validated with certified reference material (stream sediment and milk powder) and the analytical results coincided well with the certified values. Furthermore, the method was successfully applied to the determination of target analytes in tap and lake water samples and good recoveries were obtained from different spiked values.

Fabrication of metal-organic frameworks and graphite oxide hybrid composites for solid-phase extraction and preconcentration of luteolin.

A novel solid-phase extraction sorbent, metal-organic frameworks and graphite oxide hybrid composite, was prepared by a solvothermal technique. The morphology and properties of the resultant material were examined by Fourier transform infrared spectroscopy, X-ray diffraction and field emission scanning electron microscopy. To evaluate the extraction performance of the resultant sorbent, luteolin was chosen as a model analyte. The extraction conditions were optimized. Based on these, a convenient and efficient solid-phase extraction procedure for the determination of luteolin was established and the subsequent quantification step was performed by square wave anodic stripping voltammetry. Under the optimal conditions, the oxidation current increased linearly with increasing the concentration of luteolin in the range of 5.0 × 10(-9)-5.0 × 10(-7)molL(-1) with a correlation coefficient of 0.9983 and a detection limit of 7.9 × 10(-10)molL(-1). The relative standard deviation of seven successive scans was 4.20% for 5.0 × 10(-8)molL(-1) luteolin. This work not only proposes a useful method for sample pretreatment, but also reveals the great potential of metal-organic frameworks based hybrid materials as an excellent sorbent in solid-phase extraction.

Multi-walled carbon nanotubes and metal-organic framework nanocomposites as novel hybrid electrode materials for the determination of nano-molar levels of lead in a lab-on-valve format.

Metal-organic frameworks have been the subject of intense research because of their unique physicochemical properties. The presented study investigates the application of multi-wall carbon nanotubes and metal-organic frameworks (MWCNTs@Cu3(BTC)2) nanoparticles-modified electrode for the determination of trace levels of lead. The nanocomposites were prepared by solvothermal synthesis and characterized in detail. The experimental procedure was carried out by accumulating lead on the electrode surface and subsequently measuring with differential pulse anodic stripping voltammetry in a lab-on-valve format. The main parameters affecting the analytical performance, including the amount of MWCNTs@Cu3(BTC)2 suspension, supporting electrolyte and its pH, stripping mode, and flow rate, have been investigated in detail. Under the optimum conditions, the oxidation peak current displayed a calibration response for lead over a concentration range from 1.0 × 10(-9) to 5.0 × 10(-8) mol L(-1) with a excellent detection limit of 7.9 × 10(-10) mol L(-1). The relative standard deviation of 7 successive scans was 3.10% for 1.0 × 10(-8) mol L(-1) lead. The established method showed a great improvement in sensitivity and sample throughput for lead analysis.