Porphyrins in analytical chemistry. A review.

The application of metal-organic frameworks (MOFs) to anion separations with a special emphasis on anion selectivity is reviewed. The coordination frameworks are classified on the basis of the main interactions to the included anion, from weak and non-specific van der Waals forces to more specific interactions such as coordination to Lewis acid metal centers or hydrogen bonding. The importance of anion solvation phenomena to the observed anion selectivities is highlighted, and strategies for reversing the Hofmeister bias that favors large, less hydrophilic anions, and for obtaining peak selectivities based on shape recognition are delineated. Functionalization of the anion-binding sites in MOFs with strong and directional hydrogen-bonding groups that are complementary to the included anion, combined with organizational rigidity of the coordination framework, appears to be the most promising approach for achieving non-Hofmeister selectivity.

Anion Separation with Metal–Organic Frameworks

This article reviews recent advances in the field of potentiometric solvent polymeric membrane electrodes. These sensors have found widespread applications in a variety of fields, especially in the area of clinical diagnostics. Emphasis is given on the discussion of the theoretical and practical limits of ionophore-based ion-selective electrodes, with a special focus on electrode sensitivities, characterization of selectivities and dramatic improvements in detection limits. Advances in ionophore design and in the underlying model assumptions are also discussed. It is shown that a multitude of exciting new research possibilities have recently emerged in this well—established field.

Polymer Membrane Ion-Selective Electrodes–What are the Limits?

Nitrate-selective electrodes have been developed by electropolymerizing pyrrole onto glassy-carbon electrodes in the presence of NaNO 3 . Electrochemical variables were used to optimize the potentiometric response of the electrodes and to maximize the selectivity for nitrate over potentially interferent anions. Calibration plots with near-Nernstian slopes for nitrate were observed, -56±1 mV/decade (n=18), over a linear range of four decades of concentration (5.0×10 -5 -0.50 M nitrate). The electrodes had detection limits of (2±1)×10 -5 M nitrate (n=18). The commercially available nitrate-selective electrodes suffer from interference by lipophilic anions, such as perchlorate and iodide. Compared to these electrodes, the polypyrrole-based nitrate electrodes demonstrated improved selectivity coefficients for perchlorate and iodide by as much as 4 orders of magnitude (K pot NO3-,ClO4- =5.7×10 -2 , K pot NO3-,I- =5.1×10 -2 ). An electrochemically mediated templating mechanism is proposed to explain the observed high selectivity for nitrate

Nitrate-Selective Electrode Developed by Electrochemically Mediated Imprinting/Doping of Polypyrrole

Metallo-tetraazaporphyrin based anion sensors: regulation of sensor characteristics through central metal ion coordination

A new solvent polymeric membrane electrode based on Schitt base complexes of Co(II) is described which demonstrates excellent selectivity toward the iodide ion. The resulting electrode exhibits fairly low detection limits and good selectivity properties. The selectivity sequence observed is iodide>thiocyanate∼nitrite> perchlorate∼bromide>nitrate>chloride> sultate. The excellent selectivity for iodide is related to the unique interaction between the central Co(II) ion and iodide. The response mechanism of the electrode was also studied with the ac impedance and spectroscopic techniques

Schiff base complexes of cobalt(II) as neutral carriers for highly selective iodide electrodes

The anion-sensitive membrane electrodes based on lipophilic metalloporphyrin derivatives (FeTPP) 2 O show similar anti-Hofmeister selectivity sequence: SCN - >I - >ClO 4 - >NO 2 - >Br - >Cl - >NO 3 - . The electrode with an optimum membrane composition has a linear response for SCN - between 10 -6 and 10 -1 mol/L, with a slope of 53.0 mV/p-SCN - (25 o C). The origin of the anti-Hofmeister response characteristics has been discussed in view of the coordination chemistry of the metalloporphyrins. The interaction mechanism between (FeTPP) 2 O and SCN - is studies by UV/vis and IR spectroscopy

Metalloporphyrin Derivatives as Neutral Carriers for PVC Membrane Electrodes

PVC membrane electrodes based on cobalt phthalocyanine and its derivatives are described. An electrode that exhibits the selectivity sequence NO2– > SCN–≈ I–≫ CIO4– > Br– > NO3– > Cl– > OAc– was prepared. The electrodes show a linear response towards nitrite in the range 6 × 10–2–5 × 10–6 mol dm–3 with a slope of –52.0 mV decade–1(at 20 °C). The electrode has a satisfactory reproducibility and a rapid potential response. The UV spectra of the carrier and the a.c. impedance of the membrane were studied.

Jun-Zhong. Li

Papers

Schiff base complexes of cobalt(II) as neutral carriers for highly selective iodide electrodes

Metalloporphyrin Derivatives as Neutral Carriers for PVC Membrane Electrodes

Cobalt phthalocyanine derivatives as neutral carriers for nitrite-sensitive poly(vinyl chloride) membrane electrodes