Halide ion sensors

Many fluorescent molecular sensors for halide ions (except F ) are based on collisional quenching of a dye. In particular, the determination of chloride anions in living cells is done according to this principle. Examples of halide ion sensors are given in Figure 10.29. 

A. Galal, Z. Wang, A. E. Karagozler, H. Zimmer, H. B. Mark, Jr., and P. B. Bishop, A potentiometric halide ion sensor based on conducting polymer film electrode, II. Effect of electrode conditioning and technical specifications. Anal. Chim. Acta 299(2) 145 (1994). 

The design of fluorescent sensors is of major importance because of the high demand in analytical chemistry, clinical biochemistry, medicine, the environment, etc. Numerous chemical and biochemical analytes can be detected by fluorescence methods cations (H+, Li+, Na+, K+, Ca2+, Mg2+, Zn2+, Pb2+, Al3+, Cd2+, etc.), anions (halide ions, citrates, carboxylates, phosphates, ATP, etc.), neutral molecules (sugars, e.g. glucose, etc.) and gases (O2, CO2, NO, etc.). There is already a wide choice of fluorescent molecular sensors for particular applications and many of them are commercially available. However, there is still a need for sensors with improved selectivity and minimum perturbation of the microenvironment to be probed. Moreover, there is the potential for progress in the development of fluorescent sensors for biochemical analytes (amino acids, coenzymes, carbohydrates, nucleosides, nucleotides, etc.). 

In the method proposed by van Staden for the determination of three halides, these are separated in a short colunm packed with a strongly basic ion-exchange resin (Dowex i-X8) that is placed in an FI manifold. A laboratory-made tubular silver/silver halide ion-selective electrode is used as a potentiometric sensor. Van Staden compared the response capabilities of the halide-selective electrodes to a wide concentration range (20-5000 pg/mL) of individual and mixed halide solutions in the presence and absence of the ion-exchange column. By careful selection of appropriate concentrations of the potassixun nitrate carrier/eluent stream to satisfy the requirements of both the ion-exchange column and the halide-selective electrode, he succeeded in separating and determining chloride, bromide and iodide in mixed halide solutions with a detection limit of 5 /xg/mL [130]. 

Polyphenylene and polyfluorene have been extensively used as fluorescence-based sensors, and several chromogenic forms of these polymers have been reported. Incorporation of monomers with additional coordination sites into these polymers has led to the development of a variety of different anion sensors, mostly for halide ions (Lee et al. 2004 Zhou et al. 2005 Vetrichelvan et al. 2006 Kim et al. 2007). Extension of these materials toward recognition of more complex analytes should be possible. 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M" /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN", alkali metal ions, alkaline earth metal ions)... 

Nitrate in water may be analyzed by a nitrate selective sensor. Chloride and bicarbonate ions at concentrations about ten times greater than nitrate interfere in this test. Sulfide, cyanide, and halide ions are eliminated by using a buffer solution containing AgS04. The buffer — boric acid at pH 3 — removes bicarbonate. 

Another noteworthy example in which Cu(I) forms the basis of an optical anion sensor is 115, in which the metal complex acts both as a UV/vis signalling group and as a structural component dictating the topology of the urea anion-binding site [77]. The MLCT band within the Cu (phenanthroUne) complex at 282 nm is sensitive to halide ions, acetate and dihydrogenphosphate in 4 1 v/v THF/MeCN (a relatively low polarity solvent). However, in DMSO solution, only acetate and dihydrogenphosphate produced a UV/vis re-... 

In addition to halide ion conductors, proton conductors such as Nation membrane enabled the development of a unique amperometric oxygen sensor operating at ambient temperature. 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

Parker, D., Senanayake, P. K., Williams, J. A. G., Luminescent sensors for pH, p0(2), halide and hydroxide ions using phenanthridine as a photosensitiser in macrocyclic europium and terbium complexes. J. Chem. Soc., Perkin Trans. 21998, 2129-2139. 

One of the most important design changes in the evolution of this type of sensor was to produce complexes stable in aqueous media. The cyclen-based ligands and their stable Eu(III) and Tb(III) complexes, 44-46, represent examples of sensors developed by Parker et al. for pH, p02, halide and hydroxide ion sensing, [148-150]. The ligand used was based on cyclen substituted in one of the four positions with phenanthridine as the antenna and receptor. The other three positions were substituted with various pendant... 

---