Ionic probes

AP has been used to probe micellar media (Saroja et al., 1998). The probe is located at the micellar interface and is well suited to monitoring micellar aggregation. In fact, the sharp change in the fluorescence intensity versus surfactant concentration allows the critical micellar concentration (CMC) to be determined. Excellent agreement with the literature values was found for anionic, cationic and nonionic surfactants. The electroneutrality of 4-AP and its small size are distinct advantages over ionic probes like ANS or TNS. 

Trivalent europium is an excellent ionic probe for materials and its luminescence properties are extensively studied. Eu is one of the mostly informative elements in mineralogy, especially when the ratio Eu /Eu may be assessed. Both oxidation states are luminescent, but the hnes of Eu in minerals are usually very weak and concealed by other centers. By steady state liuninescence spectroscopy its luminescence has been confidently detected only in scheehte and anhydrite (Tarashchan 1978 Gorobets and Rogojine 2001). 

L. L. M. Glavina and F. F. Cantwell, Origin of indirect detection in the liquid chromatography of a neutral sample with an ionic probe using an ODS bonded phase and aqueous mobile phase. Anal. Chem. 65 (1993), 268-276. 

In normal phase liquid chromatography, systems of this kind have been utilized to separate and monitor alkylammonium ions and dipeptides on columns containing naphthalenesulfonate in the stationary phase [3]. For carboxylic and sulfonic acids, dimethylprotriptyline has been used as the counter-ion [16]. Acetylcholine was isolated and measured as the picrate ion-pair in an extract from rat sciatic nerve [17], In reversed phase liquid chromatography, detection by the ion-pair technique has been performed via the presence of detectable ionic probe in the aqueous mobile phase. More recently this indirect detection method has developed very rapidly for organic ionized compounds, such as carboxylic acids, amines and amino acids [18, 19], and for inorganic anions [20, 21]. 

In the intermediate range of pH 10.4-7.0, the ESR lines of Af = 4-1 became asymmetric as a result of the overlapping of two lines, as shown in Figure 19.2. At a first glance, this peak asymmetry seems to be due to the coexistence of micelles and vesicles with the probe molecules distributed between them. Alternative explanations, however, would be that (i) two kinds of vesicles exist or (ii) that the carboxylic acid of 16-DS incorporated in the vesicles is partly dissociated and the ESR spectrum of the ionic probe (the carboxylate) differs from that of the nonionic one (the carboxylic acid). However, this latter possibility is unlikely as the line... 

Measurement with ionic probes yields an analogous result (ffeon instead of [Pg.413]

Somiyo A V, Gonzaiez-Serratos Y, Shuman H, McCieiian G and Somiyo A P 1981 Caicium reiease and ionic changes in the sarcopiasmatic reticuium of tetanized muscie an eiectron-probe study J. Oell Biol. 90 577-94... 

One of the most important advances in electrochemistry in the last decade was tlie application of STM and AFM to structural problems at the electrified solid/liquid interface [108. 109]. Sonnenfield and Hansma [110] were the first to use STM to study a surface innnersed in a liquid, thus extending STM beyond the gas/solid interfaces without a significant loss in resolution. In situ local-probe investigations at solid/liquid interfaces can be perfomied under electrochemical conditions if both phases are electronic and ionic conducting and this... 

In a series of papers published throughout the 1980s, Colin Poole and his co-workers investigated the solvation properties of a wide range of alkylammonium and, to a lesser extent, phosphonium salts. Parameters such as McReynolds phase constants were calculated by using the ionic liquids as stationary phases for gas chromatography and analysis of the retention of a variety of probe compounds. However, these analyses were found to be unsatisfactory and were abandoned in favour of an analysis that used Abraham s solvation parameter model [5]. 

To date, most studies of ionic liquids have used a small set of ionic liquids and have been based on the idea that, if the response of a particular probe molecule or reaction is like that in some known molecular solvent, then it can be said that the polarities of the ionic liquid and the molecular solvent are the same. This may not necessarily be the case. Only systematic investigations will show whether this is tme, and only when a wide range of ionic liquids with a wide range of different solvent polarity probes have been studied will we be able to make any truly general statements about the polarity of ionic liquids. Indeed, in our attempts to understand the nature of solvent effects in ionic liquids, we will probably have to refine our notion of polarity itself However, it is possible to draw some tentative general conclusions. 

Accordingly, the ionic conductivity in an electrolyte with negligible electronic conduction (/jon jtolal) may be determined by Ohm s law, provided that unpolarizable electrodes are employed. To overcome this limitation, separate voltage probes in the shape of identical electronic leads connected to the electrolyte at positions separated by a distance L may be employed (four-probe technique [38]). Under these... 

Potentiometry (discussed in Chapter 5), which is of great practical importance, is a static (zero current) technique in which the information about the sample composition is obtained from measurement of the potential established across a membrane. Different types of membrane materials, possessing different ion-recognition processes, have been developed to impart high selectivity. The resulting potentiometric probes have thus been widely used for several decades for direct monitoring of ionic species such as protons or calcium, fluoride, and potassium ions in complex samples. 

Figure 15. Complex plane impedance plots for polypyrrole at (A) 0.1, (B) -0.1, (C) -0.2, (D) -0.3, and (E) -0.4 V vs. Ag/AgCl in NaCl04(aq). The circled points are for a bare Pt electrode. Frequencies of selected points are marked in hertz. (Reprinted from X. Ren and P. O. Pickup, Impedance measurements of ionic conductivity as a probe of structure in electrochemi-cally deposited polypyrrole films, / Electmanal Chem. 396, 359-364, 1995, with kind permission from Elsevier Sciences S.A.)...

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