Rubidium electrode

A suitable extrathermodynamic approach is based on structural considerations. The oldest assumption of this type was based on the properties of the rubidium(I) ion, which has a large radius but low deformability. V. A. Pleskov assumed that its solvation energy is the same in all solvents, so that the Galvani potential difference for the rubidium electrode (cf. Eq. 3.1.21) is a constant independent of the solvent. A further assumption was the independence of the standard Galvani potential of the ferricinium-ferrocene redox system (H. Strehlow) or the bis-diphenyl chromium(II)-bis-diphenyl chromium(I) redox system (A. Rusina and G. Gritzner) of the medium. 

The following table lists some standard electrode potentials (in V) in various solvents. The rubidium ion, which possesses a large radius and shows a low deformability, has a rather low and constant solvation energy in all solvents.1 As a result, the rubidium electrode is taken as a standard reference electrode in all solvents. 

Table 5 compares the standard potential of the electron electrode in hexamethylphosphotriamide (5 °C) with the standard potentials of alkali metals (25 °C). Data for liquid ammonia are also given. In both solvents the rubidium electrode potential serves as a reference point since it depends very little on the solvent. It is seen from the Table that in both solvents the standard equilibrium potential of the electron electrode is more positive than that of a lithium electrode and is close to the potentials of other alkali metals. In the course of experiment, cathodic production of dilute solutions (10 — 10 mol/1) of solvated electrons takes place and this makes the electron electrode equilibrium potential more positive compared to the standard value. In case of hexamethylphosphotriamide the same happens when electrons are bound in strong non-paramagnetic associates by the cations of all alkali metals except lithium (see Sect. 4). This enables one to assume that under the conditions of the experiments the electron-electrode equilibrium potential in liquid ammonia and hexamethylphosphotriamide is more positive than the equilibrium potential of all alkali metals. This makes thermodynamically possible primary cathodic generation of solvated electrons in solutions of all alkali metal salts in the two solvents. 

H. Strehlow in The Chemistry of Non-Aqueous Solvents, Vol. I (J. J. Lagowski, ed.). Academic Press, New York, N.Y. (1966). Chapter 4. Values from (3a) Ho, (3b) Pleskow s rubidium electrode postulate, and (3c) ferrocene and cobalticene redox couples, assumed to have potentials unaffected by solvent... 

In the many reports on photoelectron spectroscopy, studies on the interface formation between PPVs and metals, focus mainly on the two most commonly used top electrode metals in polymer light emitting device structures, namely aluminum [55-62] and calcium [62-67]. Other metals studied include chromium [55, 68], gold [69], nickel [69], sodium [70, 71], and rubidium [72], For the cases of nickel, gold, and chromium deposited on top of the polymer surfaces, interactions with the polymers are reported [55, 68]. In the case of the interface between PPV on top of metallic chromium, however, no interaction with the polymer was detected [55]. The results concerning the interaction between chromium and PPV indicates two different effects, namely the polymer-on-metal versus the metal-on-polymer interface formation. Next, the PPV interface formation with aluminum and calcium will be discussed in more detail. 

The most common selective detectors in use generally respond to the presence of a characteristic element or group in the eluted compound. This is well illustrated by the thermionic ionisation detector (TID) which is essentially a flame ionisation detector giving a selective response to phosphorus- and/or nitrogen-containing compounds. Typically the TID contains an electrically heated rubidium silicate bead situated a few millimetres above the detector jet tip and below the collector electrode. The temperature of the bead is maintained... 

Fig. 1. Simultaneous separation and detection of anions and cations on a latex agglomerate column. Column Dionex HPIC-CS5 cation exchange column (250X2 mm) with precolumn HPIC-CG5 (50 X 4 mm) eluent 0.5 mM copper sulfate, pH 5. 62 flow rate 0.5 ml/min sample volume 20 gl containing 0.1 m M of each ion detection two potentiomet-ric detectors equipped with different ion-selective electrodes in series. Peaks (1) chloroacetate, (2) chloride, (3) nitrite, (4) benzoate, (5) cyanate, (6) bromide, (7) nitrate, (8) sodium, (9) ammonium, (10) potassium, (11) rubidium, (12) cesium, (13) thallium. Reprinted with permission from [10].

Rubidium has been determined in pine needles (SRM 1575) to demonstrate the resistance to interferences of the immersed electrode with CW laser excitation38). The concentration of matrix components such as calcium and potassium were on the order of 40 pg/ml. The measured rubidium concentration of 11.1 pg/g agreed well with the certified value. 

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