Solid-state reference

In the preparation of many solid state reference materials, reduction of the grain size plays an important role. Usually this reduction is required because of the measurement methods to be used both in the projects and later by the users of the reference material, as well as to come to an acceptable minimum sample intake. The minimum sample intake can be defined as the minimum amount of material needed, so that the heterogeneity of the material does not affect the repeatability of the measurement method. The reduction of the grain size is usually implemented by crushing and/or grinding techniques. The techniques employed and the equipment used must be suitable for the purpose of processing the material. Potential problems of contamination, loss of volatile components, and/or other physical and... 

The solid state reference electrode has no internal Cl solution but uses Cl ions in the mobile phase to keep its potential constant. This means that a certain amount (typically 1 to 10 mM) KC1 must be dissolved in the mobile phase. 

The intermediate formation of alkyl peroxide complexes has been postulated, and in several cases observed with spectroscopic and spectrometric techniques in several selective procedures based on metal catalyzed oxidation with hydroperoxides, Ti and V ions being among the transition metals most widely used for this purpose. However, to date the few examples of alkyl peroxide complexes isolated and characterized in the solid state refer to (dipic)V0(00Bu-f)(H20) 8, synthesized by Mimoun and coworkers in 1983, and to a dimeric Ti complex [((/7 -OOBu-f)titanatrane)2(CH2Cl2)3] 9, synthesized by Boche and coworkers. ... 

Another opportunity to realize constant activity of the potential determining ion at the reference interface appears when one chooses the solid electrolyte in such a way that the ion of the redox couple is the same as one ion of the major component of the electrolyte. In that case, the change of the activity due to the electrode reaction with the gas can be neglected against the overall constant activity of that ion in the salt. This is the solid-state reference arrangement. An example is the chlorine sensor (Fig. 6.40), in which the reference potential is set up by the constant activity of CP in the solid AgCl electrolyte. This arrangement is equivalent to a reference electrode of the second kind, discussed in Section 6.2.2.1. 

In order to fully utilize solid-state ion sensors in potentiometric measurements there is a need for a durable and reliable solid-state reference electrode as well. It was shown recently that it is possible to construct... 

Jayaweera P, et al. Solid state reference electrode for high temperature electrochemical measurements. U.S. Patent 5,425,871, June 1995. 

The compounds in this report usually contain a chirotopic stereogenic carbon ring atom, and were prepared as racemic mixtures. Hypothetically, if the BC conformation prevails, then one can imagine two enantiomers in solution (reference, 5)-BC 9 and (retro-inverso,R)-BC 9-bar. Since this stereochemistry is complicated, it will be helpful if we refer to the descriptor for only one enantiomer. Therefore, in an arbitrary but consistent manner in this report, we will always define the reference ring chirality and label tropicity to be that of the (S)-enantiomer. For example, suppose a racemic mixture of (reference,S)-BC 9 and (retro-inverso,R)-BC 9-bar affords crystals belonging to an achiral space group so that both enantiomers in the racemic compound are present in the crystal lattice. Let us further suppose that dissolution of these crystals will give the same solution-state conformation. We will write that the solid-state (reference,S)-BC 9... 

The racemic mixture of (1 / .S 3.S / )-3-methyl-1-phenyl-1,3,4,5,6,7-hcxahydro-2, 6-benzoxazonine-6-carbonitrile (43) crystallized as a racemic compound in an achiral space group crystal.3 CA-to-phenyl substitution of a methyl at C(3) did not change the solid-state (reference,S)-SCBtype2 conformation of the parent nine-membered... 

Nolan, M.A., Tan, S.H., Kounaves, S.P. (1997). Fabrication and characterization of a solid state reference electrode for electroanalysis of natural waters with ultramicroelectrodes. Anal. Chem. 69 1244-7. 

Solid-state—Refers to the exploitation of the electric, magnetic, or light-producing capabilities of solids without depending on electron tubes. 

There are no solid-state reference compounds with U in a formal -t3 or +2 oxidation state. 

Solid-state reference electrodes for potentiometric sensors are currently under research. The main problem to be faced in developing this type of electrode lies in connecting the ionic conducting (usually aqueous) solution with an electronic conductor. Since the reference electrode has to maintain a defined potential, the electrochemical reaction with components of the electrolyte has to be avoided. Oxides, mixed oxides, and polyoxometalate salts of transition elements can be proposed for preparing solid-state reference electrodes. Tested compounds include tungsten and molybdenum oxides (Guth et al., 2009). 

Guth, U., Gerlach, E, Decker, M., Oelssner, W, and Vonau, W. 2009. Solid-state reference electrodes for potentiometric sensors. Journal of Solid State Electrochemistry 13, 27-39. 

Figure 13.9 Schematic of reference electrode, (a) Gas-phase reference (b) Solid-state reference (c) Reference with electrolyte chain.

Schwandt, C. and Fray, D.J. (2006) The titanium/hydrogen system as the solid-state reference in high-temperature proton conductor-based hydrogen sensors./. Appl. Electrochem., 36, 557-65. 

The temperature function is of the type given in Section 25.2.6. It can be experimentally determined using solid-electrolyte cells with solid-state reference electrodes [22]. 

Also for sensors with sulfate electrolytes in the region of application above 8(X)°C no stable Ag/Ag reference electrodes could be found (37). Better results were achieved with the solid state reference systems Mg0,MgS04 and Mn0,MnS04 Again, in the case of sulfate solid electrolyte sensors the most stable and lelieable reference electrodes were those with flowing reference gas. 

In recent years, the so-called solid-state reference electrodes have been developed for application in solution electrochemistry. In these electrodes, an electron conducting element (e.g. a silver wire or a silver layer) is first covered with a solid salt layer (e.g. silver chloride) and then with a second solid salt/polymer layer (e.g. a mixture of silver chloride and potassium chloride in PVC) Finally, the electrode is covered with a polymer, for instance cellulose acetate is deposited (cf. Fig. III.2.5) [21]. The influence of the polymer on the properties of such electrode was investigated by Lee et al. [22]. Because these electrodes can be fabricated in a very small size and because only small amounts of the electrolyte are dissolved, these electrode systems are often used in microelectrode arrangements for medicinal measurements. 

Although all solid state reference electrodes based on conducting polymers have been tested, they are still in the testing phase. The most promising systems appear to be bilayers with different ion-exchanger properties such as glassy carbon/polypyrrole in conjunction with a polypyrrole(polystyrene sulfonate) layer 64,65). 

Vonau W, OelBner W, Guth U, Henze J (2010) An all-solid-state reference electrode. Sens Actuators B 144 368-373... 

Regarding the reference electrode, the conventional Ag/AgCl/KCl electrode is often adapted to the presence of organic solvents and the different conductivity and ionic mobility in the typical HPLC mobile phases by using a porous ceramic frit for the electric contact or by replacing the KCl internal solution by a low-maintenance gel. Solid-state reference electrodes made of Ag or Pd has also been included in commercial equipment. Finally, auxiliary electrodes are currently made of metal and they are often little more than the stainless steel outlet from the cell. 

Add distilled water to solid sample Use flat bulb combination electrode Use pressurized or solid state reference electrode Sterilize electrodes... 

Under conditions of high pressure, the positive flow of filling solution from the reference junction must be maintained. Otherwise the sample is forced up the junction and contaminates the internal. Two common methods of ensuring positive flow are the use of a reference with a side arm or the use of a solid state reference. The reference with a side arm can be pressurized with slightly greater pressure than the sample. Some solid state reference electrodes are constructed with a pressurized internal which prevents diffusion of the sample into the electrode body. 

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