SPE Technology

Supporting electrolyte-free electrolysis is an ideal way to realize perfed green synthesis assisted by electricity. Solid polymer electrolyte (SPE) technology, devel- 

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Innovative SPE technology employing microelution plate design is shown in Fig. 2.4. Tip design of the well plate provides a smaller surface... 

Early examples of the industrial application of this process (e.g. in the 1970s, General Electric [2] used first-generation ion-exchange membranes and SPE technologies) were not successful, mainly because of stability and activity/performance problems with the GDE. 

Recently, three papers have reported the determination of risperidone and its active metabolite 9-hydroxyrisperidone using LLE and SPE technologies. The analytical columns used to separate these compounds were C4 or C18 bonded phases of 3 pm or 5 pm particle sizes with UV/VIS detection. Mobile phases consisted of phosphate bufiers (pH 3-4) in acetonitrile. The sample volumes used ranged from 200 pi to 1 ml, with extraction recoveries averaging 90%. The limits of quantitation ranged from 0.5 to 10 ng/ml in human plasma (Nagasaki et al., 1999 Avenso et al., 2000 Titier et al., 2002). A study by Titier showed the simultaneous determination of clozapine, olanzapine, haloperidol, risperidone, and its active metabolites by RP-HPLC in human plasma. The assay involved LLE with a hexane/isoamyl alcohol mixture... 

Several other methods have been published using RP-HPLC for the determination amphetamines and related derivatives. Studies have shown the determination of amphetamine and related derivatives in plasma, urine, and hair by RP-HPLC with precolumn derivatization and either UV/VlS or fluorescence detection. Various methods are employed by SPE technologies using Cl8 cartridges for sample cleanup prior to derivatization. The derivatized compounds were separated on analytical columns of various Cl 8 bonded phase materials. The methods generally used water/acetonitrile mobile phases operated in gradient mode. All studies reported extraction recoveries of 85-102% for all the analytes, with LLOQs ranging from 5 to 60 ng/ml (Tedeschi et al., 1993 Ealco et al., 1996 Hernandez et al., 1997 Al-Dirbashi et al., 1997 Al-Dirbashi et al., 2000 Soares et al., 2001). 

More importantly, in the SPE technology gaseous H2 and O2 are liberated on the electrode surface on the side of the solution, thus solving the problem of the solution resistance due to the presence of bubbles. The membrane acts as an electrolyte. At the anode H2O is oxidized to O2 with liberation of H, which migrates through the membrane to the cathode, where it is reduced to H2. In practice, a flow of solution is needed only at the anode to replace water molecules oxidized to O2. However, the solution no longer needs to be conductive since no current passes through it. Actually, SPE electrolyzers are fed with plain water [20]. 

The SPE technology solves some problems but it poses others. In particular, the strong acid environment developed on the membrane calls for a complete change of electrode materials from those used in the conventional alkaline electrolysis. More specifically, especially the requirements for electrode materials for O2 evolution are stringent since the anodic conditions are especially aggressive for corrosion problems. 

M. Henry, SPE technology principles and practical consequences, in N. J. K. Simpson, ed., Solid-Phase Extraction Principles, Techniques, and Applications, Marcel Dekker, New York, 2000, pp. 125-182. 

The advantages of SPE technology are as follows electro-organic synthesis without an additional supporting electrolyte, reduced energy demand for separation and recycling processes, and elimination of side reactions with the electrolyte at moderate reaction conditions with ease of process control. 

Often the starting point in these analyses is how to automate existing processes. This may not be practical and may involve a great deal of time and resources, ft is often better to rethink a traditional process from an automation point of view. A classic example of this is the effort that many companies have invested in the automation of a traditional aqueous workup. Mixing of biphasic mixtures has led to many problems. A better solution, in this case developed by rethinking the problem, is to use solid phase extraction (SPE) technology. 

Compared to alkaline electrolysis, material costs are high for SPE electrolysers. The advantage of the SPE technology lies in a higher gas quality - especially in part load operation. Using a solid electrolyte also makes higher pressure possible as the absence of alkaline solution provides better sealing options. Some suppliers of SPE electrolysers are listed in Table 5.2. 

In all cases, SPE technology involves Nafion membranes and there exist two different ways for obtaining a structurally stable, membrane-electrode assembly. 

The first applications of Nafion membranes in SPE technology were in fuel cells for space applications, which have been developed since the end of the 1960s. The perfluorosulphonic polymer is used as a proton conductor which provides to the cathode the protons that have been generated electrochemically at the anode. Perfluorosulphonic SPE is particularly well-suited to this application ". The principle of the H2"C>2 fuel cell is shown schematically in Fig. 32.3. At the anode, gaseous hydrogen is reduced following the electrochemical reaction... 

Storage cell-batteries based on SPE technology have been recently developed In the electrochemically generative hydrogen bromide cell, the overall reaction is the following... 

SPE technology, despite the fact that the conductivity of pure water is low, the working potential difference is minimal due to the low electrical resistance of the proton conducting membrane separating the electrodes. 

These techniques are not necessarily used alone. Some recent reports combine PEE with solid-phase extraction (SPE) technologies that include the use of... 

R.S. Yeo, Intrinsic Conductivity of Perfluorosulfonic Acid Membranes and its Implication to the Solid Polymer Electiolyte (SPE) Technology, In R.S. Yeo, T. Katan, and D.T. Chin (eds). Transport Ptvcesses in Electrochemical Systems, Electrochemical Society, Pennington, NJ (1982), p. 178. 

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