Dual-phase water system

A large problem in polymer electrolyte membrane fuel cell operation is a possible partial condensation of water vapor when temperature gradients are present in the fuel cell and a dual-phase water system develops. 

The difficulties and low-throughput nature of the experimental dual determination, especially in alkane-water systems, the development of other techniques more amenable to automation, as well as more refined computational approaches for octanol-water systems, aU have contributed to Umit the use of the alkane-water system as a second bulk-phase system. However, efforts have been devoted to the development of log (alkane) computational prediction methods by Rekker et al. [13] as well as Caron and Ermondi [14]. 

A knowledge of the extraction equilibria between the organic and aqueous phases helps to identify the operational variables that can control the solvent extraction process. An example - the extraction of copper from a copper sulfate solution using a chelating reagent (HR) - is considered. This is one of the best studied examples of solvent extraction. Normally, the system would not be described as a water-hydrocarbon dual-phase system, as it is in fact the Cu2+, SO-, H+, R-, and R-, and the equation... 

The pump consists of dual reciprocating pistons which are hydraulically controlled. Oil is distributed by the system to the two pistons which are 180° out of phase (as with the Altex and Waters systems). A fixed volume of hydraulic fluid is delivered to the control system for every revolution of a special gear pump. The latter is controlled by a motor having a constant speed and a tachometer feedback circuit. Other compensating circuits... 

HPLC was performed using Waters 600S solvent delivery system (Waters, Milford, MA, U.S.A.). 2487 UV dual channel detector of Waters was used and injector (20 fit sample loop) from Rheodyne. The data acquisition system was Millenium (Waters). Water filtered 1 Milipore ultra-pure water system (Milipore, Bedford, MA, USA). The wavelength was fixed at 254 nm and the experiment was performed at room temperature. The size of the analytical colunm packed by C g was lS0X4.6mm (Spm) (Alltech, USA). The mobile phase of 0.75% TFA in water and acetonitrile were used in this experiment. The flow rates of the mobile phase were fixed at I ml/min. The constant volume of 0(d, was injected. This experiment was implemented at room temperature. The gradient mode was employed to isolate peptides. The complete gradient condition was listed in Table I. 

The selectivity of TLC systems was compared by use of correlations between Rf(ll) and Rf(l) (by analogy with two-dimensional TLC). The greatest spread of points, indicative of individual selectivity, was obtained for nonaqueous mobile phases on silica and aqueous mobile phases on octadecyl silica adsorbent wettable with water (RP-18 W). The correlation of Rf values in normal- and reversed-phase systems was utilized in the practical separation of a mixture of 14 triazines and urea herbicides using 2-D TLC on a Multi-K CSS dual phase (3 cm strip of octadecyl silica parallel to silica layer). The plate was videoscanned showing the real picture of the plate <2002JCH277>. 

Figure 11.36 Schematic diagram of the dual-column extraction system on-line via a Valeo 10-port switching valve with the chiral LC-MS/MS system. The components were as follows PI, a Leap Technologies autosampler with two HPLC pumps delivering mobile phases A and B to the extraction column EC-1 or EC-2 (Waters Oasis HLB 25 gm, 1 x 50 mm) P2, HPLC pump system delivering isocratic elution mobile phase through the extraction column to the chiral analytical column full bold arrows, pathway for mobile phase A (Table) used to load plasma sample onto extraction column dashed arrows, pathway for mobile phase (neither A nor B) used to elute analytes from extraction column to the chiral analytical column F, in-line filter G in-line guard column MS, a triple-quadrupole instrument in MRM mode. Reproduced from Xia, J. Chromatogr. B 788, 317, copyright (2003) with permission from Elsevier.

Fig. 7.2 HPLC separation of hyoscyamine 1 and scopolamine 6. The analysis was performed by using Waters HPLC system, equipped with Waters 1,525 binary pump, a Dual X Waters 2,487 absorbance detector, and Symmetry C18 reversed phase chromatographic column (250 mm x 4.6 mm, 5 pm). The operation temperature was 26 °C. The mobile phase consisted of acetonitrile methanol 0.05 mol ammonium acetate (20.9 27.9 51.2), and elution speed was 0.6 mL min in isocratic regime...

Upon increasing the temperature of calcination, the phase changed from a dual phase system of A1(P03)3 and SiP207. to a single phase of AlSi2P30i2. This modification of phase improved the affinity to water and the surface stability, which enhanced the stability in water and the capillary force. The ceramic fiber based coupon showed a 5 times higher rate of water absorption than the polymer based one. 

Pure ILs have a dual nature since they are actually molten salts or a mixture of cations and anions. They were found to have a relatively high solvent polarity, comparable to that of short-chain alcohols [4-5]. Since CCC needs to work with a Diphasic liquid system, water-insoluble ILs should be selected if an aqueous phase is desired, l-butyl-3-methylimidazolium hexa-fluorophosphate ([C4CiIm][PFg]) has limited water solubility (18 g/L or 1.3% or 63 mM [5]) and is easy to synthesize. It was the first IL used in CCC [6]. 

Humidity has a significant influence on the photocatalytic oxidation of aromatic contaminants in the gas phase. This is of particular interest, because commercial photocatalytic systems will be required to operate under a broad range of relative-humidity levels. The specific influence of relative humidity on the photocatalytic reaction has generally proved rather difficult to quantify because water has a dual role It may compete with contaminants for surface adsorption sites (a negative influence) and it plays a role in the regeneration of surface hydroxyl groups during photocatalysis (a positive influence). 

The Altex liquid chromatograph (Fig.3.29) utilizes a dual piston approach similar to that in the Waters ALC 200 instrument. The pistons are 180° out of phase. The special cam shape results in a steady flow which is interrupted by minor fluctuations. These are damped by a flow-feedback system which is incorporated into the pump. This system has been rated at a pressure of 7000 p.s.i. 

Pederson described a specific HPLC method for the determination of dipyridamole in serum [74]. The HPLC system used was a Waters model 600 liquid chromatograph equipped with a U6K injector, a pBondapak Ci8 column (30 cm x 39 mm) (10 pm), and a model 440 dual channel filter absorbance detector in conjunction with a Tarkan W + W 600 recorder. The mobile phase was a 75 25 mixture of methanol and a 0.02 M solution of sodium acetate (adjusted to pH 4 with acetic acid). The solvent flow rate of 2 mL/min was produced by an applied pressure of approximately 2000 p.s.i. Detection of the analyte was made at the UV absorption maximum of 280 nm. 

The analyses of aromatic components were performed on a 1525 Binary Waters HPLC with a dual absorbance detector using a Symmetry Cl 8 column and a mobile phase of methanol and water. Carboxylic acids analyses were performed using the same HPLC system with an Atlantis dC18 column and mobile phase. pH was monitored with a Coming 430 pH meter. For most experiments, the total organic carbon was also analyzed using a Shimadzu 5050 TOC analyzer equipped with a NDIR detector coupled with an autosampler ASI 5000. 

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