Water separation index, modified

The ASTM D-3948 Water Separation Index, Modified (WSIM) Test is used to identify the emulsifying tendencies of additives in jet fuel. A high concentration of film-forming corrosion inhibitors has been shown to severely degrade the water separation tendencies of jet fuel. Treat rates as low as 20 ppm of some inhibitors can degrade the WSIM to a failing rating. 

NOTE This test is often called the Water Separation Index, Modified (WSIM) test, named after the original water separation index procedure. 

The mobile phase consists of one or more solvents that are pumped through the chromatographic system, resulting in the separation of analytes. Mobile phases may also contain modifiers. Examples of frequently used solvents include hexane, methanol, 2-propanol, acetonitrile (ACN), and water. Examples of modifiers include tri-fluoroacetic acid, acetic acid, or formic acid. In general, the composition of the mobile phase should be kept simple. Factors that influence the choice of mobile phase include the solubility of the sample in the mobile phase, the polarity of the mobile phase, ultraviolet absorption wavelength, refractive index, and viscosity of the solvents. The purity of the solvents in the mobile phase is also important because the region of UV that is used for the detection of lipids (200-215 nm) must be free of interferences. For phospholipids, the most popular solvent systems are transparent to UV in the range of 200-215 nm they include... 

Morrall2 used a HPLC system with two columns. The first column was loaded with the controlled pore glass (CPG) to be modified. The second column was used for separation of the reaction effluents. This column was coupled to a refractive index detector, allowing for quantitative detection of the effluents. The reaction was initiated by injecting an APTS/toluene mixture and stopped by injection of pure toluene. With this so-called stop-flow mechanism reaction times down to 18 seconds could be used. From these analyses it became evident that upon mixing of the aminosilane with the silica, a very rapid physisorption occurs. The initial adsorption of the APTS (from toluene solution on dried CPG) occurred before the 18 second minimum time delay of the stop-flow apparatus. For non-aminated silanes the adsorption proved to be much slower. This study also revealed the pivotal role of surface water in the modification of siliceous surfaces with alkoxysilanes, as discussed in the previous chapter. 

Fig. 11.4.5. Separation of simple saccharides. Chromatographic conditions column, LiChrosorb Si 60 (5 jam) (250x4.0 mm) mobile phase, acetonitrile-water (75 25) containing 0.01% amine modifier flow rate, 3.0 ml/min detection, refractive index. Peaks Ri, ribose X, xylose F, fructose G, glucose S, sucrose Ma, maltose L, lactose Mb, melibiose Mt, maltotriose. Reproduced from Wight and Van Niekerk (1983b), with permission.

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