Methanol phase, effect

Hexafluorophosphate retention dependencies similar to the one shown in Figure 4-56 [169] were observed on different stationary phases, but only when acetonitrile was used as an organic eluent component. If acetonitrile was substituted with methanol, the effect of the increase of PFe retention with the increase of organic concentration disappears. This indicates that liophilic ions show strong dispersive interactions with acetonitrile and have little affinity to the hydrophobic adsorbent surface—as opposed to the amphiphilic ions, which... 

Because methanol is not very polar, the elution of strong organic acids and bases requires a mobile phase with even greater polarity. This has normally been done by adding a very low concentration of acids or bases into methanol, and then the modified methanol is mixed with CO2 for separation. Citric, acetic, and chlorinated acetic acids have been used as acidic secondary modifiers, whereas isopropylamine, triethy-lamine, and tetrabutylammonium hydroxide have been served as basic secondary modifiers. A good example with ternary systems is the separation of benzy-lamines, as shown in Fig. 1. None of the three tested amines were effectively eluted by pure CO2 (Fig. la) however, some of these amines were eluted with very poor peak shapes when methanol was added to the CO2 (Fig. lb). However, the addition of isopropylamine to the methanol-modified mobile phase effectively eluted all of the three benzylamines and dramatically improved the peak shapes, as shown in Fig. Ic. 

Two layers are formed on mixing. A few crystals of CUSO4 5 H2O are now added and the mixture stirred well. The flask is closed with a stopper and left to stand for several hours. The supernatant liquid is decanted off, the solution filtered and placed in the measuring cylinder. A few mL of xylene (previously been colored with Sudan III dye) are added. This deep red liquid forms the upper phase below it is the colorless methanol phase and at the bottom the aqueous phase which is colored blue by the copper sulfate. The measuring cylinder is closed with a cork stopper and sealed with paraffin. The mixture remains stable for several years. Prior to each demonstration the liquid is shaken thoroughly the cylinder is placed in front of a white background and the red, white and blue cocktail effect presented. 

Soon after, Howard and Martin (1950) published an account of the first use of what was to become known as reversed-phase chromatography. Instead of using a polar stationary phase, such as silica or calcium carbonate, to sorb polar compounds from a nonpolar solvent, they made the stationary phase nonpolar to sorb the nonpolar compounds from a polar solvent. They treated silica with dichlorodimethylsilane, which modified the surface of the silica to a nonpolar phase. This phase effectively held a nonpolar solvent stationary while a polar solvent was acted as a mobile phase. They separated long-chain fatty acids in an aqueous-methanol (80 20) mobile phase by partitioning of the solutes into the nonpolar stationary phase, which was n-octane saturated with methanol. 

Another approach is to go directly to an eluent that is miscible with water, such as methanol. This approach is most effective when the method of detection is liquid chromatography. The methanol also effectively wets the smallest pores and removes bound water, replacing it with methanol. The methanol effectively infiltrates the C-18 bonded phase and elutes the atrazine efficiently. A third choice is a solvent, such as ethyl acetate, that effectively replaces water bound at the surface of the sorbent and infiltrates the C-18 bonded phase. However, the ethyl acetate has a low solubility for water, so that the water is displaced from the sorbent as a second phase and is pushed out ahead by the ethyl acetate during the elution process. Thus, in the example of atrazine analysis by GC/MS, either the ethyl acetate or the chloroform-methanol are two examples of eluting solvents. 

The solvent reservoir contains the mobile phase, which is typically made up of mixtures containing water and an organic modifier such as acetonitrile or methanol and/or buffer solutions. However, complex separations may require more complex mobile phase compositions. The mobile phase assists in the transportation of compounds in a mixture through the stationary phase, effecting separation into the individual components. This will be further discussed in Chapters 3 and 4. 

Energy (au) in gas phase Energy (au) in methanol Solvent effect (kcal/mol)... 

Catalytic gas-phase reactions play an important role in many bulk chemical processes, such as in the production of methanol, ammonia, sulfuric acid, and nitric acid. In most processes, the effective area of the catalyst is critically important. Since these reactions take place at surfaces through processes of adsorption and desorption, any alteration of surface area naturally causes a change in the rate of reaction. Industrial catalysts are usually supported on porous materials, since this results in a much larger active area per unit of reactor volume. 

The concentrations of benzoic acid, aspartame, caffeine, and saccharin in a variety of beverages are determined in this experiment. A Gig column and a mobile phase of 80% v/v acetic acid (pH = 4.2) and 20% v/v methanol are used to effect the separation. A UV detector set to 254 nm is used to measure the eluent s absorbance. The ability to adjust retention times by changing the mobile phase s pH is also explored. 

Reversed-phase hplc has been used to separate PPG into its components using evaporative light scattering and uv detection of their 3,5-dinitroben2oyl derivatives. Acetonitrile—water or methanol—water mixtures effected the separation (175). Polymer glycols in PUR elastomers have been identified (176) by pyrolysis-gc. The pyrolysis was carried out at 600°C and produced a small amount of ethane, CO2, propane, and mostiy propylene, CO, and CH4. The species responsible for a musty odor present in some PUR foam was separated and identified by gc (Supelco SP-2100 capillary column)... 

Early [1, 2] it was reported about RP-HPLC the separation of amino derivatives of 3-chloro-l,4-naphtoquinone with methanol mobile phase. In some cases changing organic modificator in eluent leads to the progress in effectiveness of sepai ation. In present work the compaiison was performed for separation of some amino derivatives of 3-chloro-I,4-naphtoquinone by RP-HPLC with methanol and acetonitrile eluent. It has been shown that certain differences exist for vaiious derivatives mentioned above. 

Methanol is frequently used to inhibit hydrate formation in natural gas so we have included information on the effects of methanol on liquid phase equilibria. Shariat, Moshfeghian, and Erbar have used a relatively new equation of state and extensive caleulations to produce interesting results on the effeet of methanol. Their starting assumptions are the gas composition in Table 2, the pipeline pressure/temperature profile in Table 3 and methanol concentrations sufficient to produce a 24°F hydrate-formation-temperature depression. Resulting phase concentrations are shown in Tables 4, 5, and 6. Methanol effects on CO2 and hydrocarbon solubility in liquid water are shown in Figures 3 and 4. 

Methanol eoncentration has essentially no effect on predicted water content of the liquid-hydrocarbon phase. The water eontent (not shown in the tables) was about 0.02 mol%. 

Figure 3. Effects of methanol on predicted CO2 solubility in water phase.

For this problem, methanol had no practical effect on the solubility of hydrocarbons in the water phase (Figure 4). 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

Silica gel, per se, is not so frequently used in LC as the reversed phases or the bonded phases, because silica separates substances largely by polar interactions with the silanol groups on the silica surface. In contrast, the reversed and bonded phases separate material largely by interactions with the dispersive components of the solute. As the dispersive character of substances, in general, vary more subtly than does their polar character, the reversed and bonded phases are usually preferred. In addition, silica has a significant solubility in many solvents, particularly aqueous solvents and, thus, silica columns can be less stable than those packed with bonded phases. The analytical procedure can be a little more complex and costly with silica gel columns as, in general, a wider variety of more expensive solvents are required. Reversed and bonded phases utilize blended solvents such as hexane/ethanol, methanol/water or acetonitrile/water mixtures as the mobile phase and, consequently, are considerably more economical. Nevertheless, silica gel has certain areas of application for which it is particularly useful and is very effective for separating polarizable substances such as the polynuclear aromatic hydrocarbons and substances... 

As a final example of column durability and solvent resistance in small pore gels we were able to resolve nylon 6 oligomers using a methanol mobile phase and 205-nm UV detection as shown in Figure 13.29. In fact, polar solvents such as acetone, acetonitrile, methanol, and 2-propanol, are used routinely as needed with no ill effects. 

The purpose of this study is twofold to compare four linear aqueous SEC columns made by Tosoh and Showa Denko in terms of composition and performance and to evaluate the effect of commercial PEO standards on the accuracy and precision of the MW and MWD of polyvinylpyrrolidone (PVP) and NIST PEO standards. In terms of performance, emphasis will be placed on factors not commonly covered by column manufacturers. Successful SEC conditions for PVP in water, in water/methanol, and in dimethylformamide can be found in the literature (8,9,10). This study deals mainly with the effects of column, mobile phase, and PEO standards on the MW and MWD of PVP. 

Commercial grades of PVP, K-15, K-30, K-90, and K-120 and the quaternized copolymer of vinylpyrrolidone and dimthylaminoethylmethacrylate (poly-VP/ DMAEMA) made by International Specialty Products (ISP) were used in this study. PEO standard calibration kits were purchased from Polymer Laboratories Ltd. (PL), American Polymer Standards Corporation (APSC), Polymer Standards Service (PSS), and Tosoh Corporation (TSK). In addition, two narrow NIST standards, 1923 and 1924, were used to evaluate commercial PEO standards. Deionized, filtered water, and high-performance liquid chromatography grade methanol purchased from Aldrich or Fischer Scientific were used in this study. Lithium nitrate (LiN03) from Aldrich was the salt added to the mobile phases to control for polyelectrolyte effects. 

In summary, methanol as a mobile-phase modifier has a significant effect on the separation of PVP in aqueous SEC with these four linear columns. The best separation of all PVP grades can be achieved with the SB-806M column in 50 50 water/methanol with 0.1 M lithium nitrate. It is interesting to note that despite the improvements reported by the manufacturers for the newer columns (SB-806MHQ and PWxl), the newer columns do not necessarily perform better than the older columns (SB-806 and PW) for aqueous SEC of PVP. 

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