Organic modifier effect acetonitrile solvent

Some advice can be formulated for the choice of organic modifier, (i) Acetonitrile as an aprotic solvent cannot interact with residual silanols, whereas the protic methanol can. Thus, when measuring retention factors, methanol is the cosolvent of choice, as it reduces the secondary interactions between the solutes and the free silanol groups, (ii) For the study of the performance of new stationary phases one should use acetonitrile, as the effects of free silanol groups are fuUy expressed [35]. (iri) Acetonitrile with its better elution capacity can be considered as the best organic modifier for Hpophilicity measurements of highly Hpophihc compounds with adequate stationary phases [36]. 

Wennrich [167] optimised important accelerated solvent extraction parameters, such as extraction temperature and time, using a spiked wetland soil. The effect of small amounts of organic modifiers on the extraction yields was studied. An extraction temperature of 125 °C and ten-minute extractions performed three times proved optimal. Two accelerated solvent extraction-solid-phase microextraction procedures without and with an organic modifier (5% acetonitrile) were evaluated with respect to precision and detection limits. 

C. Effect of Organic Solvent The addition of organic solvents to buffers alters the viscosity of the buffer and may also affect the intramolecular hydrogen bonding. Therefore, organic modifiers such as acetonitrile and methanol are often added to buffers to improve resolution. 

Variations in the selectivity are sometimes observed with the change in the type of organic modifier due to the specifics of the analyte-solvent interactions (solvation) and the specific adsorption behavior of the organic modifier. In the following example the effect of type and concentration of methanol and acetonitrile modifiers on the retention of acidic, basic, and neutral analytes is discussed. 

The organic solvents often used as modifiers in the aqueous mobile phase consist of n-propanol, isopropanol, methanol, and acetonitrile. They are efficient agents for modulating the hydrophobic interaction between the analytes and the protein stationary phase [144]. An increase in the organic modifier in the aqueous organic mobile phase will decrease the retention, but will have minimal effect on the overall enantioselectivity [141]. 

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. 

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