Solvents Instability, Reactivity, and Denaturants

If the exact solution composition is critical, then the sparge gas may be presaturated by placing the sparge line in a solvent reservoir filled with mobile phase. The effluent gas from this bottle is then used to sparge the actual in-use solvent. The sparge solvent should be replaced ftequently. 

The problem of preferential volatilization alw s increases as the volume of the solvent in the solvent reservoir decreases. To virtually eliminate the problem of changing solvent composition, a blanket sparge with frequent replacement of solvent with fresh is recommended. 

In normal HPLC work, temperatures of 60°C and above are considered high. To skirt the reservoir temperature issues, lengths of column tubing are sometimes placed in heaters and used to raise the solvent temperature. It should be noted that water at elevated temperatures is very aggressive and can cause rapid and irreproducible damage to silica-based columns and other HPLC components. Therefore, regardless of what technique is used, review of the pun, injector, and detector operation manuals is critical to make sure that each and every instrument component is compatible with high-temperature use. 

Some classes of solvents are inherently unstable. Final breakdown products and/or intermediates may themselves be chemically reactive or alter the chromatographic properties of the solvent enough to be a cause of concern to the analyst. To further illustrate this, two classes of solvents (ethers and chlorinated solvents) and acetone will be discussed. Ethanol, due to its highly regulated status in its neat (or 200 proof) form, is often available in a denatured ft rm. There are many denaturants for ethanol and they will be presented in this section. Finally, problems associated with water will be considered with regard to the pluses and minuses of manufactured versus inhouse-produced sourcing. 

If questions aiise with regard to the stability of any given solvent, refer to any of a number of safety manuals [26,27] or call the solvent manufacturer directly. 

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