Smaller bottles will be used more quickly, thereby minimizing the potential for peroxide problems and solvent waste. Chlorinated Solvents Chlorinated solvents such as chloroform and dichloromethane degrade at varying rates. Susceptibility to degradation depends on the solvent type and storage conditions. Light, heat or oxygen can initiate free radical formation resulting in phosgene, hydrochloric acid and other degradation products. To improve solvent stability and increase shelf life, solvent manufacturers add preservatives to chlorinated solvents.
Pure chloroform is unstable and rapidly generates free radical degradation products.
Although many additives can inhibit this decomposition process, alcohols and olefins are the most successful and widely used preservatives. Olefins act as free radical scavengers and remove decomposition products such as hydrochloric acid. Although amylene is the most common additive, chloroform is also available with amylene and ethanol. Because ethanol will increase mobile phase polarity and therefore affect the analysis, methods that use chloroform should state whether or not ethanol is included as a preservative. Chloroform Testing Verify chloroform integrity prior to use by testing an aqueous extract for free chloride using an AgNO 3 solution.