溶剂稳定性

Like other chemicals, solvents will degrade over time. Solvent deterioration is dependent on several factors - elapsed time since purification, shipping and storage conditions, individual solvent properties and the presence or absence of stabilizers. Most Honeywell Burdick & Jackson solvents are inherently stable and relatively inert. However, several solvents require chemical stabilizers to prevent or slow degradation. Certain less stable solvents are also available without additives because no suitable preservative exists that will not interfere with a specific analytical method. All these solvents require special handling to minimize degradation problems. Elevated levels of some solvent degradation products may even present safety hazards.

Handling Less Stable Solvents
It is best to avoid less stable solvents when developing methods. Unfortunately, some procedures require their use. Most solvent manufacturers recommend using a product within one year. This timetable begins on the date of solvent manufacture and not when the consumer purchases or receives it.

All solvents should be stored in a controlled environment. Keep unopened containers in a vented, approved flammable liquid storage cabinet at room temperature and minimize exposure to light, heat and oxygen. Repeated or rapid temperature variations may lead to package breathing or leakage. This breathing exposes the solvent to air which can accelerate degradation as well as contaminate the solvent. Once opened, an unstabilized solvent should be blanketed with clean argon or nitrogen and tightly recapped. These solvents should be monitored regularly for evidence of degradation.

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.

Ethers
Light, heat or oxygen cause ethers to form free radicals that generate peroxides. Peroxide formation raises several concerns. Their explosive nature makes safety the most serious issue when handling peroxide-containing solvent. Also, peroxides in any solution can react with analytes or degrade column packing materials when used in liquid chromatography mobile phases. To minimize peroxide-related problems, purchase ethers in quantities small enough to ensure their use within 30 days after opening. As an added safety precaution, test the solvent for peroxides prior to use.

Ether Testing
Many peroxide testing procedures are available, but simply shaking a 1:1 (v/v) mixture of an ether sample with 10% aqueous potassium iodide solution will detect peroxides. A colorless or faint yellow solution indicates low-level peroxide contamination, but a dark yellow or brown color indicates significant peroxide levels. Solvent manufacturers employ several procedures to minimize ether degradation. One method is to eliminate one or more of the sources leading to free radical formation. Manufacturers blanket the solvent with inert gas during bottling to remove oxygen and use amber bottles to shield the solvent from UV light. These packaging techniques protect the solvent until the bottle is opened. Another method to extend solvent shelf life involves adding stabilizers.