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 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.
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.
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