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Study Notes: Shelf Life of Laboratory Solutions

Most laboratory reagents have a limited shelf life. In general, solutions should not be kept for more than one year. In a great many cases, solutions will deteriorate in less than a year.

Some solutions are chemically unstable. Over time the concentration of such solutions will change as the unstable reagents break down, or react, to form other chemicals. Sodium hydroxide solutions have a limited shelf life, because sodium hydroxide reacts with atmospheric carbon dioxide to form carbonates. Therefore, the concentration of a sodium hydroxide solution cannot be known with certainty, unless it has been freshly standardised.

There may be some evaporation of solutions kept in bottles. The moisture that condenses in the upper portion of the bottle will dilute the dispensed solution as it is poured out. In all cases, solutions should be mixed thoroughly before use.

Solutions should be routinely checked prior to use for signs of turbidity or deposits that may indicate microbial contamination or chemical degradation. Crystals around the neck of a storage bottle may indicate a change in concentration. When this occurs decisions need to be made to discard, treat or re-check the solutions.

Image of an open stock bottle Solutions must not be left uncovered for any longer than necessary, and should be returned to storage, with the lid firmly secured, as soon as the required volume of solution has been measured out. Solutions without a lid could be contaminated by external contaminants, or some of the water in the bottle could evaporate, thereby changing the concentration of the solution.

Guidelines for storing laboratory solutions
Improper storage of laboratory solutions can reduce their shelf life. The following principles should be followed when storing laboratory solutions.

  • Solutions should be kept in a cool place, preferably in the dark and certainly out of direct sunlight.
  • Solutions should be returned to storage, with the lid firmly secured, as soon as the required volume of solution has been measured out.
  • Solutions should be regularly checked, and any that have been kept beyond their shelf life; have deteriorated; have questionable labels; are leaking; have corroded caps; have precipitated out or have developed any other problem, need to be properly disposed of.
  • Solutions should be kept well sealed to avoid vaporisation and spills.
  • Solutions should be stored away from heat sources such as heaters and hot water pipes, and sources of ignition such as flames.
  • Handling full bottles of solution can be difficult when reaching overhead. Therefore, to reduce the risk that the bottles are dropped, solutions should preferably not be stored on shelves above eye level.
  • Solutions should not be stored in aisles, stairways, hallways, or on floors, desks or bench tops.
  • Solutions should preferably be stored on sturdy shelving, which has a raised lip edging and has been secured to the wall or ceiling, or in a suitable alternative that provides secondary containment, in case the containers spill or leak.
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