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The Proper Storage and Handling of Volatile Analytical Standards

By: Pat Myers, Reporter EU Vol 29

Properly storing and handling standards is critical to achieving accurate and reproducible analytical results. This is especially true when the analytical standard contains very volatile or gaseous components. All standards supplied by Supelco are packaged in containers that are suitable, if unopened, for long-term storage, as indicated on the label. However, once opened, standards must be transferred to new containers. We recommend using either micro reaction vessels with Mininert® valves or Certan® bottles to maximize shelf life and minimize possible component loss. Choose amber glass vessels if any components are light sensitive or clear glass vessels for better visibility. The size of the container should be matched to the volume of the standard to minimize evaporation of volatile components into the headspace. Both recommended options provide 2 lines of defense against sample loss: 1) mininert valves have a PTFE valve backed up by a cylindrical red rubber septum and 2) certain vials have a capillary tube opening backed up by a PTFE-lined cap.

Handling procedures can have a large impact on standard integrity. A big factor affecting analyte loss from volatile standards is evaporation into the headspace of the container. The only parameter infl uencing evaporation that can be manipulated by the analyst is temperature. It is important to keep volatile standards at the recommended storage temperature until the container is opened for transferring the contents to a new container or removing an aliquot for dilution. Volatile standards should not be allowed to warm to room temperature before opening. Warming will lead to evaporative loss of volatile and gaseous components into the headspace of the container and out of the container once it is opened. Additionally, it is recommended that new vials for storing volatile standards be cooled before the transfer. This can be done by fi lling the vial with dry nitrogen and chilling it in a refrigerator. Take care to wipe any external condensation from the vial before opening.

Finally, while it is generally a good practice to thoroughly mix standards before use, mixing may lead to a loss of gases and volatile components from a standard because agitation increases the surface area of the liquid, increasing evaporation rate. Therefore, shaking volatile standards should be avoided immediately before opening.

Sigma-Aldrich is a trusted source for a broad range of analytical and reference standards.

Our standards include neats, single components and multi-component calibration mixtures. All raw materials used in the production of these products have been tested for purity. Documentation is shipped with most standard purchases. Please visit our website for a complete listing of all available analytical standards.

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