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Chemical Reference Standards: Don’t Just Snap and Pour (Part 2)

14 Jan 2021

Several year ago, my colleague, Alan Sensue wrote Chemical Reference Standards; don’t just snap and pour. In it, he described a personal experience where he mixed several expensive reference standards together assuming the vials contained exactly 1 mL. It was a mistake he has remembered for some time. Here are a few other examples as to why you don’t want to just snap and pour your reference standards:

Before opening the vial, it is a good practice to examine it and its contents. During shipment, vials can get bounced around on the delivery truck. As a result, a portion of the solvent can adhere in the top half of the vial. By lightly tapping the bottom of the vial on a lab bench, or lightly flicking the top of the vial with a finger, the solvent should flow to the lower portion. The below photo demonstrates what could happen. The standard was easily aliquoted into secondary container, but appears to have less than 1 mL provided. If you look closely at the snapped off top, half the solution has remained there. Don’t just snap and pour.

reference standard stuck in top of opened ampul

Some compounds, such as PAHs, cannabinoids, and PCBs may fall out of solution when stored refrigerated or frozen. For stability purposes this is the recommended storage. Prior to using these solutions in the lab, the vial contents should be examined. If you see something similar to the vial below, sonication and/or heat may be required. Once the standard is at room temperature, place the solution in a sonicator for 10-15 minutes. Additionally, a little heat (around 40°C) can help dissolve these compounds back into solution. By doing so, you will not be “missing” these compounds from your assay. This was mentioned in another blog entitled "Handling Your Analytical Reference Standards". Additionally, this post emphasized to follow the instruction on the standard’s Certificate of Analysis (CoA). Don’t just snap and pour.

precipitates in a reference standard ampul

There are a handful of Restek reference standards that are solids, where the composition is based upon % by weight. In the case of these standards, only 50 to 100 mg of material will be present in the ampule. This small volume will appear as a film or a small pinhead size glob. Like the example below, there’s nothing wrong with those standards. It is only the small volume received. In this case, once snapped, you cannot pour.

small volume of reference standard in an ampul

In summary…… Pay attention to the information contained on the CoA. Follow the storage conditions. Examine the vial and its contents prior to use. Make sure all components are in solution. Have the solution in the bottom half of the vial to aliquot or transfer. Finally, accurately measure all of your aliquots. Don’t just snap and pour.