How safe are your samples?

We often assume that once a sample is in a tube, it is safe. However, the physical and chemical properties of your storage tubes can introduce significant errors into your research. Here are three critical factors regarding sample integrity that every researcher needs to know :

1. The invisible threat: leachables and extractables
   Many researchers do not realize that plasticware can be a source of experimental error due to bioactive compounds diffusing into samples. Manufacturers use additives to improve product stability, known as "leachables" or "extractables," which can inhibit enzyme activity and falsify nucleic acid quantification. In a comparative evaluation using ethanol as a solvent to simulate extraction, Azenta external thread tubes were tested against competitor tubes. The results were striking: Gas Chromatography/Mass Spectrometry (GC/MS) analysis detected various dissolved substances in competitor tubes, including Pentadecane and Benzaldehyde, while Azenta external thread tubes consistently produced no detectable leachables, ensuring that the tube composition does not interfere with the scientific integrity of the sample.

   
   

2. The physics of freezing: volume and pressure
   Selecting the right tube requires more than just looking at the "nominal volume". Biological samples with high water content expand by approximately 9% when freezing, which can lead to catastrophic cracking or cap failure if the "working volume" is exceeded. This is why calculating the safe storage volume is vital:
   
   • Pressure buildup: as samples freeze, the air in the headspace shrinks while the sample expands. If overfilled by even 5%, internal pressure can pop the cap of the tube.
   • Thread design: external thread tubes maximize the internal volume for a given height, often accommodating more sample than internal thread designs because the cap does not ingress into the tube.

   • Freezing method: controlled rate freezing prevents "ice plugs" from forming at the top of the tube, which force expansion outward and damage tube walls.

     
     

3. Seal integrity: stopping evaporation and contamination
   Long-term storage presents two major hazards: evaporation and cross-contamination. If a seal fails, either through mechanical flaws or poor design, aqueous samples can evaporate or cross-contaminate, rendering irreplaceable samples unusable.

   Azenta subjected their tubes to rigorous vacuum and pressure testing to measure seal integrity.

   • Evaporation rates: in a one-month weight change test, traditional internal O-ring caps showed significant evaporation, whereas Azenta’s new external caps and internal co-molded caps showed negligible change

   • Burst pressure: due to the larger headspace, external thread tubes generate lower internal pressure during freezing, offering superior protection against bursting compared to traditional designs.

Ultimately, the safety of your biological and chemical samples relies on more than just the temperature of your freezer. By understanding the risks of leachable compounds, calculating true working volumes to account for freezing expansion and utilising advanced sealing technologies, you can prevent sample loss and ensure the integrity of your biological samples. Read the full white paper to discover why Azenta external thread tubes offer a superior solution for the long-term storage of your precious samples.