Plastic storage tubes are used in laboratories worldwide to store biological and chemical samples, the most typical resin used is Polypropylene. There are many types and grades of polypropylene that are selected either on cost, molding properties or specific attributes such as binding and working temperature range.
Sample storage tubes can be supplied sterile, pyrogen – and DNAse/RNAse-free and it is generally accepted that this guarantees product integrity.
Few researchers ever consider that despite these apparent guarantees, plastic ware can still provide a potential source of error.
Most if biobanking applications require a clean product, free from sources of possible contamination that may impact the sample, users often confuse a requirement for a “clean” product with one that is “sterile”.
Sterilisation is a post-production process to ensure that there are no viable organisms present, it is no indication of the cleanliness of the manufactured part and is often used to mask any potential contamination that may occur during the manufacturing and assembly process.
During the manufacturing process various additives may be used to aid the molding process, often decrease the cycle time and lower the cost, these additives can be the cause of possible contamination, these include catalysts, flow agent, mold release agents and others.
Evidence shows that bioactive compounds can diffuse into solutions that come into contact with the surface of the plastic 1,2. These compounds, typically referred to as “leachables” or “extractables”, are used during the manufacturing process to improve product stability and durability. However, these compounds can have a significant impact on scientific experiments and pose a likely source of error in many assay systems and impacting reproducibility. Examples of leachable interference include inhibition of enzyme activity and falsification of nucleic acid quantification.
Definitions:
“Leachables” – Compounds that leach from a closed container into a sample as a result of direct contact.
“Extractables” – Compounds that can be extracted from a closed container when in the presence of a solvent.
The determination of extractables by GC/MS with ethanol as a solvent is a practical and reproducible way to determine the extractables that could leach from the resin when the sample is in long term storage and prolonged contact with the sample storage container/tube.
Since leachable compounds from plastic resin can have an adverse and erroneous effect on scientific investigations, it is vital that the performance characteristics of the storage tube are carefully considered for long-term storage of biological and chemical samples.
Sadly it is often the “price per tube” that is the critical determining factor in labware selection, however it is important to remember that your sample is going to be in contact with the resin of the tube for the life of the sample, this can be in excess of 30 years and once your sample is in the tube it is very unlikely that you can ever change this.
It is common practice to use adhesive labels on tubes, particularly for older legacy samples acquired prior to the introduction of 2D coded tubes, however Leachables are known to pass through PP resin from acrylic based adhesives and into the sample within.
A 2D (tube base) and Linear barcode laser etched on the side of a PP sample tube free from leachables can ensure no risk of leachables from either an adhesive label or the tube itself. Furthermore, the coding ensures the unique ID of the sample for complete traceability.
Other sources of possible contamination can include the use of silicone material used as a gasket in the cap, inkjet printed markings on the side of the tubes and poor sealing performance of any capping method used.
By Robin Grimwood, VP & General Manager at Brooks Life Sciences, a division of Brooks Automation Inc
References
- Olivieri, O.S.Degenhardt, G.R.McDonald, D.Narang, I.M.Paulsen, J.L.Kozuska and A.Holt.Can.J.Physiol.Pharmacol. 2012; 90:697-703.
- McDonaldGR, HudsonAL, DunnSM, YouH, BakerGB, WhittalRM, MartinJW, JheA, EdmondsonDE, HoltA.Science 2008;322(5903):917.
- Risk mitigation strategies and documentation for extractables, leachables and interactions in PFS, Carsten Worsøe, Principal Scientist, CMC Analytical Support, CMC DP Development, Novo Nordisk A/S, Qepler, Berlin, Germany. October 15-16, 2019
