Introduction

It has been known for several years that chemicals (e.g., BPA and phlalates) can leach out of the plastic, such as toys and baby bottles. The impact of these chemicals on human health is well known. Recent scientific reports have now noted that chemicals used in the manufacturing of disposable plastic labware, such as slip agents or plasticizers, can leach out of the plastic and affect laboratory experiments leading to erroneous results.^1-4

What comes out of your tubes

During incubation (e.g., enzymatic assays at 37°C or DNA denaturation at 95°C) chemicals used in the manufacturing process can leach out of the plastic and contaminate your sample.3 Figure 1 shows the absorbance spectra of water after incubation in tubes from several different manufacturers. As you can see, in contrast to other brand tubes, the water incubated in Eppendorf tubes (blue line) shows no significant UV/VIS absorbance. This suggests that no UV/Vis active substances are released from the tube into the water. This is one of the examples of Eppendorf’s commitment to minimize sample contamination. Besides highly automated manufacturing under clean-room conditions and purity testing of each production lot, Eppendorf doesn’t use any slip agents, plasticizers, or biocides during the tube manufacturing process (certificate upon request).

The next question to ask is how does leaching affect my experiment?

How the type of tube can affect your assays

It has been shown in several publications that the chemicals used during manufacturing of plastic consumables can affect assay results from DNA quantitation3 to enzymatic assays.1,2 In a Science paper from 2008, researchers showed that chemicals released from plastic tubes inhibited the activity of human monoamine oxidase-B (hMAO-B).1 Important to note that the researchers used an amber-colored Eppendorf tube in that paper. When they switched to a clear Eppendorf tube, the results showed an absence of significant inhibition of hMAO-B.2 Another important example is mass spectrometry. In a 2010 paper, researchers showed that Tinuvin-622 leaches from laboratory polypropylene and interferes with mass identification after MALDI-TOF.5 Another common lab application is sample concentration. When samples need to be concentrated, it is common to use a vacuum concentrator to accelerate the evaporation of aqueous solutions. Figure 2 shows how incubating water in different brands of tubes can affect the evaporation rate of water. Samples incubated in Eppendorf tubes had the highest evaporation rate, consistent with the data shown in Figure 1. Both of these experiments and the Science paper lead you to the same conclusion: If you have a leachate you never know where it will affect you.

Figure 1. Chemicals released from different brands of 1.5mL tubes can contaminate your sample. Shown are UV absorbance spectra of pure water incubated (30min, 95°C, 1,400 rpm mixing) in tubes from different manufacturers.

Figure 2. The brand of tube can affect evaporation rates. Chemicals, for example oily slip agents, released from the tube plastic can slow down evaporation. Some of these slip agents (e.g., oleamide) have also been shown to negatively affect the outcome of biological tests like enzyme activity or receptor-binding assays.1,2,4 Shown are the evaporation volumes (in grams of water) after 3 h incubation in a vacuum concentrator. Pre-incubation for 1 hr at 70°C.

Conclusion

Not all tubes are created equal. If a chemical leaches out of the tube, it can carry over to all of your downstream applications and you will never know when it might affect your assays. One good summary on the importance of leaching comes from Reid et al. (2009): “There are several steps researchers can take to minimize the likelihood of their data being compromised by leachates. Some manufacturers provide information on the additives content of their plastics; for example, Eppendorf use virgin polypropylene for their colorless pipette tips and microfuge tubes, and no slip agents or other additives are present. Although the associated costs may be slightly higher, researchers should purchase plastic ware from a manufacturer that does not use additives and avoid buying from suppliers that refuse to confirm the absence of additives.”²

References
1. McDonald G.R. et al., Science 322, 917 (2008)
2. Reid G. et al., GIT Laboratory Journal 9-10, 2-4 (2009)
3. Lewis, L. K. et al., BioTechniques 48, 297-302 (2010)
4. Watson J. et al., J Biomol Screen 14(5), 566–572 (2009)
5. Sachon E. et al., J. Mass. Spec. 45, 43-50 (2010)

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