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by Victoria Miller, Senior Scientist
Mass spec results can be compromised in many ways; everything from the detergents used during extraction and solubilization to the chemical grades of the solvents during the analysis can impact the results.
Polyethylene glycol or PEG is one of those contaminants that can sneak up on you in unexpected ways. The only ‘good’ thing about a PEG contamination is when it’s there, you know what it is. That pesky +44 Da repeat is not what anyone wants to see in a chromatogram- unless of course, you are studying PEG!
The problem with PEG is you can find it just about anywhere! When I first started learning about sample preparation in the mass spec world, I had no idea just how easily PEG could work its way into your sample. The following is a summary of the information I was able to glean from the interwebs. There is a plethora of good advice out there on the web, from people more experienced in mass spec than I am, and I hope my summary will help you progress on your mass spec journey.
A potential source of PEG is the solvents used for the analysis. Do not store (or buy!) solvents in plastic bottles for mass spec analysis. PEGs and other plasticizers can leach out into the solvent and emerge in your chromatogram. The same rule the bottles used to load your solvents onto the LC-MS, again, don’t use plastic bottles, and more importantly, when washing the glassware to measure, mix and store your solvents, don’t use a PEG-containing detergent, or at very least, rinse the glassware with a really hot water wash, then rinse with an organic solvent prior to using it.
Triton X-100 and NP-40 (and its substitutes) are PEGylated detergents that should be avoided during protein extraction. We are confident that we can remove SDS from your sample, and encourage you to see what SDS can do for your extraction protocol.
PEG can enter your workflow at many stages. Syringe filter units could be a source, as could any membrane used for concentration. If suspicious of your membranes, rinse 2-3 times with deionized water to remove these contaminants. Some pipette tips and microfuge tubes may release PEG, especially if used for aggressive solvents. Many personal care items, including hand creams, contain PEG, if only in trace amounts. Be sure to wear gloves when handling anything that will go anywhere near your samples. Consider having glassware dedicated for only mas spec solvent preparation. If you do in-gel digest, have a set of gel staining dishes just for mass spec experiments. This will also help avoid keratin contamination.
Here at the R&D lab at Proteoform Scientific, we are working on an adaptation of the ProTrap XG that may be useful for PEG removal. If this is something you’d be interested in hearing more about, drop me a line at firstname.lastname@example.org.