If you are processing environmental samples then you’ve probably dealt with contamination at some point. If you haven’t, then you should be congratulated for creating the only laboratory on Earth that has ever been completely free of all sources of contamination!
There are many (in some cases, many many many) sources of contamination and the severity of your contamination issues can vary significantly depending on what types of samples you run, the cleanliness of your laboratory, the systems that are running, and the care with which samples are being collected, stored, prepared, run and disposed of.
Depending on the specific applications you’re running in your laboratory, you may have contamination issues that pose little or no impact to the quality of your data. For example, if you’re processing samples against EPA Method 537.1, you’re focused on quantifying perfluorinated compounds (PFCs) and probably won’t care (or notice) contamination from bis(2-ethylhexyl)phthalate. Likewise, if you’re processing drinking water samples and you’re focused on the target analytes in EPA Method 525.2, you probably won’t be bothered by contamination from a perfluorinated compound like PFOA.
Where do all of these contaminants come from? That’s easy to answer – they come from everywhere!
Some of the more common sources of contaminants include: solvents, solvent and sample bottles, technicians and poor laboratory technique. Even the air can contaminate your laboratory.
It’s impossible to eliminate all sources of contamination, but you can reduce the contribution that each source makes. Let’s use your solvent selection as an example. When choosing my solvents, I always select those that match or exceed the requirements for my method. For more information on this, check out my recent blog post on selecting the right solvent grade.
People themselves can cause contamination. Using lotions or perfumes can make your skin soft and make you smell like a celebrity, but these products can be a problem. They can have phthalates, BHT, fatty acids, and oils. It is easy to imagine a scenario where some extra lotion on one hand transfers onto my lab glove as I try to put it on – instant contamination! This is why I avoid using these types of personal products when I am in the lab.
Poor technique can be a significant source of contamination, made more complicated because it comes in many forms. From improperly cleaning lab supplies to poorly rinsing glassware, to forgetting to clean syringes in between uses, to using dirty work surfaces, contamination can come from many sources. It’s also important to use labware that’s compatible with all of the solvents that it will come into contact with. For example, using methylene chloride with labware made from the wrong plastic material could produce a solvent interaction which extracts a number of compounds into your blanks, standards and samples.
The air (or more commonly, the dust in the air) can cause contamination as well. Dust can carry various chemicals and the flow of a hood can pull those particles into the hood and deposit them into your extraction. It is always a good idea to make sure that your work area is as free from dust and debris as possible. Read our previous post more on contaminants in the lab.