How “Easy” Sample Preparation Can Hinder Our Progress

Allen Misa-Food and ENV Marketing Manager

Everyone—and I mean everyone—would love to simplify their sample preparation. The goal of sample preparation is to make things faster and easier, to increase precision, to use fewer resources, but still obtain the most accurate results possible. This is exceptionally prominent in food testing laboratories because of the endless combinations of analytes, sample types, and matrix interferences that can greatly complicate the analytical process. The majority of food labs that I talk to attest that their greatest challenge is sample preparation.

Since the start of chromatography in food testing, there has been an extraordinary evolution in sample preparation.  Beginning with weighing and dilution and moving towards Solid Phase Extraction (SPE), there is a well-defined hierarchy of sample preparation techniques. This hierarchy has proven to be a good depiction of the level of selectivity and cleanliness associated with the technique in association with method difficulty.

Characteristically, the more selective and cleaner a sample prep method becomes, the more “work” or technical challenges the method may present. Therefore, for successful method development, those methods further up in the hierarchy require that analysts possess, and apply, more knowledge and experience in separation science.

In the food industry, although SPE is the cleanest and most selective preparation method (and can be readily automated) its widespread adoption has been hindered by the popularity of a simpler, but less effective technique.  Many laboratories have adopted the QuEChERS technique due to its claim of Quick, Easy, Cheap, Effective, Rugged and Safe extractions.  The method is certainly easy to use, easy to learn, and is straight forward if one uses the prescribed methods. It is also relatively quick and sufficiently versatile to tackle many of the common cleanup needs for residues in many food samples.

However, the widespread adoption of this method has been strongly driven by the industry trend of using standard commercial kits so that analysts can pump out samples at the highest rate possible with the resources available. I must admit that QuEChERS is a great method and has gained a lot of popularity because of its advantages.  However, please entertain me when I say that in many cases the simpler and easier nature of QuEChERS is actually hindering the ability of laboratories to produce reliable results. While offering the temporary advantage of a quick, easy, cheap, effective, rugged and safe method, the primary goal of accurate results can too easily be compromised.

For example, I recently spoke with the manager of an agricultural testing laboratory that routinely uses QuEChERS for analyzing pesticide residues in produce.  Like many agriculture labs, they use a suite of tests to process a wide variety of sample types for a wide range of contaminants.  They have adopted several QuEChERS methods which their analysts run on a daily basis, using pre-made kits from various manufacturers.

I asked the manager, “What are your primary challenges?”  I was surprised to hear that analysts struggle to understand the technical troubleshooting knowledge.  “Why is that?”, I asked.  He responded by saying that the scientists have become so conditioned to using prepared QuEChERS kits and pre-designed methods that when an analytical challenge arises they immediately blame the kits instead of thinking about the possible reasons for error and perhaps modifying their approach to improve the method.  They have been so conditioned to believe that product “A” will do everything they require that when it doesn’t, they immediately search for Product “B” to solve their problem. This search for a magic, pre-packaged solution has replaced the time-proven, scientific approach of troubleshooting the method. Ironically, the troubleshooting solution to the above problem was simply to reduce the SPE sorbent mass quantity provided in the dSPE kit. The sorbent was extracting too well, thus also removing the analytes of interest.

You can say that this phenomenon could happen with any analytical method. However, it is just too easy to bypass the science when running QuEChERS because of its methodical, simple, step-by-step nature.  With SPE, the scientist running the method must understand beforehand what the method is doing and what type of chemistry is taking place.  This is because SPE, by its nature, is a more complex technical process where a sample is introduced to a media which first interacts with the target analytes and then specific solvents. Buffers are then used to wash out interferences and finally elute out the targeted analytes.

Although similar performance challenges can come up with SPE, the fact that it is not a kit packaged product (implying a “plug and play” method) motivates the analyst to understand the science that is taking place in the method and to really know what is going on in each step. Therefore, when a challenge does arise, the analyst is able to use that scientific knowledge to intelligently troubleshoot the method and make modifications on the existing product without reflexively looking for another kit.

I understand that there will be some who will disagree with the above assessment, but this is not an isolated anecdote; I have frequently heard of this occurring in other laboratories. We seem to be entering The Jetsons era where pushing a button does everything we need. QuEChERS leads us in that tempting direction by providing us a magic “plug and play” kit to solve all our sample preparation problems. And, just like the lesson that we learn from The Jetsons, when we become so accustomed to pressing that button, when the button doesn’t work, you find yourself no longer knowing how to perform the task.

I believe that there is more to chemical analyses than just pushing the red start button on the instrument—you still need to understand the underlying science. However, I am sure there are many other observations and opinions out there that would either support or refute this opinion. So, please feel free to share your opinions and experiences.

In doing so, please bear in mind that Phenomenex offers all kinds of sample preparation applications, products, and techniques—including QuEChERs! Our goal is to ensure that the analyst is provided the best tool for the job, not just the most convenient.

To learn more about different sample preparation options for food samples, download our Food Sample Preparation Guide.