I am willing to bet there have been a few people reading this that early in their careers have had a moment of “what does that mean” when learning new procedures and or methods. You are about to learn mine. When I was onboarding and learning new standard operating procedures and methods one really stood out and still does to this day. It was when I was first exposed to EPA method 1664B. It stated right in the introduction it is a performance-based method. I thought to myself what does a performance-based method consist of and how do all labs qualify to run it?
Well I went on and read the entire EPA method for 1664B. This method went ahead and described all the guidelines and explanations for what it means for a method to be performance based or rather a “Performance-Based Measurement System (PBMS) & Flexible Approach” as they call it since 1997.
So what are “performance-based measurement systems” or a “flexible approach”?
This type of methodology, simply put, is when a laboratory can make their own modifications to the entire sample preparation procedure as long as their quality control (QC) samples pass the guidelines outlined within the method being followed. This includes extraction, extract drying and evaporation steps. It is very important that the laboratory does not fall outside the quality control limits (without obtaining other necessary permits) when following a performance-based method. You must be able to prove that the entire sample preparation procedure you are following works as it should without sacrificing recovery or violating the provisions made within the method itself.
For instance, with SW-846 test methods like 8270D or 8081B, instead of following the liquid-liquid extraction (LLE) procedure, you have the capability to use solid phase extraction (SPE). As long as you can prove the modification meets all the quality control criteria outlined within the method of choice in your lab, then you have the ability to utilize that allowable method modification.
In addition to being able to use SPE for methods like 8270D, 8081B and 1664B, you also have the option to deviate from using sodium sulfate. WHAT?! Yes! I know we all really “enjoy” dealing with sodium sulfate, but there are better drying options out there…I promise. For instance, you can use a solvent phase separation paper which is a hydrophobic membrane that allows non-polar solvents through, leaving the water from the sample extract behind on top of the paper. This is a real time saver because you don’t need to bake the separation paper, nor does it need to stay out and allow the residual solvent fumes to evaporate for hours on end. That is the beauty of these performance-based methods! So long as your QC passes under all the requirements outlined in the method, you are good to go to make modifications to the procedure.
Now that you know what a performance-based method looks like, how does that differ from a prescriptive method?
The answer is somewhat in the name. Prescriptive methodology is like a dictation that a laboratory must follow and may not go outside the guidelines or procedure unless the procedure has allowable modifications as such. These are like your 500 series drinking water methods or 600 series wastewater methods. For instance, if the method does not say anything about being able to use SPE or automation, then you cannot use SPE or automation. However, like most instances, there are other avenues that can be taken to allow for more flexibility with these methods. If you follow the ATP procedures, then you have the option to make modifications as such. However, these procedures are time consuming and cost a lot of money, so it is not as appealing to make modifications to these types of prescriptive based methods.
So, to sum it up, even though the performance-based methods are much easier to work with there was a main goal in mind for this approach. The EPAs intention with this approach was to reduce the cost of monitoring and stimulate the development and use of innovative technologies. This in turn would also speed up the introduction of new methodologies to be produced. This approach had an end goal for the EPA to be able to improve the quality of monitoring science for our nation. For this I am grateful as science is always evolving with new techniques and innovative technological advancements that can be a real lifesaver for laboratories.
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