When learning that you may be transitioning to a newer revision of an EPA method some thoughts may come to mind such as: it took so long to perfect this sample preparation method, or I hope they have some improvements and or greater flexibility allowances in this revision. Well, that is exactly what we will touch upon in this blog post - sample preparation improvements.
If your lab is fast-tracking towards implementing EPA Method 525.3 then there are a few changes that you must be aware of. Hold on, I know you might be thinking: do I need to change everything I am doing currently? In some areas, yes, but the changes are all improvements that have been proven by real-world labs with their feedback. This critical feedback resulted in much more flexibility and improvement throughout the method revision - from sample preparation to sample analysis. This method revision is cost-effective and straightforward for commercial labs and is also more robust than EPA Method 525.2.
We will jump right in and start at sample collection. Some changes could impact the overall process. I would call them improvements since method 525.3 no longer uses sodium sulfite and hydrochloric acid. The preservatives now are all in powder form which will increase the pH to around 3.8. This in turn will provide a wider range of analytes to be extracted out of the sample in one extraction vs method 525.2 which states that separate extractions may be needed with certain analytes.
So how can pH alone contribute to the extraction success of such a wide range of analytes? This is due to another improvement with 525.3 that is replacing the C-18 sorbents with a newer polymeric sorbent. With this improvement, you now have the flexibility to use solid phase extraction disks (47 mm) or cartridges (6 mL). Each option has its place. The SPE disks used with styrene divinylbenzene (SDVB) can extract a wide range of semi-volatile compounds at a very fast flow rate. I like using the SPE 47 mm disks as they can process any type of drinking water sample very quickly and efficiently, especially with automation. I will use the 6 mL cartridge format if sample turnaround time is not a factor since the sample loading rate is limited to 10mL/min. If you do load at a faster rate, you will most likely have analyte breakthrough and sample to sample inconsistency. This will result in you having to do a re-extraction , and no one wants to go through that. My advice is to choose the right SPE media format and extraction platform for your lab’s workflow. If your analyte list includes dimethipin I would recommend using modified polymeric media as stated in EPA method 525.3 section 13.2.1. This analyte did not meet method acceptance limits when it was extracted with SDVB media. Why take a chance of not passing if you have this compound in your analyte list? Method 525.3 allows this flexibility option. These SPE media improvements will ensure recoveries are well within limits to provide quality data for your customers.
Internal Standard Additions
Another improvement I was glad to see is the internal standard (IS) addition. With method 525.3 you will now add the internal standard to the final extract not in the sample prior to extraction as stated in 525.2. I was glad to see this change as I felt that the addition of the internal standard to the sample normalizes the data and accounts for all losses without the impact when the IS was added prior to extraction. So why is this an improvement? You will have improved quality that will demonstrate the losses throughout the sample extraction, drying and concentration steps. This means you need a more robust sample preparation procedure and I prefer to use an automated system as much as possible. By implementing automation throughout the 525.3 procedure, you limit the manual interactions with each critical technique and in turn, create consistent results throughout the sample batch which will make being within your method limits that much easier.
I hope you have enjoyed learning a few of the overall method improvements for EPA method 525.3. If you would like a more in-depth look and knowledge of even more real-world situations concerning interferences, phthalates, drying agents, problem compounds known potential problems with 525.3 and how to avoid them then please sign up and view my webinar on EPA 525: Modern Sample Prep Solution for Drinking Water Labs.