Metals digestion detection limits: How low can you go?

With the rise in industrial products and processes, we have seen a dramatic increase in the amount of electronic waste in our landfills over the past few decades, and as a result, a significant upsurge in hazardous leachates and heavy metals accumulation in our environment, ecosystem, and food chain.

Heavy metals are not naturally biotransformed, so they continue to persist in our surroundings. Several safety and regulatory limits have been established to monitor and manage their presence in soil, water, food, and feed; and testing is used to substantiate environmental safety. Antylia Scientific™ and Environmental Express^® have established a range of inventive solutions for clean and safe metals digestion.

In this on-demand SelectScience^® webinar, Nassima Galloway, EMEA sales lead with Antylia Scientific, Michael Bechtold, global product manager at Environmental Express, and David Smith, technical director at Environmental Express, show how you can automate parts of your workflow, save time, and obtain accurate metals detection data by incorporating these tools into your workflow.

Read on for highlights from the live Q&A session or register to watch the webinar at a time that suits you.

Q: What are some of the other examples of contamination in the laboratory environment that could potentially contaminate my samples?

DS: Anything and everything, to be as broad as possible. There are a lot of different pieces and parts that you might not think about, gloves, dust in the air, the pump tubing that introduces your samples into your analytical equipment, your pipettes, digestion reagents. Everything that is around is a potential source of contamination. Whether it is going to contribute enough to affect your samples is something that you may have to do a little bit of experimenting with.

If you've done everything that’s obvious, then look for some of the non-obvious answers, things that may just be in the room. I’ve had experiences in a lab where a doorstop was causing some airborne contamination that caused problems with getting some low levels of lead in the sample that we were working with. That wasn't something that we’d even consider, but it was happening. You must take a very large view as to what could potentially be around to affect your samples.

Q: How do you avoid carryover or contamination of plasticware from one analysis to another?

DS: The easiest way to avoid carryover contamination is single-use consumables. Being able to utilize single-use ensures that you will never have carryover because you don't have reuse. Obviously, there are some concerns with that.

The best way to adapt your cleaning procedure is to use something that mimics the digestion process that you have. Most of our common digestions use some combination of hydrochloric and/or nitric acid. Utilizing that on your supplies prior to doing your digestions will give you the best chance of removing the things that those digestions are designed to pull out. Basically, just doing a rinse of your supplies prior to use with the acids you would be using in your digestions.

Q: Do you recommend acid washing the single-use plastic labware prior to use to help minimize metal contamination?

DS: If you are getting our digestion cups or the filters, the Filter Mate, or the Flip Mate, we have done our best to provide what is both economical and practical to get a naturally clean product to you.

We are getting to the point where what you're able to get shipped from a manufacturer is nearing the limit of what can be clean because of the inevitability of things that it had to touch between the manufacturer and getting to you. We're almost at a floor of what you can get for cleanliness. What you can do is a locked analysis of the materials that you get before using them.

If you have something that has certification limits on it, then you can utilize those to see if they meet your needs. Otherwise, you would need to do a batch analysis, and get a physically relevant number of pieces of those products. If the limits don’t match your needs, it may be that you need to do some treatment prior to using those supplies in your digestions.

Q: When would I use the Ultimate Clean Cup versus the Ultimate Cup? And what are the main differences between the two products?

DS: I'll use iron here as an example. Iron is one of the common minerals with a detection limit of 100 micrograms per liter in our Ultimate Cup, and 25 micrograms per liter in our Ultimate Clean Cup. It’s about deciding what levels are going to be acceptable for you, for your customer, your clients, for the reports that you have to generate.

When we designed these products, our initial thoughts were that the Ultimate Clean Cup would be for those special projects that you have, something that needs that extra cleanliness level — a specialty cup — with the Ultimate Cup being just your general everyday use.

Q: Can you describe a standard method for metal digestion in soil with minimum interference?

DS: The digestion methods, generally, are not going to be the source of your interferences. It's going to be everything else that is in your sample that really has to do with the interferences. Most methods have ways to address it.

For example, if organic compounds are a problem with your analysis methodology, they've got different ways to address those — usually peroxide, or excess nitric acid, to break those organic compounds down, different combinations of your acids depending on the metal that you're looking for. If you're looking for some of the more refractory metals, then you may have to utilize something along the lines of hydrofluoric acid, which obviously has its own specific safety concerns. It’s more of the sample matrix that you have to be concerned with when you are addressing your interferences.

Q: How does the choice of reference standards affect your ability to achieve lower limits of detection?

DS: It’s mostly dependent on the competency of the preparer, whether that is you, your technicians, or your outside provider. Obviously, if you were doing this yourself, you'd have complete control over what you were working with. And ideally, your people will be able to do exactly what you want and know exactly how to prepare it according to your specifications.

The downside of that is do you have that time, and can you consistently make it the same as those levels every time? That’s something that a standards provider can do. Don’t be afraid to ask your standards providers the hard questions. Ask about their quality control practice or how they respond to potential problems. Those are the kinds of things that'll help you decide what you need from your standards provider in helping you to get the detection limits that you need.

Q: How can we achieve a better limit of detection?

DS: To consistently achieve your low detection limits with the instrumentation that you have, you just have to be diligent in monitoring all the different pieces of equipment, your digestion equipment, the transfer steps in between digestion analysis. Be hypervigilant about maintaining the consistency of them and keep the cleanliness. When you identify the process that gives you the results you need, put them into a procedure, and make sure that everyone working with those samples understands it.

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