Questions & Answers from the live event
What are some of the other examples of contamination in the laboratory environment that could potentially contaminate my samples?
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, pipettes, and 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 experiment with.
If you have done everything that is obvious, then look for some of the non-obvious answers; things that may just be in the room. We had an experience in a lab where a doorstop was the reason for airborne contamination that caused problems with getting some low levels of lead in one of our samples. That was not something we would even consider, but it was happening. You must take a very large view as to what could potentially be around that may affect your samples.
How do you avoid carryover or contamination of plasticware from one analysis to another?
The easiest way to avoid carryover contamination is single-use consumables. Using disposables ensures that you will not have carryover because you do not have to reuse. If you are not able or do not wish to use disposable digestion containers, you will need to develop a cleaning method for your supplies.
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 should give you clean equipment.
Do you recommend acid washing the single-use plastic labware prior to use to help minimize metal contamination?
If you are getting our digestion cups or the filters (FilterMate® or FlipMate®), 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 can get shipped from a manufacturer is nearing the limit of what can be clean because of the things that it touched between the manufacturing and shipping to you. What you can do is an analysis of the materials that you get before using them.
If you have something that has certification limits on it, then you can use those to see if they meet your needs. Otherwise, you would need to do a batch analysis and get a statistically relevant number of pieces of those products to analyze. If the limits do not match your needs, it may be that you need to do treatment prior to using those supplies in your digestions.
When would I use the Ultimate Clean™ cup versus the UltimateCup® cup? And what are the main differences between the two products?
We can use iron as an example. Iron is one of the common minerals with a detection limit of 100 micrograms per liter in our UltimateCup cup, and 25 micrograms per liter in our Ultimate Clean cup. It is about deciding what levels are going to be acceptable for you, your customer, your clients, and the reports you must generate.
When we designed these products, our initial thoughts would be that the Ultimate Clean cup would be a specialty cup used for projects where something needed an extra cleanliness level, and the UltimateCup cup would be for your general everyday use.
Can you describe a standard method for metal digestion in soil with minimum interference?
The digestion methods, generally, are not going to be the source of your interferences. It is 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, there must be 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 are looking for. If you are 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 is more of the sample matrix that you need to be concerned with when you are addressing your interferences.
How does the choice of reference standards affect your ability to achieve lower limits of detection?
It is 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 would 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, at those levels, every time? That is something that an outside standards provider can do. Do not 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 will help you decide what you need from your standards provider in helping you to get the detection limits that you need.
How can we achieve a better limit of detection?
To consistently achieve your low detection limits with the instrumentation you have, you must be diligent in monitoring all the different pieces of equipment, your digestion equipment, and the transfer steps in between digestion analysis. Be hypervigilant about maintaining the consistency of them and keeping them clean. 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.
Do you have digestion cups made from PTFE?
We do not have digestion cups made from PTFE, but we do offer cups made from perfluoroalkloxy alkane (PFA). This material is a fluoropolymer, like PTFE, but is more rigid and durable. These cups are not intended for single use but should be cleaned and reused after each digestion.
How do you assure the quality of the certification of your equipment?
We have an extensive testing regime in place to ensure the highest quality product is supplied to you. Each lot of raw materials is tested prior to being put into production. We utilize an ICP-MS for metals screening, and it follows QC procedures like what is in place in most environmental labs. Additional quality checks are done with each production lot to look for potential defects in molding or manufacturing.
It would be interesting to know differences of contaminants without caps with watch glasses and with reflux caps. One competitor for digestion vials uses a flip top cap, where the cap is hinged and folded over (not completely) to allow some refluxing. It would be nice to see how or if that is affecting results and what methods are the best?
We are familiar with those cups with the attached lid and offer them to purchase on our website. While we do not have any data comparing the reflux action of those cups with a separate reflux device such as a watch glass, we can speculate based on the physical configuration. Refluxing works best with a surface that actively directs the condensing vapors back into the heated mixture. Having a concave-down surface, like the watch glass previously mentioned, allows the condensing vapors to collect and drip towards the center of the vessel.
