Follow along with our experts as they dive into the ICP Operations Guide, chapter by chapter. In this accessible transcript of Episode 3, "Handling, Calculations, Preparation, and Storage of Standards," we present the collective wisdom of our in-house experts—Host and Technical Director Mike Booth, Production Manager Thomas Kozakowski, Technical Support Chemist Ashley Jones, and Technical Product Manager Dr. Lesley Owens.
The dialogue covers crucial practices for handling chemicals, the impact of temperature on standard preparations, and the intricacies involved in the preparation and storage of standards. You can listen to all episodes of Bench Boost on your favorite streaming platform!
Mike: Hello, everyone. Today I'm joined by one of our Production Managers, Thomas Kozakowski; Technical Support Chemist, Ashley Jones; and Dr. Lesley Owens, our Technical Product Manager. We're going to continue with a deep dive into one of our most popular resources: our ICP Operations Guide, written by our founder, Dr. Paul Gaines. Make sure to tune in each week for more insights from this guide. Today our team will be discussing Chapter 3 on Handling, Calculations, Preparation, and Storage of Standards. If you would like to follow along with us, you can view the ICP Operations Guide on our website.
Handling
So, let's start off with Handling. Lesley, do you want to talk about pipetting from the bottle versus pouring back in the bottle? In essence, pipetting from a secondary container?
Lesley: Yeah, Mike. So, this is just generally good lab practice. So you never want to put anything into your standards container.
You're always going to want to pour into a secondary container. You want to make sure that secondary container is also really clean. You don't want to contaminate because of anything in that secondary container, then you want to do your transfer or your pipette from your secondary container. Then you're never going to pour that solution back into your stock bottle.
That’s also preventing contamination. So even though you want to save it, we understand that, but remember good lab practice. Don't put that back in there. Um, this is kind of similar to eating chips and dip with your friends, right? You don't want to double dip with your standards.
Mike: Exactly. I know sometimes it feels like it might not be much of an issue, but the second you get contamination, then you're going to waste a lot of time chasing that down.
Ashley, can you talk us through a little bit about the importance of temperature when preparing standards?
Ashley: Yeah, so I think we mentioned it in the last episode a little bit, but when you're working with standards in different climates and especially climates that are subject to major temperature changes, if you're swinging from really low temperatures into really high temperatures, you're going to see that effect on your volume.
And that's part of why we recommend weight preparation, gravimetric preparation. It's a little bit more reliable. You're going to be less likely to have to deal with those things. And then again, like we talked about in that last episode, your temperature is also going to impact transpiration. It's going to make it more of a problem. So keeping as good of a control on your lab temperatures as you can with the HVAC system, I think it's going to make a really big difference. It's going to make your life a lot easier trying to keep control on those standards.
Mike: Yeah. And we've talked in previous episodes about how HF is important. So, you know, there are a lot of standards, as you do sample prep, you're going to work with HF quite a bit. Thomas, can you review some of the conditions and handling when dealing with HF and especially when using glassware?
Thomas: When you're using glass, you're going to have problems with HF. I mean, even a little bit, you're going to have stuff leach out. So, I've done this kind of study before where we pour the solution into a beaker that's plastic and one that's glass and run a trace metals on it. All sorts of stuff comes out of the glass.
You'd be surprised what's in glass. It's not purely boron and silicon. Plus you might have some memory effects from anything else that's been in the beaker before. Glass pipettes are nice, but when you're using HF, you just can't do it. Sometimes we get those ampules from NIST that have the longer neck on them, they work great, but we can't do that for any HF solution. It contaminates it immediately.
Mike: Yeah, we've definitely seen that as an issue in the past before and we use a lot of calibrated flasks and things like that and introducing HF to those is just going to ruin your calibration.
Thomas: Yeah, over time it'll, it'll eat away at the glass enough that the calibration will be off and you'll be wondering why it's not what it should be.
We do volumetric densities here and you can see over time when you're doing HF ones that they go out of spec.
Mike: And Paul mentioned, in this chapter of the ICP operations guide, a little bit about how best practice is to use a stock standard solution for one year. Lesley, can you go into a little bit more details as to why the one year time frame is specified if the solution is chemically stable?
Lesley: Yeah, so this is more of an issue with transpiration than it is chemical stability. So from our TCT studies that are available on our website, you can see that repeated use of a standard will start to get into that range where you're going to go out of spec or outside of the uncertainty that we've put on the material.
The fill level of your bottle affects transpiration as well as the number of times you've opened and closed. We talked about temperature affecting transpiration - that can be an issue too. If you're not as regulated in your laboratory, you could have some issues there and just general contamination.
You run a risk the longer that you use a solution, the more likely you could contaminate in addition to the concerns with transpiration.
Mike: Yeah, that's a good point. I mean, we've seen contamination even in our lab. It can happen, you know, maybe a week after the bottle is opened and it takes a little while to find it, especially if it's something you're not looking for.
But the second you're looking for sodium in your zinc standard and it's contaminated in your stock solution standard, that just causes all sorts of issues, right?
Lesley: Environmental contamination is really hard to track down too. So you think you can be doing the right thing by doing your secondary container and never putting anything into your stock solution, but the environment's going to also cause problems with contamination.
Preparation
Mike: Exactly. Well, I think we've talked a good bit about handling. Let's move on to preparation. So I think one of the one of our favorite topics to talk about when it comes to preparation is preparing by volume versus preparing by weight.
Mike: So, Thomas, do you want to kick us off talking about that?
Thomas: Yeah, whenever you prepare by volume, you got to be worried about that density.
So as temperature changes, your density changes. Colder solutions are more dense and warmer solutions are less dense. And if you're preparing them in your lab, that can change as something equilibrates. When you actually fill a flask, and add acid and water to it, it gets really warm. The next day you come in, the volume actually goes down with that equilibration.
So that's something we always do when we make stuff by volume here at Inorganic Ventures. Let it go overnight, then bring it to volume the next day. Cause it does make a big difference. Making by weight is just more accurate. I mean, you've got a balance, you've got a number, it's tried and true. If the temperature goes up and down, the weight's really staying the same. As long as it's sealed, of course. You’ll have evaporation overtime, but it’s way more accurate with the weights.
Lesley: I'll add that you don't have to worry about viscosity issues. So you talk about auto pipettors - I think you're drawing in a certain amount of solution with that auto pipettor, but with viscosity, it could be vastly different than what you think you're actually pulling up.
Also air bubbles could cause problems when you're using an auto pipettor. You may not see that an air bubble was brought in, but when you dispense onto a balance, you would see that there is a discrepancy between what you think you pulled in versus what was actually delivered.
Mike: Exactly. That's a great point.
So we always stress, you know, just do the most accurate method that you can and the vast majority of the time, weight is going to be way more accurate than volume. So next up in preparation, let's talk about the difference in volume to volume versus absolute percentage of matrices.
Paul mentioned that when someone prepares by volume from volume, it may be 5%, but that's not the true percentage of say like nitric acid, for instance. Anyone want to take over on that one?
Thomas: Yeah, so in manufacturing our standards, we make something that's maybe 5% nitric. It's not 5% nitric because it's really 5% of a 70% nitric. So when you do the absolute of that, you just multiply that by the 0.7 to get your absolute weight of acid. And when you're doing stuff on the ICP, the differences do matter. Matrix matching is quite critical, depending on concentration levels and what kind of nebulizer you're using - that all plays into it.
HCl is the same kind of thing. A lot of stuff we do here is 10%. It’s really 10% of a 36% HCl. It’s pretty much industry standard. So if you see a volume to volume, it's really a volume of a volume.
Mike: Yeah, that's something that Paul provides a pretty good table in the guide of, you know, if you buy concentrated nitric or HCl, these are the percentages and what the density you should expect to see is.
I would say if you're really worried about the exact concentration, maybe just go with a molarity. We see that from time to time, right, Ashley and Lesley? People requesting molarity?
Lesley: Yeah, that's a good point. Even though the default for us is volume to volume from that concentrated material, we can quote and we can produce materials in either absolute or molarity. Those are common units that we get for the matrix.
Calculations
Mike: Yeah, definitely. Alright, let's talk calculations next. So we've already talked about the differences in preparing by weight versus volume. I would just throw out we have some people ask, “Hey, I only have this calibrated glassware by volume or I use a calibrated pipettor. How do I switch back and forth?” And really, I think the answer is density. We use density pretty much every single day in almost every calculation we do, right?
Thomas: Yeah, it's fair to say that absolutely everything that we certify at Inorganic Ventures is actually certified weight to weight. The NIST standards that we get, if you look at their certificates, they're usually milligram per kilogram is how they're displayed, but we'll do microgram per gram. It's really off by a factor of a thousand, as long as you get the units to cancel out properly, you're good to go. We apply the density and then put that on the certificate, because people are used to seeing microgram per mil or milligram per liter. Just keep in mind that density is at 20 degrees. So if you're working in a hotter lab, that density might actually be a little off, but you can always convert that to a weight to weight certified value. You're good to go. That'll work every time.
Mike: And I would say too, if you're questioning the density of something, you can always weigh this out in your lab. As long as you have a calibrated volumetric to measure volume. But I would recommend that you're not using a small volume. You would want at least one milliliter, I think a calibrated pipettor for one mL. The uncertainty on that is about the same as three place balance.
So they're relatively accurate, but you know, like Lesley mentioned, you do want to think about viscosity and look out for air bubbles. But that is a way that you can measure it in your lab so you can work with density if you don't have a density provided for you on a sample or something like that.
I know Thomas, you sort of mentioned some of the units we work with, you know, microgram per mL. So, people would talk about, parts per million or parts per billion, but those aren't really used the correct way. And I think that's the same for everyone.
Lesley, I see you smiling. Do you want to talk about that a little bit?
Lesley: Yeah, I'll take that one. So, you know, we assume we use ppm and microgram per milliliter interchangeably and that's technically incorrect. So ppm or ppb is going to be a weight/weight unit instead of a weight/volume unit. When you're talking about water density equals one, this is all the same.
It doesn't really make a difference. But when you start to get solutions that have different densities, then that becomes a factor. We typically assume ppm to be microgram per milliliter. We usually quote in the weight volume unit, but if you need that to be weight/weight, please specify that, and it's not a problem for us to produce material.
As Thomas said, the majority of our things are already certified as weight/weight. So it's not a problem for us to convert that back and forth, so that you don't have to worry about using the density and doing it yourself.
Thomas: It's actually easier for us to make stuff weight to weight cause we don't have to bring it to volume.
We don't have to wait for the time to let it equilibrate. It's actually a lot easier for us, but a majority of people are doing weight to volume.
Mike: That's correct. I think it's one of those things where people think they're just used interchangeably. They mean the same thing, but I think some of our more senior technical people have said it's really weight to weight but no one actually uses that.
So we'll know what you mean, but if you want, weight to weight, please request that specifically and we can handle that for you as well.
Storage
Mike: Let’s talk about storage. So Ashley, we have storage conditions listed on certificates of analysis for all of our products. But how would you recommend storage for just samples, standards, working standards, that sort of thing?
Ashley: First things first, capped - that's usually the best way to go. So that is something that tends to not happen in some cases we've seen. Making sure that your bottles are capped, you're going to avoid contamination, you're going to avoid knocking them over, it's going to help a little but with transpiration evaporation effects.
We talk a lot about our TCT bags. If you happen to have a heat sealer, that's great. We reseal our TCT bags for some of our things in house as well. But Thomas has talked about, I think in the last episode, that one of the best ways to avoid those transpiration effects, especially if you're going to keep your standard for quite a while, would be just to stick it in a fridge.
That's going to kind of negate that transpiration effect. You just want to make sure again, that you let it come to room temperature. You give it a good mix before you use it to make sure it's homogenous, but you know, making sure if you've got light sensitive solutions, that those are marked clearly so that you can see if they're not being stored properly. Keep those in complete darkness.
But generally speaking keep it in the fridge, keep it somewhere safe on the shelf where it's not going to be knocked over. It's not going to be contaminated and you should be fine.
Mike: Those are excellent points. Paul mentioned chemical stability, and we've talked a lot about that, especially in the first episode of the podcast. The majority of things are probably going to be chemically stable that you're going to run into, but it's all the things that we've talked about earlier in this episode about the handling.
The risk of contamination, all those things, you just want to make sure that it's probably not if your standard is off or you're, you know, if you're having issues with a specific sample set or a working standard, it's probably not a chemical stability issue unless you actually see a precipitate form.
It’s probably some sort of handling issue or contamination issue that you need to sort of run down and figure out.
Anyone else have anything they want to throw in on this chapter before we close it out?
Thomas: There is something else I thought about with actual storage. We have seen if you've got low levels of silver, you can have problems if you store your bottle near HCl over time. HCl can seep into your standard with what I would call it reverse transpiration – it contaminates your silver.
If it's low level, it'll precipitate and you can't see it. If it's higher level, you might see it, but it takes a lot of those fumes to actually get in there and, and cause problems. But if it's in an enclosed space, you're gonna risk it being much higher.
Mike: Yeah, that's a really good point. I mean, those environmental conditions can be make or break for achieving accurate measurements and results. So, you know, we've seen that in our lab areas where we work with a lot of concentrated acids. You'll see the corrosion happen in hoods and in metal shelving. That sort of thing needs to be replaced from time to time.
I know that Paul actually mentioned when the company was located in New Jersey, because they were located so close to the shore, they could see sodium seep into water if they left it uncapped over time. So they did time studies on that. I think there's a lot of environmental issues.
So, keep your lab clean as clean as you can get it and I think that'll solve a lot of your problems.
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