Calibration or Validation pt 2

In this episode, Sean and Nick wrap up the conversation around calibrating or validating analyser measurements.  Are buffer solutions safe to use by plant technicians? Is it true that calibration solutions for turbidity  sensors are carcinogenic? what is the difference between primary and secondary standards? Download and listen to find out.

Transcript

[00:00:12.730] - Sean 
This is a Yokogawa Australia New Zealand podcast. Welcome back to Yokogawa Debunks, conversations with industry experts to uncover the truth behind myths and misconceptions surrounding the industrial automation and industrial instrumentation space. I'm your host, Sean Cahill, and thank you for joining us today. In our last episode, we addressed the much-requested topic of calibrate or validate which one is better? This was done with Nick Crowe from Yokogawa and although we managed to deal with many of the misconceptions around this interesting topic, it was apparent that there were many more misconceptions which also needed clearing up. 

[00:00:51.670] - Sean 
As such, we're delighted to welcome Nick back to delve further into this subject. Welcome back, Nick. 

[00:00:57.610] - Nick 

Thanks Sean. Thanks for having me back. I'm glad to be here and we’ll continue this conversation. It's getting deeper and deeper. We'll see how far we get today. 

[00:01:06.330] - Sean 

That's great. So let's delve straight in with another common misconception that we've that we've been hearing. And this one relates to the safe use of buffers and solutions when calibrating or validating analyzers. Now there's some people that think that buffers and solutions are not that safe and and that there's a risk that could lead to health issues for technicians. Have you really come across this one in the past? 

[00:01:28.750] - Nick 

Yes, I have. Yeah, I first came across it, I think, many years ago when I worked as a service technician on process analysers, and it's understandable, really. Many analysers use chemicals or reagents and things like this, often in the internal solution that's inside a sensor or something like that. And if it's not handled correctly, does pose a risk to the person that's that's using them. So really, they should only be used by a technician who's had training, and he's going to understand the appropriate risks and hazards involved with the chemicals that he's using. 

[00:02:04.690] - Nick 
The buffers and the standards, however, for everyday use in validating and calibrating, they're not kept to the internals of the of the analyzer. So, it never seems right. When you think about using chemicals on instruments that are likely to be in contact with, you know, maybe drinking water or in food production processes, for example. And of course, analysers are also get used in environmental applications and things like that. So there's concern from some people that perhaps the calibration chemicals might get into the surrounding environment, but when I think about it carefully. 

[00:02:38.950] - Nick 

I think really, the fear comes from the raw materials that's used in the preparation of these buffers and things like that. Once they go into the buffers and they're prepared, the raw materials change their properties and they’re really diluted to very safe levels. So, they shouldn't really be any concern about it. And you know, the manufacturers of the chemicals are well aware of the kinds of applications the analysers get used in and make sure that they're safe for use. 

[00:03:05.230] - Nick 

Each one really should have its own product information sheet and have details about the correct usage and disposal instructions, too. So, you know, people do get very frightened when I think about chemicals and you know, what's this going to do to me? What long term effects are going to have on me? But yeah, there might to be as safe as possible, and it shouldn't really be too much concern there. 

[00:03:29.530] - Sean 

OK, so it does look like they come with safety data sheets or SDS, which, if read, should take away a health risk concerns. But even so, a concern that we've seen come up from time to time relates to formazin solution, which is used in turbidity calibrations. Now there's some out there who say it's carcinogenic. Would you say that there's any truth in this or is it just another one of those popular myths? 

[00:03:54.880] - Nick 

I think you use an appropriate term there, Sean. It's popular. Yeah. And I've come across this one quite a few times over the years, you know, and recently too, you know, turbidity is a subject and an obviously with an analyzer it has to be calibrated. And often, you know, they're used as final product quality check instrument. So, you have to prove the calibration, the accuracy of the instrument. So, for turbidity, calibration is quite difficult. 

[00:04:24.040] - Nick 
And the reason is that the standard solution that you're going to use is required to hold particles in suspension. And it's that bit that's really hard to achieve because particles naturally want to settle to the bottom of a liquid. So formazin was developed and it's capable of holding those particles in suspension. But there is an element in that mixture of formazin which I think is the bit that frightens most people, and that's formaldehyde. So, formaldehyde is a chemical that we want to avoid. 

[00:04:52.240] - Nick 

I don't think we hear anything but bad things about it. However, like other buffers and things like that, when it's used in formazin, it's in such low concentrations that there's really very little risk indeed. The worst risk is perhaps to the technician who's preparing the raw formazin solution ready for his calibration. And the result would likely be, you know, maybe limited to a little bit of skin irritation or maybe, you know, eye irritation if they were unfortunate enough to get a splash in their eye or something on that. 

[00:05:22.690] - Nick 

Having said that and we've said before, these chemicals should be used by trained technicians, and the same applies here with formazin and turbidity. The Procedure should really be performed by a trained tech, and he's going to be wearing appropriate PPE and ensure their own safety. When we do the calibration of turbidity, the formazin is diluted even further in this preparation and is going to be even less of a safety risk, and it should also be disposed of safely after the service. 

[00:05:51.790] - Nick 

However, this does open up another window for us here to look into, I suppose, and that's why we're on the subject of calibration versus validation. What should I be using? Should I be using a primary standard or a secondary standard? 

[00:06:07.470] - Sean 

Ok, Nick. So, what's the difference between primary standard and secondary standard? 

[00:06:12.070] - Nick 

Well, a primary standard is a solution, and it's made up of primary standard substances. It has a known purity which should be 99 percent pure, or 99.9 percent pure. It is possible to dilute this in a solvent to create your primary standard solution to a value that you desire. A secondary standard, on the other hand, is a solution which has been made by comparing it to the primary standard. 

[00:06:36.470] - Sean 

OK, well as before. Why and when should each of these be used and what's the relevance to turbidity? 

[00:06:45.400] - Nick 

Well, I raised this in the turbidity discussion because these analysers are great examples of a device that uses both types of standards throughout their life. To keep a turbidity meter up to spec requires periodic primary calibration that is done by using the formazin solution that we spoke about before. But between the primary calibrations, it's OK to use the secondary standard to validate or even calibrate the analyzer with the secondary standards. Most turbidity manufacturers will usually have a secondary standard of some kind that's included with their analyzer. 

[00:07:23.110] - Nick 

Or perhaps they have one available that you can purchase. But it is necessary to assign the secondary standard its value, and this is done by measuring it in the analyzer that's just been calibrated with the primary standard. So, they you can see there that a secondary standard is only a comparative standard to the primary standard. 

[00:07:42.040] - Sean 

So why is it then necessary to perform periodic calibrations with a primary standard? And how often should it be done? 

[00:07:49.510] - Nick 

Well, I guess the reason for the primary calibration being done periodically is simply due to the fact that the quality of the secondary calibration or standard can't be guaranteed for very long. The secondary standard is usually particularly in turbidity meters is usually a solid piece of something, so it might be a prism or a piece of glass or something like that. But throughout the time when you're using it, it's likely to get minor damages. Each time it gets bumped against the edge or wiped clean or something that you're changing its value very, very slightly. 

[00:08:22.540] - Nick 

So, we have to perform the primary calibration periodically and reassign a value to that secondary standard. 

[00:08:30.940] - Nick 

And what it does, it helps improve the long-term accuracy. So, the frequency of the primary calibration, that can change depending on the region you're working in and what the local governing body determines is necessary. 

[00:08:43.870] - Nick 

So, some regions might ask you to do a primary calibration annually. Others might ask for it to be done quarterly, and some businesses or industries will have different routines from that again. So, turbidity is most common application. It is a key indicator of water quality. And although it gets used in all sorts of other industries, the production of drinking water is most likely to be the most common. So, it's really important to ensure they are accurate because we're all going to be consuming that that produced water at the end of the day. 

[00:09:16.420] - Sean 

Previously, Nick, we spoke about how to calibrate gas analysers. Are there gas analysers that require primary and secondary standard calibrations the same as liquid analysers, for example. 

[00:09:28.120] - Nick 

Well, yes, there is a similar theory here. We've spoken before about how it's not always practical to take your gas analyzer out the process to perform a calibration, but performing the calibration can also be difficult. Unlike a liquid analyzer, you can't simply place the gas sensor into a beaker of standard. It requires some kind of calibration cell where you can be sure that the only gas present is the gas of the known standard. So, some gas analyzers are likely to be used for emissions monitoring, and others might be used for process control. 

[00:09:58.990] - Nick 

The calibration validation of each of these models have different requirements, and therefore they're going to use different methods, an Emissions Analyzer is most likely going to be required to prove its accuracy regularly. Therefore, a primary calibration is most likely to be required for that, particularly now. In a recent time that industry is likely to be paying a fine if their emissions reporting are not accurate, so they're going to want to be doing a primary calibration and prove the instrument is correct. 

[00:10:29.200] - Nick 

A Process Control Analyzer, on the other hand, is likely to be able to get away with just a validation. And then you can move to the calibration if something is found to be incorrect. As we discussed before. So yeah, it's very similar theory between primary and secondary standards and calibration and validation as well for gas analysers. 

[00:10:48.480] - Sean 

Thanks, Nick. I mean, these have been great insights and I think we've well and truly dealt with the list of misconceptions around calibration or validation that our listeners posed. To that end, I'd like to thank you once again for taking the time out of your busy schedule to talk to us today. 

[00:11:03.510] - Nick 

Thanks for having me. We look forward to chatting with you again in the future. And yeah, I hope our topic of today is of interest to some people. 

[00:11:13.260] - Sean 

And thanks to you, our listeners, for joining us once again. If you've got any questions or particular topics you'd like us to discuss, please contact us on debunks@au.yokogawa.com. Also, if you enjoyed today's episode, please remember to like, and share it on your social media channels. Now we look forward to welcoming you back for future discussions. But in the meantime, stay safe and remember, Yokogawa Debunks.