Dr. Estelle Riche: Hello. Welcome to this webinar on best practices for using a water purification system. My name is Estelle Riche, and I'm Senior Scientist in the training and application group of the lab water business field of Merck Millipore
You may have a water purification system in your lab, and you may be wondering about the best way to use it. So, in the next few minutes, I will give you some tips about the best way to handle both your water purification system and the high quality water that it delivers
So, the reason why we are talking about water today is because water is used in many different places in the laboratory. It is a very common reagent, and it is also probably the most abundant reagent you may use in your lab
It may be used to prepare reagents and standards, to prepare buffers and mobile phases for chromatography. It is often used as blank [sp] or in sample preparations for dilution, rinsing or extraction
It may also be used for washing and rinsing containers. And this is something to always remember. Please take care of your containers and glassware by using high purity water for the last rinse. It will prevent any risk of contamination of your glassware. We will talk about this further on in the presentation
So, what's really important for the water you use in your laboratory is that it needs to be free of any contamination that may compromise your results. And in the remainder of the presentation, I will explain to you how you can do this and get the best results
Okay. So, first of all, we may think about what is in water, what other molecules are in water aside from HTO. So, if you turn on your tap water, what comes out of it is of course mostly HTO molecules, but as well, other contaminants
The contaminants are usually grouped into five main families. First of all, you may have some ions in your water that come from the [unintelligible] it was in contact with. There may be some minerals like calcium, magnesium, also some chlorine, for example, and many other items
Your water may also contain some organic molecules that come from nature. As leaves as pieces degrade into water, they release some organic molecules
There may also be some very small amounts of other contaminants that come from human activity such as pesticides or maybe plasticizers or even medications might be present now in tap water in very, very small amounts. So, it is not bad for your health. However, it may have an impact on your experiments in the lab
Other contaminants that may be present in water are particles that come from maybe grains of sand or just, you know, very, very small pieces of objects that were in contact with natural water. There may also be some bacteria in your tap water. So, of course, there are no harmful bacteria because those are treated with chlorine and other compounds like this. However, there may be some harmless bacteria since bacteria are everywhere in our environment, anyway
And, finally, there may be a few dissolved gasses in your water
All right. So, this is the reason why water needs to be purified before you use it in your laboratory because it may contain some contaminants that will have an impact on your experiments
So, usually, water purification is performed in two steps. The first step is called the pre-treatment, and it goes from tap water to what we usually call pure water. And then, the second step is called the polishing step, and this is what will give you really, really high quality water, which is also called ultra pure water
Water purification is usually done by combining different technologies in order to be sure to move all the different types of contaminants that are present in water
Usually, in the first step, in the pre-treatment step, what is used is reverse osmosis. Reverse osmosis is a technology based on a porous membrane through which we apply pressure. So, only water molecules will go through, and other molecules will be retained on the other side of the membrane
So, this technology is really efficient at removing a wide variety of contaminants. As you can see below, it can remove ions, organics, particles and bacteria. However, it will not remove 100 percent of them, but depending on the type of contaminant, it may remove between 95 to even 99 percent of those contaminants
So, this is really efficient. It's a very good first step. However, this technology is very sensitive to particularly [unintelligible] chlorine. This is the reason why we have a pretreatment cartridge to protect it
Then, the next technology that is very often used in a purification system is called electrode deionization. So, this technology is just a more advanced technology than simple ion exchange, but it serves the same purpose. So, it removes ions
It is very efficient at removing ions, but it will not do anything else than that
The following technology, you can see, is UV light. So, UV at 254 nanometers is used in order to keep bacteria under control. This will actually have an effect on the DNA of bacteria and kill them or at least suppress them
So, now I've described the technologies for the pretreatment. Now, if you need water that is of really, really high quality in order to perform experiments such as HPLC, ICPMS, this type of very, very sensitive analysis, then you will use a polishing system - like, for example, the Milli-Q system
This system will combine, once again, some UV lights. But, this is UV at a different wave length, which will actually photo oxidize organic molecules and break them down into small pieces
It also uses a combination of ion exchange resin, which will remove ions as its name suggests, as well as activated carbon, which is really efficient at removing organic molecules
So, overall, the combination of all those technologies will give you water that is of extremely high quality. Then, the last step is usually a filter, a .22 micron filter, in order to remove whatever is left of bacteria and particles
So, now that I've explained to you what types of contaminants are removed from your water in order to generate water for your lab, I will talk to you a little bit about how you can optimize the quality of water that comes out of your water purification system, because using a system is a very good first step, but it is not the only step that you should take into account
So, the first advice I would have for you is to really perform regular preventative maintenance. This is the same as you would do for your car. It's always better to do regular maintenance instead of waiting for it to break down. This is the same for your water purification system
So, please be sure to replace your cartridges and your filters on a regular basis as it explains in your manual. And also, when new cartridges are installed, please be sure to rinse them a little bit at the beginning just to be sure that gives you the optimal level of water purity
So, just as an example of the impact of not changing filters on time--for example, this is about the final filter, the .2 micron filter that is usually placed at the very end of a water purification system. What is shown here is a UPLC chromatogram
So, the red line is what happens when older filter is kept on the system. And as you can see here, there is a non-peak that appears at about three minutes on the UPLC
However, if the same user changes his final filter and uses a new one, then the baseline becomes of much higher quality. So, really, it's important to be sure to change filters and packs on time
Another advice I would like to give you is to monitor the quality of the water you obtain from your water purification system. So, most systems will display some values, like this one. And I will explain to you quickly what these numbers really mean
So, first of all, one important contaminant to monitor are ions. And the way we monitor ions in water is by simply looking at electrical conductivity because extremely pure water without any ions in it will really not conduct electricity very well. And the more ions are present in water, the more it will conduct electricity
So, really, conductivity is a very easy and meaningful way of looking at ion contamination of water
So, if water is extremely pure, the theoretical value of conductivity of that water will be 0.055 microsiemens per centimeter at 25 degrees Celsius. And since its value is not so easy maybe to talk about, usually, people report the resistivity
Resistivity is the reciprocal of conductivity. And in this case, if you have extremely high quality water, its resistivity will be 18.2 mega ohm centimeter at 25 degrees Celsius
And I'm sure if you have a good quality water purification system in your laboratory, you have seen this magic number of 18.2 being displayed on the instrument. This reflects the purity as far as ions are concerned
So, as we have described earlier, ions are not the only important contaminants in water. Other contaminants to worry about are organics because organics may have an impact on your experiment
So, it is very important to also monitor the level of organics in your water. And this is done by measuring what is called the TOC, which is the Total Oxidizable Carbon
This really represents the total amount of ranic [sp] substances that are in the water. And it is usually expressed in parts per billion, which means micrograms per liter. And it is measured by simply oxidizing and then detecting the result of the oxidation
Those two values, the TOC value and the resistivity value, are both extremely important to reflect the quality of the water you will be using for your experiments
It is important, however, to remember that resistivity and TOC values have no correlation. So, just because your system displays a resistivity of 18.2 mega ohm centimeter does not mean that your water is extremely pure. It may contain a lot of organics that you may not even see that organics are present because resistivity only looks at ions
So, this is just the small experiments we did to express this. What we did is we added some sugar to the reservoir, and then that water was passed through a polishing system. So, after a while, the polishing system was overwhelmed by the huge amount of sugar present in the water
And so, what you can see here is that, in blue, the resistivity remains the same. There are very few ions, and that water is really good
However, the TOC goes up drastically over 1,000 PPB [sp]. This is really to show you that 18.2 mega ohm centimeter is only part of the indication you need to know whether your water is good or not
Another good practice with water purification systems is to flush the system before collecting water. This is really true if the system has been idling. For example, when you arrive on Monday morning, if the system has not been used in the weekend, I would recommend you to discard a little bit of water before you start collecting water for your experiments
So, these two graphs are just to show you what happens on HPLC, for example if you take water right away. So, the pink lines are after just 100 milliliters of water being disposed of
And then, as you can see, when one liter has been discarded in yellow, then it's a little bit better. But then, when five liters have been discarded - that's the green line - you can see that both in HPLC or in LCMS, the baselines are of much higher quality
So, don't hesitate to discard a few liters of water. This is done very quickly. It takes just a minute or two. And this will really greatly improve your results
Another case where it's important to flush water from your system before collecting water is if you're worried about bacteria contamination. So, most systems have a filter at the end at the point of use. This filter is a .22 micron filter that is designed to retain particulates and bacteria
However, as you can see here, if water is collected right away, there are a few bacteria present. You know, depending on the day, it may vary between five a 86 CFUs [sp] per ML
And if, however, you discard a little bit of water, then you will not see any bacteria coming out of the system and of the filter. So, what this indicates is that the bacteria actually came from the ambient air and penetrated into the outside part of the membrane
So, it's really important to flush out those bacteria that come from the air in order to have really clean water without bacteria
So, once again, a few liters, so that will take a minute or two. And that's perfect. You will have high quality water
Another good practice is really to use freshly purified water and try not to store highly pure water, because unfortunately, high purity water is an excellent solvent, and it will not stay highly pure for a very long time. Since it is extremely pure, it will tend to try to grab contamination from its environment
So, whether it is from the air of the lab or from the container it is placed in, it will tend to degrade. So, if at all possible, try to use really, really freshly purified water
So, to illustrate the potential for the air of the lab to contaminate your ultra pure water, you may notice that your water is contaminated with ammonia, which is very present in laboratory air, and another thing that will happen is that C02 will contaminate high purity water by dissolving into it and generate bicarbonate and carbonate, which will increase the conductivity of the water or decrease its resistivity
The air of your laboratory does not only contain ions that may contaminate ultra pure water, but it probably also contains organics that may contaminate water, as well. Those may come from organic solvents that are used in the lab
So, this experiment is to show this. So, this is electronic spray ionization Maspeck [sp]. And what you can see here is that the freshly purified water on the left has a very low level of organic contamination. However, after two months of keeping water in the bottle and just opening it in the air about three times per week for 15 minutes, then the level of organic contamination is much, much higher
So, usually, the recommendation I would have if you do organic analysis, HPLC, UHPLC or LCMS, I would recommend you use freshly purified water every day. So, every morning, discard whatever is left of the water from the day before and get freshly purified water. That way, you can really be sure your results will be the best
So, just to show you the effect that storage may have on HPLC, not only does water get contaminated from the air of the lab, but it can also contaminated from the container it is placed in. Once thing that is really not very good when you do organic analysis is to use plastic to store ultra pure water
What you can see here is these are baselines obtained from water that was stored in plastic for a few days. And really, even just on the first day, it's not good to have water in plastic. What happens is plasticizers are released from the container into the ultra pure water, and then you will see those on your chromatogram
So, really, it is important to avoid plastic at all cost if you do organic analysis
Now, if you do ion analysis, then issues can happen, as well. In addition to having contamination from the air, potentially, you may also have, of course, contamination from the container if it contains some ions
Another thing to worry about is try not to keep standards for too long. So, this was just a small experiment that was done by--where standards were prepared in the evening and ran right away and then kept overnight in an auto sampler and ran again
And what you can see here is that the levels of both the sodium and the magnesium have increased overnight. So, we don't know exactly where that contamination comes from. Is it from the head space in the vile or is it from the vile itself? We're not sure
But, in any case, it truly shows you that standards [sp] need to be prepared fresh in order to get the best results
Another good practice is to really be sure to select the proper container for your analysis. So, it is quite common knowledge that it is better to use plastic containers if you do ion or [unintelligible] analysis, and it is also better to use glass containers if you do organic analysis
In all cases, your containers should be really carefully washed and rinsed. In our research laboratories here at Merck Millipore, we really try in many cases not even to use any detergent in the containers that we use and use, for example, for elemental [sp] analysis, we use acid, and then rinse a lot with high purity water
It is also not good to mix containers from one type of analysis to another because there is more of a risk for contamination. So, all those are really common sense pieces of advice, but these are really quite important, especially if you perform trace analysis
So, just as an illustration to show you that containers may actually contaminate your samples with organics, for example, here is a case where we used either polyethylene HDPE containers or PP [sp] containers, and we simply placed some really high quality Milli-Q water inside those containers and rinsed them for 24 hours, and then discarded, and then added more water for another 24 hours, discarded again and repeated this three times
What you can see here is that the level of TOC, so the level of organics present in that water is quite high on the first time. And then, as time goes on, then it goes down. So, that means that the level of extractables is very high at the beginning, and as time goes by, as the volume of Milli-Q water in contact with those containers increases, then the amount of extractables goes down
So, this is one of the cases where it may be better actually to use older containers than to use new ones because the older ones will have been very well rinsed and will no longer have extractables that may go into your sample
For those of you who work with ions or elemental analysis, the issue is quite similar. And even if you use really high quality containers, it's really important to rinse them really well. And depending on the level of your analysis, if--you may still see some contamination. No matter what you do, you may still see low levels of contamination
This is, for example, beta from ICPMS experiments where you can see that both PSA and PBC will release some elements, even though PSA seems better for some contaminants or PBC better for others. So, depending on the type of ions you analyze, you need to really select the proper container for your experiments
So, another piece of advice I would have for the use for your water purification system is to really try to avoid using plastic tubing at the outlet of your system because this plastic tubing will really bring some contamination into your water. So, basically, what happens here is that the water delivered by the purification system is of really high quality, and then when it gets in contact with the plastic, it will either get some plasticizers from the plastic or even bacteria or algae may develop in the plastic tubing
So, at the end, the water you will collect after these pieces of tubing will be of much lower quality. So, this is really a very simple but very important piece of advice
Another quite simple and straightforward piece of advice is to try not to collate [sp] water straight down into a container because this will generate bubbles. And those bubbles may bring in contamination into your sample. They will bring air from the lab, and this air, as we've discussed earlier, may contain some ions that will contaminate your sample
So, I would recommend to you, tilt a little bit the bottle or the container you use to collect water, whether it is to prepare to your samples or to prepare LUNs [sp], for example, for chromatography, in order to avoid forming any bubbles in your container
Another good practice is to try to minimize the use of wash bottles. I know wash bottles are extremely convenient in the laboratory, but the problem is even if water is of really high quality at the time when you put it in the bottle after a little while, you can be sure that the quality of the water will degrade quite a bit. And then, you will not know what you're using to rinse with your wash bottle, and you may actually really introduce some contamination by using those bottles
You know, the plastic of the bottle itself may contaminate the water, but also the air of the lab may contaminate it. So, if there are some volatile organics in your lab, they will penetrate in the wash bottle. C02, of course, will penetrate. Other ions will penetrate
So, it's always best to use water that comes directly from the system instead of going through a wash bottle, as much as you can, of course
All right. And as I'm getting towards the end of my presentation, I wanted just to give you a few additional tips really quickly
So, one thing it's important to keep your water purification system as well as the container you may use to store water, even though we said it's better not to store it, in a clean environment. If you're storing water in, for example, a wash room that's quite dirty or near a hood that's being used with strong organics or that is quite dirty, then you may contaminate your high purity water
So, it's really important to look around and be sure to place it in the best location in your laboratory
Another small tip is, once you collect water from a system, try not to walk around in the lab with your open container because it will increase the risk of contamination from the lab air. So, if you can, then collect water in a bottle in something you can close before you walk in the lab with it
Another thing is that not only solvents in the laboratory can contaminate water, other things can contaminate it such as cleaning products or glue or paint or furniture from your lab. If you're doing extremely sensitive trace analysis, make sure you watch out for those, really. Once again, think about your environment because ultra pure water is extremely, extremely sensitive to all those contaminants that might be present in the air
Finally, another thing to watch out for is the use of all base pans, scotch tape or label tape, perfume. All these types of products may release some contamination into the air and into your water, as well
And finally, the source of contamination of your water may actually not come from water. It may actually come from something else
This is just an example of a case where the contamination actually did not come from the water but came from the small amount of reagent that was added to water in order to prepare mobile space [sp] for ion chromatography
So, really, here my advice is to--of course, you know this--but to use really the highest purity reagent possible
And finally, one last piece of advice is to watch out for the filters you use to prepare your sample. You may have a really high quality sample, but if you don't use the proper type of filter, you may actually introduce quite a bit of contamination into your sample
So, here you can see just an HPLC trace, and you can see additional peaks that appear, and that came from using the wrong type of filter. But, filters may also release ions in addition to organics. So, this is really something to watch out for
So, in conclusion, I hope I convinced you that water is not just water. Even though water used everywhere in the laboratory and may feel like this is a very common solvent. It is really a reagent, and it should really be used in the same way as you would use other reagents. And you should take the same care with your water as you would take with other reagents in your laboratory
Another thing I hope you understood from my presentation today is that really having a good quality water purification system in your laboratory is a wonderful thing. However, it's only the first step
Once you have a good system, then you need to be sure you really use it in the correct way and that you maintain it properly so that you continue having the best water quality possible available for all your experiments
And finally, I gave you today some good laboratory practice ideas in order to obtain really high purity water, and this will really be important for you to get the best results for your experiments and really boost your laboratory productivity
This is the end of my presentation. Thank you very much for your attention
Below, you will find my email address. Don't hesitate to contact me if you have any question about this presentation
You may also visit our website at www.merckmillipore.com if you want more information about our water purification systems, the various technologies and the various applications for them. Thank you very much