Water in the Laboratory
Virtually all labs require some form of purified water. This ranges from minimum purity applications where filtered tap water is fine to trace metal environmental analysis applications requiring type one reagent grade water, completely free of ions, microbial and organic contamination
Here are a few examples of lab applications and the implications for choosing a water purification system:
Hospital/Clinical Labs
Except for certain blood analysis protocols, where ionic purity is key, biological contamination is the main concern in the hospital environment. When we’re talking about WFI standards (water for injection), pyrogens are a concern. Though this is changing slowly around the world, distillation is still the gold standard when treating human beings. This is because, however unlikely it may be, pyrogens can bypass any filter if the filter is not intact. With distillation in stills with pyrogen traps called baffles, the water vapor goes through a series of twists and turns on the way to the condenser leaving behind all pyrogens. Pyrogens, as the name implies, cause fever.
EPA Trace Metal Labs/ Dilution of dry standards
The main requirement here is ion-free water. If you’re looking for parts per billion (PPB) of an ion, a heavy metal for instance, you have to make sure that there is ZERO presence of that ion in the water the sample is mixed with, or you get a false positive for that ionic species. As far as the dilution of often expensive standards goes, some are verified at 99.999% purity or even purer, so you want to be sure you’re not adding any of that particular ion through the water in the dilution process.
Cell Culture/ Cell Culture medium or Agar dilution.
Cell culture applications have multiplied exponentially with the advance of biotechnology and the many disciplines under the biotechnology umbrella.
While a certain level of ionic purity is required, biological purity is the big concern, and again pyrogens are an issue. Pyrogens can cause cell mutations, exactly what you DON’T want when growing a particular cell line.
But since we’re not talking about human beings in a clinical situation, these labs generally use Type 1 systems with a pyrogen filter following the 0.2 micron filter.
Methods of purification:
Deionization
Absorption
Reverse Osmosis
Filtration
Distillation
Combination Systems
Deionization
Deionization is a technique which removes ions from water and at this task it is very effective, especially in combination systems.
The macroreticular resins used in deionization are tiny particles with maximum surface area. Under a microscope, these beads have numerous bumps and spikes creating an immense amount of surface area. The surface area of a scallop is far less that that of a sea urchin of the same size.
These are high surface area resins with extremely weak ionic bonds on the surface. In Cation resin, these weak sites are initially occupied by hydrogen ions, and in the case of Anionic resins, by hydroxide, H+ and OH- respectively. Every other ion will have a greater affinity for that site on the resin than either hydrogen or hydroxide, so they stick to the resin, kicking off the weaker ions, H+ and OH-.
So as the water to be purified travels across the resin in the cartridge, it is stripped of all ions since they are stuck to the resin. And what about the H+ and OH- that were kicked off the site? Well, conveniently, H+ and OH- become HOH, also known as water. So both the ions in the water are eliminated and the rejected H+ and OH- also become pure water.
Absorption
Absorption uses activated carbon to remove chlorine and fluoride from municipal water supplies, This method is used primarily as part of combination systems. These are powerfully charged ions and you want to remove them before they get to the ion exchange sites on the macroreticular resin.
Reverse Osmosis
Reverse Osmosis is a method that removes a certain percentage of different ions. This means that ion-loaded water will still have lots of ions in it but much fewer than without RO. Approximately 95% of multivalent ions are removed and about 85% of the monovalent ions.
This technique can’t produce Type 1 water but, like activated carbon, it makes the Type 1 combination systems far more productive in terms of the number of liters produced by a set of cartidges
Filtration
Filtration physically blocks impurities from a water sample. With membrane filters, there are holes on the surface of the membrane material of a certain porosity, so larger particles are trapped on the membrane surface. Depth filters, like the air filter in a car, trap impurities throughout the body of the filter.
Examples in the lab would be a membrane filter that blocks bacteria from entering the recipient vessel. These are called sterility units that either are single use or able to withstand a sterilizer and therefore reuseable.
Depth filters in the lab are generally “pre-filters”, cotton-like polymers that trap large impurities before they physically block the tiny holes on the membrane filter.
There are dozens of sizes and membrane materials to accommodate different applications. Hydrophobicity, toxicity, and chemical resistance are just a few charaterisics of membrane filters to consider.
Disillation
The oldest and in some ways unique way to purify water is distillation. In the modern lab, stills produce VERY pure water. Not Type 1 perhaps, but as a single method to purify water without a combination system, distillation is the best, no question about that.
As mentioned before, modern stills have a baffle system which forces the water vapor on its way to the condenser to take twists and turns, leaving behind all pyrogens, and that’s why distillation is still the gold standard for water for injection in the clinical environment.
Its also good for ion elimination, just unable to produce Type 1 water since the vapor, unlike water in a Type 1 system, comes in contact with airborn carbon dioxide which does ionize, meaning that the conductivity increases. Any dissolved ion allows electrical current to flow more freely and will increase conductivity.
Conductivity ( resistivity meters actually, but it’s the same principle) meters detect this but don’t tell you which ion is easing the flow of current, and in the case of distillation, these ions are largely harmless dissolved carbon dioxide.
However, distillation has some HUGE disadvantages:
The first is energy consumption. Boiling water takes far more energy than any other purification method.
Perhaps more problematic is the nature of the method itself. With all the other separation techniques, we are removing impurities from the water…but distillation removes the water from the impurities.
This means all the impurities stay behind in the boiler chamber. This reduces efficiency over time as the impurities encrust themselves on the inner boiler surface, and cleaning the surface can imply the use of hazardous materials with the attendant OSHA issues.
Combination systems:
Type 1 water is so ionically pure that if you drink it, it will burn you as the ultrapure water, a powerful solvent, sucks the electrolytes from your tongue.
All Type 1 systems purify through ionic exchange resin treatment, then filter for biological impurities, including pyrogens The key to the lab manager’s budget efficiency is to make the ion exchange sites last as long as possible. So we pretreat the feedwater with reverse osmosis and activated carbon to get the water ready for “polishing”
Ultrapure water is a liquid uncomfortable with itself, it wants ions. That’s why Type 1 water systems constantly push the water through the system, so that its always passing by the macroreticular resin. This recirculation continues until the scientist pushes the button, releasing verifiably pure Type 1 reagent grade water
Virtually all labs require some form of purified water. This ranges from minimum purity applications where filtered tap water is fine to trace metal environmental analysis applications requiring type one reagent grade water, completely free of ions, microbial and organic contamination
Here are a few examples of lab applications and the implications for choosing a water purification system:
Hospital/Clinical Labs
Except for certain blood analysis protocols, where ionic purity is key, biological contamination is the main concern in the hospital environment. When we’re talking about WFI standards (water for injection), pyrogens are a concern. Though this is changing slowly around the world, distillation is still the gold standard when treating human beings. This is because, however unlikely it may be, pyrogens can bypass any filter if the filter is not intact. With distillation in stills with pyrogen traps called baffles, the water vapor goes through a series of twists and turns on the way to the condenser leaving behind all pyrogens. Pyrogens, as the name implies, cause fever.
EPA Trace Metal Labs/ Dilution of dry standards
The main requirement here is ion-free water. If you’re looking for parts per billion (PPB) of an ion, a heavy metal for instance, you have to make sure that there is ZERO presence of that ion in the water the sample is mixed with, or you get a false positive for that ionic species. As far as the dilution of often expensive standards goes, some are verified at 99.999% purity or even purer, so you want to be sure you’re not adding any of that particular ion through the water in the dilution process.
Cell Culture/ Cell Culture medium or Agar dilution.
Cell culture applications have multiplied exponentially with the advance of biotechnology and the many disciplines under the biotechnology umbrella.
While a certain level of ionic purity is required, biological purity is the big concern, and again pyrogens are an issue. Pyrogens can cause cell mutations, exactly what you DON’T want when growing a particular cell line.
But since we’re not talking about human beings in a clinical situation, these labs generally use Type 1 systems with a pyrogen filter following the 0.2 micron filter.
Methods of purification:
Deionization
Absorption
Reverse Osmosis
Filtration
Distillation
Combination Systems
Deionization
Deionization is a technique which removes ions from water and at this task it is very effective, especially in combination systems.
The macroreticular resins used in deionization are tiny particles with maximum surface area. Under a microscope, these beads have numerous bumps and spikes creating an immense amount of surface area. The surface area of a scallop is far less that that of a sea urchin of the same size.
These are high surface area resins with extremely weak ionic bonds on the surface. In Cation resin, these weak sites are initially occupied by hydrogen ions, and in the case of Anionic resins, by hydroxide, H+ and OH- respectively. Every other ion will have a greater affinity for that site on the resin than either hydrogen or hydroxide, so they stick to the resin, kicking off the weaker ions, H+ and OH-.
So as the water to be purified travels across the resin in the cartridge, it is stripped of all ions since they are stuck to the resin. And what about the H+ and OH- that were kicked off the site? Well, conveniently, H+ and OH- become HOH, also known as water. So both the ions in the water are eliminated and the rejected H+ and OH- also become pure water.
Absorption
Absorption uses activated carbon to remove chlorine and fluoride from municipal water supplies, This method is used primarily as part of combination systems. These are powerfully charged ions and you want to remove them before they get to the ion exchange sites on the macroreticular resin.
Reverse Osmosis
Reverse Osmosis is a method that removes a certain percentage of different ions. This means that ion-loaded water will still have lots of ions in it but much fewer than without RO. Approximately 95% of multivalent ions are removed and about 85% of the monovalent ions.
This technique can’t produce Type 1 water but, like activated carbon, it makes the Type 1 combination systems far more productive in terms of the number of liters produced by a set of cartidges
Filtration
Filtration physically blocks impurities from a water sample. With membrane filters, there are holes on the surface of the membrane material of a certain porosity, so larger particles are trapped on the membrane surface. Depth filters, like the air filter in a car, trap impurities throughout the body of the filter.
Examples in the lab would be a membrane filter that blocks bacteria from entering the recipient vessel. These are called sterility units that either are single use or able to withstand a sterilizer and therefore reuseable.
Depth filters in the lab are generally “pre-filters”, cotton-like polymers that trap large impurities before they physically block the tiny holes on the membrane filter.
There are dozens of sizes and membrane materials to accommodate different applications. Hydrophobicity, toxicity, and chemical resistance are just a few charaterisics of membrane filters to consider.
Disillation
The oldest and in some ways unique way to purify water is distillation. In the modern lab, stills produce VERY pure water. Not Type 1 perhaps, but as a single method to purify water without a combination system, distillation is the best, no question about that.
As mentioned before, modern stills have a baffle system which forces the water vapor on its way to the condenser to take twists and turns, leaving behind all pyrogens, and that’s why distillation is still the gold standard for water for injection in the clinical environment.
Its also good for ion elimination, just unable to produce Type 1 water since the vapor, unlike water in a Type 1 system, comes in contact with airborn carbon dioxide which does ionize, meaning that the conductivity increases. Any dissolved ion allows electrical current to flow more freely and will increase conductivity.
Conductivity ( resistivity meters actually, but it’s the same principle) meters detect this but don’t tell you which ion is easing the flow of current, and in the case of distillation, these ions are largely harmless dissolved carbon dioxide.
However, distillation has some HUGE disadvantages:
The first is energy consumption. Boiling water takes far more energy than any other purification method.
Perhaps more problematic is the nature of the method itself. With all the other separation techniques, we are removing impurities from the water…but distillation removes the water from the impurities.
This means all the impurities stay behind in the boiler chamber. This reduces efficiency over time as the impurities encrust themselves on the inner boiler surface, and cleaning the surface can imply the use of hazardous materials with the attendant OSHA issues.
Combination systems:
Type 1 water is so ionically pure that if you drink it, it will burn you as the ultrapure water, a powerful solvent, sucks the electrolytes from your tongue.
All Type 1 systems purify through ionic exchange resin treatment, then filter for biological impurities, including pyrogens The key to the lab manager’s budget efficiency is to make the ion exchange sites last as long as possible. So we pretreat the feedwater with reverse osmosis and activated carbon to get the water ready for “polishing”
Ultrapure water is a liquid uncomfortable with itself, it wants ions. That’s why Type 1 water systems constantly push the water through the system, so that its always passing by the macroreticular resin. This recirculation continues until the scientist pushes the button, releasing verifiably pure Type 1 reagent grade water.